[RFC PATCH 0/3] fastboot: sunxi: Determine MMC device at runtime

Andre Przywara andre.przywara at arm.com
Mon May 24 02:36:47 CEST 2021

At the moment the fastboot code relies on the Kconfig variable
CONFIG_FASTBOOT_FLASH_MMC_DEV to point to the MMC device to use for the
flash command. This value needs to be the *U-Boot device number*, which
is picked by the U-Boot device model at runtime. This makes it quite
tricky and fragile to fix this variable at compile time, as other DT
nodes and aliases influence the enumeration process.

To make this process more robust, allow the device number to be picked at
runtime, which sounds like a better fit to find this device number. Patch
1/3 introduces a weak function for that purpose.
Patch 2/3 then implements this function for the Allwinner platform. The
code follows the idea behind the existing Kconfig defaults: Use the eMMC
device, if that exists, or the SD card otherwise. This patch is actually
not sunxi specific, so might be adopted by other platforms as well.
Patch 3/3 then drops the existing Kconfig defaults for sunxi, to clean
this up and remove the implicit assumption that the eMMC device is always
device 1 (as least for the fastboot code).

I would be curious if others think this is the right way forward.
The fact that the U-Boot device numbers are determined at runtime
seems to conflict with the idea of a Kconfig variable in the first place,
hence this series. This brings us one step closer to the end goal of
removing the "eMMC is device 1" assumption.

I am looking forward to any comments on this series!


Andre Przywara (3):
  fastboot: Allow runtime determination of MMC device
  sunxi: Implement fastboot_get_mmc_device()
  sunxi: Drop sunxi FASTBOOT_FLASH_MMC_DEV defaults

 board/sunxi/board.c           | 37 +++++++++++++++++++++++++++++++++++
 drivers/fastboot/Kconfig      |  4 +---
 drivers/fastboot/fb_command.c |  6 +++---
 drivers/fastboot/fb_common.c  |  3 ++-
 drivers/fastboot/fb_mmc.c     | 12 ++++++++----
 include/fastboot.h            |  7 +++++++
 6 files changed, 58 insertions(+), 11 deletions(-)


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