This README is intended to help maintainers move their SPI drivers over to driver model. It works through the required steps with an example. Signed-off-by: Simon Glass <sjg@chromium.org> Reviewed-by: Jagannadha Sutradharudu Teki <jagannadh.teki@gmail.com>master
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How to port a SPI driver to driver model |
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======================================== |
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|
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Here is a rough step-by-step guide. It is based around converting the |
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exynos SPI driver to driver model (DM) and the example code is based |
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around U-Boot v2014.10-rc2 (commit be9f643). |
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|
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It is quite long since it includes actual code examples. |
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|
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Before driver model, SPI drivers have their own private structure which |
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contains 'struct spi_slave'. With driver model, 'struct spi_slave' still |
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exists, but now it is 'per-child data' for the SPI bus. Each child of the |
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SPI bus is a SPI slave. The information that was stored in the |
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driver-specific slave structure can now be port in private data for the |
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SPI bus. |
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|
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For example, struct tegra_spi_slave looks like this: |
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struct tegra_spi_slave { |
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struct spi_slave slave; |
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struct tegra_spi_ctrl *ctrl; |
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}; |
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|
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In this case 'slave' will be in per-child data, and 'ctrl' will be in the |
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SPI's buses private data. |
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|
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0. How long does this take? |
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You should be able to complete this within 2 hours, including testing but |
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excluding preparing the patches. The API is basically the same as before |
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with only minor changes: |
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- methods to set speed and mode are separated out |
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- cs_info is used to get information on a chip select |
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1. Enable driver mode for SPI and SPI flash |
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Add these to your board config: |
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#define CONFIG_DM_SPI |
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#define CONFIG_DM_SPI_FLASH |
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2. Add the skeleton |
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Put this code at the bottom of your existing driver file: |
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struct spi_slave *spi_setup_slave(unsigned int busnum, unsigned int cs, |
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unsigned int max_hz, unsigned int mode) |
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{ |
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return NULL; |
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} |
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|
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struct spi_slave *spi_setup_slave_fdt(const void *blob, int slave_node, |
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int spi_node) |
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{ |
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return NULL; |
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} |
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|
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static int exynos_spi_ofdata_to_platdata(struct udevice *dev) |
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{ |
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return -ENODEV; |
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} |
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static int exynos_spi_probe(struct udevice *dev) |
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{ |
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return -ENODEV; |
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} |
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static int exynos_spi_remove(struct udevice *dev) |
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{ |
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return -ENODEV; |
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} |
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static int exynos_spi_claim_bus(struct udevice *dev) |
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{ |
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return -ENODEV; |
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} |
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static int exynos_spi_release_bus(struct udevice *dev) |
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{ |
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return -ENODEV; |
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} |
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static int exynos_spi_xfer(struct udevice *dev, unsigned int bitlen, |
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const void *dout, void *din, unsigned long flags) |
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{ |
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return -ENODEV; |
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} |
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static int exynos_spi_set_speed(struct udevice *dev, uint speed) |
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{ |
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return -ENODEV; |
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} |
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static int exynos_spi_set_mode(struct udevice *dev, uint mode) |
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{ |
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return -ENODEV; |
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} |
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static int exynos_cs_info(struct udevice *bus, uint cs, |
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struct spi_cs_info *info) |
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{ |
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return -ENODEV; |
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} |
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static const struct dm_spi_ops exynos_spi_ops = { |
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.claim_bus = exynos_spi_claim_bus, |
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.release_bus = exynos_spi_release_bus, |
