[U-Boot] BeagleboneBlack vboot from SPI flash difficulties

[Joe Desbonnet]

I've been trying to implement vboot from SPI flash on the BeagleBone Black
with only limited success. I'm working with u-boot 2016.07 and using the
instructions in beaglebone_vboot.txt (in doc directory).

So far: I've had no problem booting regular u-boot from SPI flash. I build
with  am335x_boneblack_defconfig with minor modifications: added SPI_BOOT
to the list of items on CONFIG_SYS_EXTRA_OPTIONS and added
CONFIG_SPI_FLASH_STMICRO=y to enable support for my SPI flash chip
(M25P16). The I use the following command sequence from the u-boot command
line to program the flash:

sf probe 0
sf erase 0 +80000
mmc rescan
fatload mmc 0 ${loadaddr} MLO.byteswap
sf write ${loadaddr} 0 ${filesize}
fatload mmc 0 ${loadaddr} u-boot.img
sf write ${loadaddr} 0x20000 ${filesize}

And this works nicely.

I also have had success with vboot enabled u-boot using
the beaglebone_vboot.txt instructions and booting from SD card.

*BUT*

when I copy MLO(.byteswap) and u-boot.img that works successfully on SD
card to SPI flash it fails to get past the Second Phase Loader:

U-Boot SPL 2016.07 (Aug 10 2016 - 16:06:39)
Trying to boot from SPI

U-Boot SPL 2016.07 (Aug 10 2016 - 16:06:39)
Trying to boot from SPI

... etc for ever

On an oscilloscope I can see what I'm sure is the SPL trying to loading
u-boot.img on the SPI bus. But it never gets as far as executing it.

So in summary, I've got SPI boot working and vboot working but I cannot
seem to combine both.

Any ideas what I'm doing wrong?

Thanks,