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------------------------------------------------------------------------
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A3M071 board support
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------------------------------------------------------------------------
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SPL NOR flash support:
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----------------------
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To boot fast into the OS (Linux), this board port integrates the SPL
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framework. This means, that a special, stripped-down version of
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U-Boot runs in the beginning. In the case of the A3M071 board, this
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SPL U-Boot version is less than 16 KiB big. This SPL U-Boot can either
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boot the OS (Linux) or a "real", full-blown U-Boot. This detection
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on whether to boot Linux or U-Boot is done by using the "boot_os"
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environment variable. If "boot_os" is set to "yes", Linux will be
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loaded and booted from the SPL U-Boot version. Otherwise, the
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full-blown U-Boot version will be loaded and run.
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Enabling Linux booting:
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-----------------------
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From U-Boot:
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=> setenv boot_os yes
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=> saveenv
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From Linux:
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$ fw_setenv boot_os yes
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Enabling U-Boot booting:
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------------------------
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From U-Boot:
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=> setenv boot_os no
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=> saveenv
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From Linux:
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$ fw_setenv boot_os no
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Preparing Linux image(s) for booting from SPL U-Boot:
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-----------------------------------------------------
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To boot the Linux kernel from the SPL, the DT blob (fdt) needs to get
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prepard/patched first. U-Boot usually inserts some dynamic values into
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the DT binary (blob), e.g. autodetected memory size, MAC addresses,
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clocks speeds etc. To generate this patched DT blob, you can use
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the following command:
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1. Load fdt blob to SDRAM:
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=> tftp 1800000 a3m071/a3m071.dtb
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2. Set bootargs as desired for Linux booting (e.g. flash_mtd):
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=> run mtdargs addip2 addtty
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3. Use "fdt" commands to patch the DT blob:
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=> fdt addr 1800000
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=> fdt boardsetup
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=> fdt chosen
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4. Display patched DT blob (optional):
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=> fdt print
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5. Save fdt to NOR flash:
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=> erase fc180000 fc07ffff
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=> cp.b 1800000 fc180000 10000
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All this can be integrated into an environment command:
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=> setenv upd_fdt 'tftp 1800000 a3m071/a3m071.dtb;run mtdargs addip addtty; \
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fdt addr 1800000;fdt boardsetup;fdt chosen;erase fc180000 fc07ffff; \
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cp.b 1800000 fc180000 10000'
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=> saveenv
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After this, only "run upd_fdt" needs to get called to load, patch
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and save the DT blob into NOR flash.
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Additionally, the Linux kernel image has to be saved uncompressed in
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its uImage file (and not gzip compressed). This can be done with this
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command:
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$ mkimage -A ppc -O linux -T kernel -C none -a 0 -e 0 \
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-n "Linux Kernel Image" -d vmlinux.bin uImage.uncompressed
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------------------------------------------------------------------------
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Stefan Roese, 2012-08-23
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