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.xfer = exynos_spi_xfer, |
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.set_speed = exynos_spi_set_speed, |
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.set_mode = exynos_spi_set_mode, |
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.cs_info = exynos_cs_info, |
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}; |
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static const struct udevice_id exynos_spi_ids[] = { |
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{ .compatible = "samsung,exynos-spi" }, |
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{ } |
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}; |
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U_BOOT_DRIVER(exynos_spi) = { |
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.name = "exynos_spi", |
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.id = UCLASS_SPI, |
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.of_match = exynos_spi_ids, |
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.ops = &exynos_spi_ops, |
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.ofdata_to_platdata = exynos_spi_ofdata_to_platdata, |
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.probe = exynos_spi_probe, |
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.remove = exynos_spi_remove, |
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}; |
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|
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3. Replace 'exynos' in the above code with your driver name |
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4. #ifdef out all of the code in your driver except for the above |
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This will allow you to get it building, which means you can work |
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incrementally. Since all the methods return an error initially, there is |
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less chance that you will accidentally leave something in. |
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|
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Also, even though your conversion is basically a rewrite, it might help |
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reviewers if you leave functions in the same place in the file, |
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particularly for large drivers. |
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5. Add some includes |
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Add these includes to your driver: |
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#include <dm.h> |
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#include <errno.h> |
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6. Build |
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At this point you should be able to build U-Boot for your board with the |
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empty SPI driver. You still have empty methods in your driver, but we will |
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write these one by one. |
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|
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If you have spi_init() functions or the like that are called from your |
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board then the build will fail. Remove these calls and make a note of the |
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init that needs to be done. |
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7. Set up your platform data structure |
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This will hold the information your driver to operate, like its hardware |
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address or maximum frequency. |
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You may already have a struct like this, or you may need to create one |
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from some of the #defines or global variables in the driver. |
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Note that this information is not the run-time information. It should not |
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include state that changes. It should be fixed throughout the live of |
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U-Boot. Run-time information comes later. |
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Here is what was in the exynos spi driver: |
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struct spi_bus { |
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enum periph_id periph_id; |
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s32 frequency; /* Default clock frequency, -1 for none */ |
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struct exynos_spi *regs; |
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int inited; /* 1 if this bus is ready for use */ |
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int node; |
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uint deactivate_delay_us; /* Delay to wait after deactivate */ |
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}; |
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Of these, inited is handled by DM and node is the device tree node, which |
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DM tells you. The name is not quite right. So in this case we would use: |
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struct exynos_spi_platdata { |
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enum periph_id periph_id; |
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s32 frequency; /* Default clock frequency, -1 for none */ |
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struct exynos_spi *regs; |
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uint deactivate_delay_us; /* Delay to wait after deactivate */ |
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}; |
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8a. Write ofdata_to_platdata() [for device tree only] |
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This method will convert information in the device tree node into a C |
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structure in your driver (called platform data). If you are not using |
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device tree, go to 8b. |
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DM will automatically allocate the struct for us when we are using device |
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tree, but we need to tell it the size: |
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U_BOOT_DRIVER(spi_exynos) = { |
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... |
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.platdata_auto_alloc_size = sizeof(struct exynos_spi_platdata), |
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Here is a sample function. It gets a pointer to the platform data and |
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fills in the fields from device tree. |
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static int exynos_spi_ofdata_to_platdata(struct udevice *bus) |
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{ |
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struct exynos_spi_platdata *plat = bus->platdata; |
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const void *blob = gd->fdt_blob; |
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int node = bus->of_offset; |
