Re: [Intel-gfx] [PATCH] drm/i915: make user mode sync polarity setting explicit

[Imre Deak <imre.deak@intel.com>]

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On Tue, 2013-07-30 at 11:57 +0100, Chris Wilson wrote:
> On Tue, Jul 30, 2013 at 01:36:32PM +0300, Imre Deak wrote:
> > Userspace can pass a mode with an unspecified vsync/hsync polarity
> > setting. All encoders in the Intel driver take this to mean a negative
> > polarity setting. The HW readout/state checker code on the other hand
> > needs these flags to be explicitly set, otherwise the state checker will
> > WARN about the mismatch.
> > 
> > Get rid of the WARN by making the polarity setting explicit in the
> > adjusted mode flags based on the requested mode flags. This will keep
> > the existing behavior otherwise.
> > 
> > Note that we could guess from the other timing parameters whether the
> > user wanted a VESA or other standard mode and set the polarity
> > accordingly. This is what the NV driver does
> > (drivers/gpu/drm/nouveau/dispnv04/crtc.c), but I think that's not very
> > exact and would change the existing behavior of the Intel driver.
> 
> Right, don't guess. If the user wanted the standard mode, then the flags
> would have been taken from the standard modeline.
>  
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=65442
> 
> You can add a tested-by here for qa.

Tested-by: Cancan Feng <cancan.feng@intel.com>
 
> > Signed-off-by: Imre Deak <imre.deak@intel.com>
> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

CC'ing people who might be interested.

After some discussion with Ville, we could refine this further at the
drm core level by enforcing the Intel behavior - defaulting to negative
polarity and also checking/sanitizing the PHSYNC/PVSYNC flags.
PHSYNC/PVSYNC isn't used by the Intel driver so we could still go with
the above patch for now and follow-up with a drm core fix.

We should probably also reject modes at drm core level where both
positive and negative flags are set, again in a separate follow-up
patch.

--Imre

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