On 10/23/21 20:18, Matthew Brost wrote:
On Sat, Oct 23, 2021 at 07:46:48PM +0200, Thomas Hellström wrote:
On 10/22/21 20:09, John Harrison wrote:
And to be clear, the engine reset is not supposed to fail. Whether
issued by GuC or i915, the GDRST register is supposed to self clear
according to the bspec. If we are being sent the G2H notification for an
engine reset failure then the assumption is that the hardware is broken.
This is not a situation that is ever intended to occur in a production
system. Therefore, it is not something we should spend huge amounts of
effort on making a perfect selftest for.
I don't agree. Selftests are there to verify that assumptions made and
contracts in the code hold and that hardware behaves as intended / assumed.
No selftest should ideally trigger in a production driver / system. That
doesn't mean we can remove all selftests or ignore updating them for altered
assumptions / contracts. I think it's important here to acknowledge the fact
that this and the perf selftest have found two problems that need
consideration for fixing for a production system.
I'm confused - we are going down the rabbit hole here.
Back to this patch. This test was written for very specific execlists
behavior. It was updated to also support the GuC. In that update we
missed fixing the failure path, well because it always passed. Now it
has failed, we see that it doesn't fail gracefully, and takes down the
machine. This patch fixes that. It also openned my eyes to the horror
show reset locking that needs to be fixed long term.
Well the email above wasn't really about the correctness of this
particular patch (I should probably have altered the subject to reflect
that) but rather about the assumption that failures that should never
occur in a production system are not worth spending time on selftests for.
For the patch itself, I'll take a deeper look at the patch and get back.
/Thomas