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plat->regs = (struct exynos_spi *)fdtdec_get_addr(blob, node, "reg"); |
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plat->periph_id = pinmux_decode_periph_id(blob, node); |
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if (plat->periph_id == PERIPH_ID_NONE) { |
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debug("%s: Invalid peripheral ID %d\n", __func__, |
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plat->periph_id); |
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return -FDT_ERR_NOTFOUND; |
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} |
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/* Use 500KHz as a suitable default */ |
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plat->frequency = fdtdec_get_int(blob, node, "spi-max-frequency", |
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500000); |
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plat->deactivate_delay_us = fdtdec_get_int(blob, node, |
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"spi-deactivate-delay", 0); |
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debug("%s: regs=%p, periph_id=%d, max-frequency=%d, deactivate_delay=%d\n", |
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__func__, plat->regs, plat->periph_id, plat->frequency, |
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plat->deactivate_delay_us); |
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return 0; |
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} |
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8b. Add the platform data [non-device-tree only] |
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Specify this data in a U_BOOT_DEVICE() declaration in your board file: |
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struct exynos_spi_platdata platdata_spi0 = { |
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.periph_id = ... |
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.frequency = ... |
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.regs = ... |
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.deactivate_delay_us = ... |
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}; |
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U_BOOT_DEVICE(board_spi0) = { |
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.name = "exynos_spi", |
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.platdata = &platdata_spi0, |
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}; |
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You will unfortunately need to put the struct into a header file in this |
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case so that your board file can use it. |
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9. Add the device private data |
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Most devices have some private data which they use to keep track of things |
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while active. This is the run-time information and needs to be stored in |
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a structure. There is probably a structure in the driver that includes a |
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'struct spi_slave', so you can use that. |
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struct exynos_spi_slave { |
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struct spi_slave slave; |
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struct exynos_spi *regs; |
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unsigned int freq; /* Default frequency */ |
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unsigned int mode; |
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enum periph_id periph_id; /* Peripheral ID for this device */ |
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unsigned int fifo_size; |
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int skip_preamble; |
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struct spi_bus *bus; /* Pointer to our SPI bus info */ |
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ulong last_transaction_us; /* Time of last transaction end */ |
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}; |
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We should rename this to make its purpose more obvious, and get rid of |
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the slave structure, so we have: |
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struct exynos_spi_priv { |
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struct exynos_spi *regs; |
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unsigned int freq; /* Default frequency */ |
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unsigned int mode; |
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enum periph_id periph_id; /* Peripheral ID for this device */ |
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unsigned int fifo_size; |
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int skip_preamble; |
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ulong last_transaction_us; /* Time of last transaction end */ |
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}; |
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DM can auto-allocate this also: |
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U_BOOT_DRIVER(spi_exynos) = { |
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... |
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.priv_auto_alloc_size = sizeof(struct exynos_spi_priv), |
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Note that this is created before the probe method is called, and destroyed |
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after the remove method is called. It will be zeroed when the probe |
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method is called. |
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10. Add the probe() and remove() methods |
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Note: It's a good idea to build repeatedly as you are working, to avoid a |
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huge amount of work getting things compiling at the end. |
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The probe method is supposed to set up the hardware. U-Boot used to use |
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spi_setup_slave() to do this. So take a look at this function and see |
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what you can copy out to set things up. |
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static int exynos_spi_probe(struct udevice *bus) |
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{ |
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struct exynos_spi_platdata *plat = dev_get_platdata(bus); |
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struct exynos_spi_priv *priv = dev_get_priv(bus); |
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priv->regs = plat->regs; |
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if (plat->periph_id == PERIPH_ID_SPI1 || |
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plat->periph_id == PERIPH_ID_SPI2) |
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priv->fifo_size = 64; |
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else |
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priv->fifo_size = 256; |
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priv->skip_preamble = 0; |
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priv->last_transaction_us = timer_get_us(); |
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priv->freq = plat->frequency; |
