[Skiboot] [PATCH] phb3: Continue CAPP setup even if PHB is already in CAPP mode

[Michael Neuling]

On Thu, 2015-08-13 at 14:40 +1000, Daniel Axtens wrote:
> This fixes a critical bug in CAPI support.
> 
> CAPI requires that all faults are escalated into a fence, not a
> freeze. This is done by setting bits in a number of MMIO
> registers. phb3_set_capi_mode() calls phb3_init_capp_errors() to do
> this. However, if the PHB is already in CAPP mode - for example in the
> recovery case - phb3_set_capi_mode() will bail out early, and those
> registers will not be set.
> 
> This is quite easy to verify. PCI config space access errors, for
> example, normally cause a freeze. On a CAPI-mode PHB, they should
> cause a fence. Say we have a CAPI card on PHB 0, and we inject a
> PCI config space error:
> 
> echo 0x8000000000000000 > /sys/kernel/debug/powerpc/PCI0000/err_injct_inboundA;
> lspci;
> 
> The first time we inject this, the PHB will fence and recover, but
> won't reset the registers. Therefore, the second time we inject it,
> we will incorrectly freeze, not fence.
> 
> Worse, the recovery for the resultant EEH freeze event interacts
> poorly with the CAPP, triggering an EEH recovery of the PHB. The
> combination of the two attempted recoveries will get the PHB into
> an inoperable state.
> 
> It's quite likely that there other side effects of bailing out
> early. For example, the timebase sync probably fails to recover.
> Rather than auditing all the possibilities, I verified that
> repeating the entire setup procedure still works when the PHB is
> already in CAPP mode. It does work, so just do the entire setup
> every time instead of bailing out early.
> 
> Signed-off-by: Daniel Axtens <dja at axtens.net>

Acked-By: Michael Neuling <mikey at neuling.org>

> ---
>  hw/phb3.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/hw/phb3.c b/hw/phb3.c
> index cdc20e8b0ed4..ba584c914f46 100644
> --- a/hw/phb3.c
> +++ b/hw/phb3.c
> @@ -3268,7 +3268,6 @@ static int64_t phb3_set_capi_mode(struct phb *phb, uint64_t mode,
>  	xscom_read(p->chip_id, 0x9013c03, &reg);
>  	if (reg & PPC_BIT(0)) {
>  		PHBDBG(p, "CAPP: Already in CAPP mode\n");
> -		return OPAL_SUCCESS;
>  	}
>  
>  	/* poll cqstat */