[Skiboot] [RESEND][PATCH] phb4: Don't probe a PHB if its garded

[Stewart Smith]

Vaibhav Jain <vaibhav at linux.ibm.com> writes:
> Presently phb4_probe_stack() causes an exception while trying to probe
> a PHB if its garded. This causes skiboot to go into a reboot loop with
> following exception log:
>
>  ***********************************************
>  Fatal MCE at 000000003006ecd4   .probe_phb4+0x570
>  CFAR : 00000000300b98a0
>  <snip>
>  Aborting!
> CPU 0018 Backtrace:
>  S: 0000000031cc37e0 R: 000000003001a51c   ._abort+0x4c
>  S: 0000000031cc3860 R: 0000000030028170   .exception_entry+0x180
>  S: 0000000031cc3a40 R: 0000000000001f10 *
>  S: 0000000031cc3c20 R: 000000003006ecb0   .probe_phb4+0x54c
>  S: 0000000031cc3e30 R: 0000000030014ca4   .main_cpu_entry+0x5b0
>  S: 0000000031cc3f00 R: 0000000030002700   boot_entry+0x1b8
>
> This is caused as phb4_probe_stack() will ignore all xscom read/write
> errors to enable PHB Bars and then tries to perform an mmio to read
> PHB Version registers that cause the fatal MCE.
>
> We fix this by ignoring the PHB probe if the first xscom_write() to
> populate the PHB Bar register fails, which indicates that there is
> something wrong with the PHB.
>
> Cc: stable
> Fixes: dc21b4db3a2e('hw/phb4: Add initial support')
> Reviewed-by: Oliver O'Halloran <oohall at gmail.com>
> Signed-off-by: Vaibhav Jain <vaibhav at linux.ibm.com>

Thanks! Merged to master as of 1520d6a1e3aaec74228d213083b68da70729121a
and to 6.0.x as of 54ac06ff404bf13d0a8035985ff67e0610213f5a.

-- 
Stewart Smith
OPAL Architect, IBM.