[PATCH] drm/atomic: Convert a warning to dbg atomic printk

[Zack Rusin]

On Wed, 2022-04-06 at 10:30 +0200, Michel Dänzer wrote:
> ⚠ External Email
> 
> On 2022-04-06 00:47, Zack Rusin wrote:
> > On Tue, 2022-04-05 at 19:09 +0200, Michel Dänzer wrote:
> > > On 2022-04-04 20:21, Zack Rusin wrote:
> > > > From: Zack Rusin <zackr at vmware.com>
> > > > 
> > > > By default each flip times out after 0.1 sec
> > > 
> > > 10 * HZ is 10 seconds, not 0.1.
> > 
> > Yea, sorry, this entire commit message is not correct. I've sent
> > out a
> > very old diff with a log the best I could remember. I recall our
> > conversation now and iirc we said that maybe an interface through
> > drm
> > atomic code to enable/disable this error is the way to go but after
> > looking at this again I'm not sure. More below.
> > 
> > > > and a warning about the time out is added to the kernel log.
> > > > The
> > > > warning is
> > > > harmless because there's another flip coming right after but it
> > > > can
> > > > quickly fill up
> > > > the log, e.g. missing 2 flips every second over a 24 hour span
> > > > will
> > > > add about 172 thousand lines to the log.
> > > 
> > > As we discussed before, while this might be true for the vmwgfx
> > > driver,
> > > for other drivers this message indicates that either the GPU
> > > hung, or
> > > something else went wrong spectacularly. As such, I think we do
> > > want to
> > > see these messages by default for other drivers at least.
> > 
> > I'm not going to argue for or against that but I am curious what's
> > the
> > point of the message. The message is basically saying "something
> > could
> > possibly have went very wrong". OK, what's next? Especially if
> > there's
> > no visible problems and it's not reproducible. Even if it would be
> > reproducible there's nothing actionable from the message itself. If
> > the
> > system has no output connected and no users are currently logged in
> > and
> > we missed a flip, does it matter?
> 
> I don't think waiting for a 10 second timeout is the appropriate
> behaviour in that case. While a KMS CRTC is enabled, the driver needs
> to make it work, in the worst case via a timer which ticks at the
> CRTC refresh rate.

What if it isn't a driver bug and it just so happens that vmwgfx is the
only one that's running on some specific system without a display long
enough? Without being able to reproduce how would you know?

> 
> The error means that either:
> 
> * A flip actually didn't complete in 10 seconds.
> * There's some kind of time tracking issue which results in the timer
> firing after less than 10 seconds (of the system actually running).
> 
> Either way, it's an issue which should be fixed rather than just
> swept under the rug.

Without being able to reproduce or really confirm that it's an actual
problem in vmwgfx I'm going to leave this to you then. I'd be happy to
look at it again or help out in any way I can if you find any problems
we can do anything about.

z