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priv->periph_id = plat->periph_id; |
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return 0; |
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} |
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This implementation doesn't actually touch the hardware, which is somewhat |
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unusual for a driver. In this case we will do that when the device is |
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claimed by something that wants to use the SPI bus. |
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For remove we could shut down the clocks, but in this case there is |
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nothing to do. DM frees any memory that it allocated, so we can just |
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remove exynos_spi_remove() and its reference in U_BOOT_DRIVER. |
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11. Implement set_speed() |
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This should set up clocks so that the SPI bus is running at the right |
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speed. With the old API spi_claim_bus() would normally do this and several |
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of the following functions, so let's look at that function: |
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int spi_claim_bus(struct spi_slave *slave) |
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{ |
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struct exynos_spi_slave *spi_slave = to_exynos_spi(slave); |
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struct exynos_spi *regs = spi_slave->regs; |
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u32 reg = 0; |
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int ret; |
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ret = set_spi_clk(spi_slave->periph_id, |
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spi_slave->freq); |
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if (ret < 0) { |
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debug("%s: Failed to setup spi clock\n", __func__); |
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return ret; |
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} |
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exynos_pinmux_config(spi_slave->periph_id, PINMUX_FLAG_NONE); |
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spi_flush_fifo(slave); |
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reg = readl(®s->ch_cfg); |
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reg &= ~(SPI_CH_CPHA_B | SPI_CH_CPOL_L); |
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if (spi_slave->mode & SPI_CPHA) |
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reg |= SPI_CH_CPHA_B; |
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if (spi_slave->mode & SPI_CPOL) |
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reg |= SPI_CH_CPOL_L; |
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writel(reg, ®s->ch_cfg); |
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writel(SPI_FB_DELAY_180, ®s->fb_clk); |
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return 0; |
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} |
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It sets up the speed, mode, pinmux, feedback delay and clears the FIFOs. |
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With DM these will happen in separate methods. |
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Here is an example for the speed part: |
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static int exynos_spi_set_speed(struct udevice *bus, uint speed) |
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{ |
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struct exynos_spi_platdata *plat = bus->platdata; |
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struct exynos_spi_priv *priv = dev_get_priv(bus); |
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int ret; |
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if (speed > plat->frequency) |
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speed = plat->frequency; |
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ret = set_spi_clk(priv->periph_id, speed); |
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if (ret) |
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return ret; |
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priv->freq = speed; |
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debug("%s: regs=%p, speed=%d\n", __func__, priv->regs, priv->freq); |
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return 0; |
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} |
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12. Implement set_mode() |
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This should adjust the SPI mode (polarity, etc.). Again this code probably |
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comes from the old spi_claim_bus(). Here is an example: |
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static int exynos_spi_set_mode(struct udevice *bus, uint mode) |
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{ |
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struct exynos_spi_priv *priv = dev_get_priv(bus); |
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uint32_t reg; |
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reg = readl(&priv->regs->ch_cfg); |
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reg &= ~(SPI_CH_CPHA_B | SPI_CH_CPOL_L); |
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if (mode & SPI_CPHA) |
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reg |= SPI_CH_CPHA_B; |
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if (mode & SPI_CPOL) |
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reg |= SPI_CH_CPOL_L; |
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writel(reg, &priv->regs->ch_cfg); |
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priv->mode = mode; |
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debug("%s: regs=%p, mode=%d\n", __func__, priv->regs, priv->mode); |
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return 0; |
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} |
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13. Implement claim_bus() |
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This is where a client wants to make use of the bus, so claims it first. |
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At this point we need to make sure everything is set up ready for data |
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transfer. Note that this function is wholly internal to the driver - at |
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present the SPI uclass never calls it. |
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Here again we look at the old claim function and see some code that is |
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needed. It is anything unrelated to speed and mode: |
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static int exynos_spi_claim_bus(struct udevice *bus) |
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{ |
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struct exynos_spi_priv *priv = dev_get_priv(bus); |
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exynos_pinmux_config(priv->periph_id, PINMUX_FLAG_NONE); |
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spi_flush_fifo(priv->regs); |
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writel(SPI_FB_DELAY_180, &priv->regs->fb_clk); |
