[U-Boot] ARM: sama5d2: Implement boot device autodetection

[Andreas Bießmann]

On Fri, Apr 22, 2016 at 09:56:21PM +0200, Marek Vasut wrote:
> Implement support for saving ARM register R4 early during boot using
> save_boot_params . Implement support for decoding the stored register
> R4 value in spl_boot_device() to obtain boot device from which the
> SoC booted. This way, the SPL will always load U-Boot from the same
> device from which the SPL itself booted instead of using hard-coded
> boot device.
> 
> This functionality is useful for example when booting sama5d2-xplained
> from SD card, where by default the SPL would try loading the U-Boot
> from eMMC and fail. This is because eMMC is on SDHCI0 (BOOT_DEVICE_MMC1),
> while SD slot is on SDHCI1 (BOOT_DEVICE_MMC2) and the SPL was hard-wired
> to always boot from BOOT_DEVICE_MMC1.
> 
> Signed-off-by: Marek Vasut <marex at denx.de>
> Cc: Andreas Bießmann <andreas.devel at googlemail.com>
> Cc: Wenyou Yang <wenyou.yang at atmel.com>
>

Reviewed-by: Andreas Bießmann <andreas at biessmann.org>

> ---
>  arch/arm/mach-at91/Makefile               |  2 +-
>  arch/arm/mach-at91/bootparams_atmel.S     | 18 ++++++++++++++++
>  arch/arm/mach-at91/include/mach/sama5d2.h | 12 +++++++++++
>  arch/arm/mach-at91/spl.c                  | 36 +++++++++++++++++++++++++++++++
>  4 files changed, 67 insertions(+), 1 deletion(-)
>  create mode 100644 arch/arm/mach-at91/bootparams_atmel.S