[U-Boot] [BUG] am335x: SPL: fails to load u-boot.img from vfat partition on eMMC

[Heiko Schocher]

Hello Stefan,

the am335x based shc board fails loading u-boot.img in SPL from vfat
partition on eMMC card with current HEAD of mainline U-Boot:

U-Boot SPL 2017.01-00294-g0c9e85f (Jan 23 2017 - 11:23:05)
SHC
MPU reference clock runs at 6 MHz
Setting MPU clock to 594 MHz
Enabling Spread Spectrum of 18 permille for MPU
Trying to boot from MMC2
reading u-boot.img
reading u-boot.img

Detected with my weekly tbot tests of U-Boot. An automated
git bisect cycle with tbot shows your patch:

$ git bisect visualize
commit 8d48c92b45aea91e2a2be90f2ed93677e85526f1
Author: Stefan Brüns <stefan.bruens at rwth-aachen.de>
Date:   Sat Dec 17 03:55:10 2016 +0100

     fs/fat: simplify get_fatent for FAT12

     Instead of shuffling bits from two adjacent 16 bit words, use one 16 bit
     word with the appropriate byte offset in the buffer.

     Signed-off-by: Stefan Brüns <stefan.bruens at rwth-aachen.de>

$ git bisect log
git bisect start
# bad: [0c9e85f67cd86d2d7a3424ea3ebff0e6db7a3915] Merge branch 'master' of 
git://git.denx.de/u-boot-uniphier
git bisect bad 0c9e85f67cd86d2d7a3424ea3ebff0e6db7a3915
# good: [0c1d74fda7c0063eeca4d8d9fa8674e6ec2ef685] image: Add crypto_algo struct for RSA info
git bisect good 0c1d74fda7c0063eeca4d8d9fa8674e6ec2ef685
# good: [fe9822556e051e6c24a3832532166ade00a81a8c] Merge branch 'master' of 
git://git.denx.de/u-boot-uniphier
git bisect good fe9822556e051e6c24a3832532166ade00a81a8c
# bad: [7876dcb5d46057403a715771a75c483add6a64c1] ARM64: zynqmp: Add missing earlycon for ep108
git bisect bad 7876dcb5d46057403a715771a75c483add6a64c1
# good: [36737f22b78a475c6bbc8a0467b51e4d95b52a7d] Merge git://git.denx.de/u-boot-dm
git bisect good 36737f22b78a475c6bbc8a0467b51e4d95b52a7d
# bad: [8098b8cb3f15c8b203de133106e4bce4b8fe956d] configs: engicam: Enable CONFIG_IMAGE_FORMAT_LEGACY
git bisect bad 8098b8cb3f15c8b203de133106e4bce4b8fe956d
# good: [6c1a808052ba6a875df7aa450b6df4b199f3a281] fs/fat: Avoid corruption of sectors following the FAT
git bisect good 6c1a808052ba6a875df7aa450b6df4b199f3a281
# bad: [3d3a74cc8c774345be7d1661b215555ad41f4515] mmc: move MMC_SDHCI_IO_ACCESSORS to Kconfig
git bisect bad 3d3a74cc8c774345be7d1661b215555ad41f4515
# bad: [3cc5bbb8e68dc67b7c3d2fdebef69408e5271469] fs/ext4: Initialize group descriptor size for 
revision level 0 filesystems
git bisect bad 3cc5bbb8e68dc67b7c3d2fdebef69408e5271469
# bad: [085be482f6c62614ddbe51000a09db9dec360e90] ARM: revive CONFIG_USE_ARCH_MEMCPY/MEMSET for 
UniPhier and Tegra
git bisect bad 085be482f6c62614ddbe51000a09db9dec360e90
# bad: [8d48c92b45aea91e2a2be90f2ed93677e85526f1] fs/fat: simplify get_fatent for FAT12
git bisect bad 8d48c92b45aea91e2a2be90f2ed93677e85526f1
# good: [b8948d2aef80717d3d2c4f37ec086ce3ea5ad24f] fs/fat: merge readwrite get_fatent_value() with 
readonly get_fatent()
git bisect good b8948d2aef80717d3d2c4f37ec086ce3ea5ad24f
# first bad commit: [8d48c92b45aea91e2a2be90f2ed93677e85526f1] fs/fat: simplify get_fatent for FAT12

Reverting this patch, and it works as expected:
U-Boot SPL 2017.01-00294-g0c9e85f-dirty (Jan 23 2017 - 12:53:29)
SHC
MPU reference clock runs at 6 MHz
Setting MPU clock to 594 MHz
Enabling Spread Spectrum of 18 permille for MPU
Trying to boot from MMC2
reading u-boot.img
reading u-boot.img


U-Boot 2017.01-00294-g0c9e85f-dirty (Jan 23 2017 - 12:53:29 +0100)

CPU  : AM335X-GP rev 2.1
I2C:   ready
DRAM:  512 MiB
MMC:   OMAP SD/MMC: 0, OMAP SD/MMC: 1
Net:   cpsw
Enter 'shc' to enter prompt (times out) 0
Enter 'noautoboot' to enter prompt without timeout
U-Boot#


Any ideas what could be wrong here?

Thanks!

bye,
Heiko
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