[U-Boot] arm: socfpga gen5: warm reboot reliability

[Simon Goldschmidt]

Hi,

[This whole description is not qspi specific but qspi happens to be my 
boot source. It should be the same when booting from mmc or nand.]

On my socfgpa gen5 board, I was a little surprised that a soft reboot 
did not start the SPL from qspi after updating it from a running Linux 
(via swupdate writing to qspi).

When debugging this, I found that this is because SPL and U-Boot set the 
magic value 0xae9efebc to the sysmgr_regs->romcodegrp_warmramgrp_enable 
register, which tells the boot ROM that it can jump to SPL in OnChip RAM 
on next warm reboot.

Now this is a problem for me specifically because I want to run the SPL 
stored in qspi after updating it. I don't know if I'm the only one 
wanting to do that, but I could implement this for my own board by just 
resetting the magic value in the warmramgrp_enable register.

What surprised me more is that the boot ROM provides the ability to 
check the CRC of SPL, but it doesn't check the CRC since the related 
registers tellt it to not do that (to enable this, SPL would have to 
write its length + CRC to sysmgr registers). I would have suspected this 
bad design since maybe we were rebooted by the watchdog because some 
driver wrote bad data somewhere, so it might well be the SPL in OnChip 
RAM is not intact any more.

Now should we:
a) calculate and set a CRC for SPL's text / rodata segments (what about 
initialized rwdata?) or
b) set the warmramgrp_enable register to always load SPL from boot source or
c) make it configurable?

Writing the code for any of the 3 choices is easy, so I wanted to get an 
opinion first before sending a patch. Personally, I'd favour always 
loading SPL from boot source, but the comment (in misc_gen5.c 
arch_early_init_r()) suggests I'd break ancient kernels with that (I 
assume the problem is the problem I have with 4.9: Linux sets qspi into 
4-byte mode and the boot rom can then not load SPL since it uses 3-byte 
mode without switching mode in the qspi chip).

Any thoughts?

Simon