Re: [PATCH] PCI: pciehp: Ignore Link Down/Up caused by DPC

[Lukas Wunner <lukas@wunner.de>]

On Thu, Apr 29, 2021 at 07:29:59PM +0800, Yicong Yang wrote:
> On 2021/4/28 22:40, Lukas Wunner wrote:
> > If DPC doesn't recover within 3 seconds, pciehp will consider the
> > error unrecoverable and bring down the slot, no matter what.
> > 
> > I can't tell you why DPC is unable to recover.  Does it help if you
> > raise the timeout to, say, 5000 msec?
> 
> I raise the timeout to 4s and it works well. I dump the remained jiffies in
> the log and find sometimes the recovery will take a bit more than 3s:

Thanks for testing.  I'll respin the patch and raise the timeout
to 4000 msec.

The 3000 msec were chosen arbitrarily.  I couldn't imagine that
it would ever take longer than that.  The spec does not seem to
mandate a time limit for DPC recovery.  But we do need a timeout
because the DPC Trigger Status bit may never clear and then pciehp
would wait indefinitely.  This can happen if dpc_wait_rp_inactive()
fails or perhaps because the hardware is buggy.

I'll amend the patch to clarify that the timeout is just a reasonable
heuristic and not a value provided by the spec.

Which hardware did you test this on?  Is this a HiSilicon platform
or Intel?

Thanks!

Lukas