Mapping between bootpart taken from EXT_CSD_EXTRACT_BOOT_PART() and
Partition Access bits used by the mmc_switch_part() function may be quite
misleading. So add extended comment describing why in sunxi case is this
mapping just a simple identity. Because in generic case this mapping
requires non-trivial mapping table.
Signed-off-by: Pali Rohár <p...@kernel.org>
---
arch/arm/mach-sunxi/board.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/arch/arm/mach-sunxi/board.c b/arch/arm/mach-sunxi/board.c
index 391a65a5495f..73519f6262ec 100644
--- a/arch/arm/mach-sunxi/board.c
+++ b/arch/arm/mach-sunxi/board.c
@@ -381,7 +381,17 @@ static bool sunxi_valid_emmc_boot(struct mmc *mmc)
(mmc->ext_csd[EXT_CSD_BOOT_BUS_WIDTH] & 0x1b) != 0x09)
return false;
- /* Partition 0 is the user data partition, bootpart must be 1 or 2. */
+ /*
+ * bootpart == 0 means that eMMC booting is disabled.
+ * bootpart == 1 or 2 means to boot from Boot Partition 1 or 2.
+ * bootpart == 7 means to boot from User Area.
+ * Other bootpart values are reserved.
+ * mmc_switch_part() takes partition access value which is:
+ * 0 for User Area; 1-2 for Boot Partition 1-2; 3 for RPMB; 4-7 for GP
1-4.
+ * We allow booting only from Boot Partition 1 or 2 so
+ * bootpart mapping between EXT_CSD_EXTRACT_BOOT_PART()
+ * and mmc_switch_part() is straightforward identity.
+ */
if (bootpart != 1 && bootpart != 2)
return false;
--
2.20.1
