[PATCH 5/7] compositor-drm: Gracefully handle vblank and flip invalid timestamps

[Miguel Angel Vico]

Hi,

On Tue, 22 Mar 2016 09:30:51 +0000
Daniel Stone <daniel at fooishbar.org> wrote:

> Hi,
> 
> On 22 March 2016 at 08:50, Daniel Vetter <daniel at ffwll.ch> wrote:
> > On Tue, Mar 22, 2016 at 08:47:12AM +0000, Daniel Stone wrote:  
> >> This is odd. Instant queries failing is fine, but in which
> >> circumstances can you fail to return a valid timestamp in a
> >> pageflip event ... ? I don't know of any other kernel driver which
> >> does this - at the very least, if you don't have a hardware
> >> timestamp, then you log the time in your kernel driver which
> >> handles the hardware event (e.g. softirq handler), and use that
> >> instead.  
> >
> > nouveau bugs iirc. Yes, should never happen, it's a bug in the
> > kernel driver that iirc Mario recently tracked down. nouveau
> > somehow started the vblank machinery before the pipe was up, or
> > something like that.
> >
> > So yeah happens, I'm not sure we want to let kernel drivers get
> > away with plain broken behavior forever. I'm leaning towards nack,
> > pls fix the kernel driver.  
> 
> Yes, particularly as no-one has reported it on any other drivers. I
> don't think it's behaviour we really want to support.
> 
> > And maybe make sure the corresponding igt pass ;-)  
> 
> For reference, igt here is intel-gpu-tools, which despite its name is
> actually a generic KMS test/conformance suite. Most of the tests are
> still Intel-specific, but we are actively working on making them
> generic - I was actually in the middle of reviewing a patchset to make
> a rather larger chunk of it generic when I got distracted by this
> thread. ;) It's a great way to find out ways in which your driver
> breaks userspace expectations of a 'well-behaved' KMS driver early.

Thanks guys! We'll fix this in our driver and remove the workaround in
weston.

> 
> Cheers,
> Daniel


-- 
Miguel

NVIDIA GmbH, Wuerselen, Germany, Amtsgericht Aachen, HRB 8361
Managing Director: Karen Theresa Burns

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