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QSPI U-Boot support
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------------------
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Host processor is connected to serial flash device via qpsi
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interface. QSPI is a kind of spi module that allows single,
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dual and quad read access to external spi devices. The module
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has a memory mapped interface which provide direct interface
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for accessing data form external spi devices.
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The one QSPI in the device is primarily intended for fast booting
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from Quad SPI flash devices.
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Usecase
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-------
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MLO/u-boot.img will be flashed from SD/MMC to the flash device
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using serial flash erase and write commands. Then, switch settings
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will be changed to qspi boot. Then, the ROM code will read MLO
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from the predefined location in the flash, where it was flashed and
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execute it after storing it in SDRAM. Then, the MLO will read
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u-boot.img from flash and execute it from SDRAM.
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SPI mode
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SPI mode uses mtd spi framework for transfer and reception of data.
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Can be used in:
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1. Normal mode: use single pin for transfers
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2. Dual Mode: use two pins for transfers.
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3. Quad mode: use four pin for transfer
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Memory mapped read mode
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-----------------------
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In this, SPI controller is configured using configuration port and then
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controler is switched to memory mapped port for data read.
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Driver
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------
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drivers/qspi/ti_qspi.c
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- Newly created file which is responsible for configuring the
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qspi controller and also for providing the low level api which
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is responsible for transferring the datas from host controller
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to flash device and vice versa.
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Testing
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-------
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A seperated file named README.dra_qspi_test has been created which gives all the
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details about the commands required to test qspi at U-Boot level.
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