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return 0; |
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} |
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The spi_flush_fifo() function is in the removed part of the code, so we |
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need to expose it again (perhaps with an #endif before it and '#if 0' |
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after it). It only needs access to priv->regs which is why we have |
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passed that in: |
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/** |
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* Flush spi tx, rx fifos and reset the SPI controller |
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* |
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* @param regs Pointer to SPI registers |
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*/ |
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static void spi_flush_fifo(struct exynos_spi *regs) |
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{ |
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clrsetbits_le32(®s->ch_cfg, SPI_CH_HS_EN, SPI_CH_RST); |
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clrbits_le32(®s->ch_cfg, SPI_CH_RST); |
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setbits_le32(®s->ch_cfg, SPI_TX_CH_ON | SPI_RX_CH_ON); |
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} |
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14. Implement release_bus() |
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This releases the bus - in our example the old code in spi_release_bus() |
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is a call to spi_flush_fifo, so we add: |
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static int exynos_spi_release_bus(struct udevice *bus) |
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{ |
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struct exynos_spi_priv *priv = dev_get_priv(bus); |
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spi_flush_fifo(priv->regs); |
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return 0; |
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} |
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15. Implement xfer() |
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This is the final method that we need to create, and it is where all the |
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work happens. The method parameters are the same as the old spi_xfer() with |
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the addition of a 'struct udevice' so conversion is pretty easy. Start |
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by copying the contents of spi_xfer() to your new xfer() method and proceed |
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from there. |
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If (flags & SPI_XFER_BEGIN) is non-zero then xfer() normally calls an |
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activate function, something like this: |
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void spi_cs_activate(struct spi_slave *slave) |
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{ |
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struct exynos_spi_slave *spi_slave = to_exynos_spi(slave); |
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/* If it's too soon to do another transaction, wait */ |
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if (spi_slave->bus->deactivate_delay_us && |
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spi_slave->last_transaction_us) { |
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ulong delay_us; /* The delay completed so far */ |
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delay_us = timer_get_us() - spi_slave->last_transaction_us; |
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if (delay_us < spi_slave->bus->deactivate_delay_us) |
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udelay(spi_slave->bus->deactivate_delay_us - delay_us); |
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} |
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clrbits_le32(&spi_slave->regs->cs_reg, SPI_SLAVE_SIG_INACT); |
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debug("Activate CS, bus %d\n", spi_slave->slave.bus); |
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spi_slave->skip_preamble = spi_slave->mode & SPI_PREAMBLE; |
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} |
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The new version looks like this: |
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static void spi_cs_activate(struct udevice *dev) |
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{ |
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struct udevice *bus = dev->parent; |
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struct exynos_spi_platdata *pdata = dev_get_platdata(bus); |
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struct exynos_spi_priv *priv = dev_get_priv(bus); |
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|
||||
/* If it's too soon to do another transaction, wait */ |
||||
if (pdata->deactivate_delay_us && |
||||
priv->last_transaction_us) { |
||||
ulong delay_us; /* The delay completed so far */ |
||||
delay_us = timer_get_us() - priv->last_transaction_us; |
||||
if (delay_us < pdata->deactivate_delay_us) |
||||
udelay(pdata->deactivate_delay_us - delay_us); |
||||
} |
||||
|
||||
clrbits_le32(&priv->regs->cs_reg, SPI_SLAVE_SIG_INACT); |
||||
debug("Activate CS, bus '%s'\n", bus->name); |
||||
priv->skip_preamble = priv->mode & SPI_PREAMBLE; |
||||
} |
||||
|
||||
All we have really done here is change the pointers and print the device name |
||||
instead of the bus number. Other local static functions can be treated in |
||||
the same way. |
||||
|
||||
|
||||
16. Set up the per-child data and child pre-probe function |
||||
|
||||
To minimise the pain and complexity of the SPI subsystem while the driver |
||||
model change-over is in place, struct spi_slave is used to reference a |
||||
SPI bus slave, even though that slave is actually a struct udevice. In fact |
||||
struct spi_slave is the device's child data. We need to make sure this space |
||||
is available. It is possible to allocate more space that struct spi_slave |
||||
needs, but this is the minimum. |
||||
|
||||
U_BOOT_DRIVER(exynos_spi) = { |
||||
... |
||||
.per_child_auto_alloc_size = sizeof(struct spi_slave), |
||||
} |
||||
|
||||
|
||||
17. Optional: Set up cs_info() if you want it |
||||
|
||||
Sometimes it is useful to know whether a SPI chip select is valid, but this |
||||
is not obvious from outside the driver. In this case you can provide a |
||||
method for cs_info() to deal with this. If you don't provide it, then the |
||||
device tree will be used to determine what chip selects are valid. |
||||
|
||||
Return -ENODEV if the supplied chip select is invalid, or 0 if it is valid. |
||||
If you don't provide the cs_info() method, -ENODEV is assumed for all |
||||
chip selects that do not appear in the device tree. |
||||
|
||||
|
||||
18. Test it |
||||
|
||||
Now that you have the code written and it compiles, try testing it using |
||||
the 'sf test' command. You may need to enable CONFIG_CMD_SF_TEST for your |
||||
board. |
||||
|
||||
|
||||
19. Prepare patches and send them to the mailing lists |
||||
|
||||
You can use 'tools/patman/patman' to prepare, check and send patches for |
||||
your work. See the README for details. |
Loading…
Reference in new issue