Re: [PATCH 1/4] drm/i915: don't warn if IRQs are disabled when shutting down display IRQs

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, Jul 14, 2014 at 11:56:57AM -0300, Paulo Zanoni wrote:
> 2014-07-07 18:53 GMT-03:00 Jesse Barnes <jbarnes@virtuousgeek.org>:
> > On Mon, 7 Jul 2014 18:48:47 -0300
> > Paulo Zanoni <przanoni@gmail.com> wrote:
> >
> >> (documenting what we discussed on IRC)
> >>
> >> 2014-06-20 13:29 GMT-03:00 Jesse Barnes <jbarnes@virtuousgeek.org>:
> >> > This was always the case on our suspend path, but it was recently
> >> > exposed by the change to use our runtime IRQ disable routine rather than
> >> > the full DRM IRQ disable.  Keep the warning on the enable side, as that
> >> > really would indicate a bug.
> >>
> >> While I understand the patch and think it's a reasonable thing to do,
> >> I feel the need to spend some time persuading you in replacing it with
> >> something that doesn't involve removing WARNs from our driver. While
> >> the driver is runtime suspended, no one should really be manipulating
> >> IRQs, even if they're disabling stuff that is already disabled: this
> >> reflects there's probably a problem somewhere. These WARNs are
> >> extremely helpful for the runtime PM feature because almost nobody
> >> actually uses runtime PM to notice any bugs with it, so the WARNs can
> >> make QA report bugs and bisect things for us.
> >>
> >> Also, it seems S3 suspend is currently a little disaster on our
> >> driver. Your 6 patches just solve some of the WARNs, not all of them.
> >> And last week I even solved another WARN on the S3 path. I just did
> >> some investigation, and the current bad commits are:
> >> 8abdc17941c71b37311bb93876ac83dce58160c8,
> >> e11aa362308f5de467ce355a2a2471321b15a35c and
> >> 85e90679335f56d162f4a0ff525573818e17ce44. If I just revert these 3
> >> commits, S3 doesn't give me any WARNs.
> >>
> >> Instead of the change you proposed, can't we think of another solution
> >> that would maybe address all the 3 regressions we have? Since we're
> >> always submitting patches to change the order we do things at S3
> >> suspend/resume, shouldn't we add something like "dev_priv->suspending"
> >> that could be used to avoid the strict ordering that is required
> >> during runtime?
> >
> > Hm I was running with those changes and didn't see additional warnings,
> > so I'll have to look again.
> >
> > I agree we want sensible warnings in place, and maybe removing this one
> > is too permissive, but I'd like to avoid a suspending flag if we can.
> >
> > Maybe we just need to bundle up our assertions and check all the
> > relevant state after runtime suspend or S3 like we do for mode set
> > state in various places.  That would let us keep our warnings, but also
> > save us from having them spread out in code paths that get used in
> > many different contexts.
> 
> I'm probably going to regret this, but since no one proposed a better
> patch and the bug is still there:
> Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>

Not really eager to merge a patch soaking in preemptive regrets ...

I'll punt on this for now.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch