Re: [PATCH v2] drm/i915: Use crtc_state->has_psr instead of CAN_PSR for pipe update

[Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>]

On Mon, 2018-07-09 at 11:16 -0700, Tarun Vyas wrote:
> On Mon, Jul 09, 2018 at 11:30:00AM -0700, Dhinakaran Pandiyan wrote:
> > 
> > On Sun, 2018-07-08 at 18:46 -0700, Tarun Vyas wrote:
> > > 
> > > In commit "drm/i915: Wait for PSR exit before checking for vblank
> > > evasion", the idea was to limit the PSR IDLE checks when PSR is
> > > actually supported. While CAN_PSR does do that check, it doesn't
> > > applies on a per-crtc basis. crtc_state->has_psr is a more
> > > granular
> > > check that avoids everything but pipe A, for the PSR IDLE check.
> > > 
> > > With this, the PSR IDLE check should be a *no-op* for all but
> > > pipe A
> > > which is what was intended originally.
> > > 
> > So, the problem is when we update a non-PSR pipe (B or C) and PSR
> > is
> > active on another pipe(A, specifically), we end up waiting for the
> > pipe
> > A MMIO to become idle.
> > 
> > Can you please update the commit message as the commit message
> > makes
> > the per-pipe check sound like an optimization? 
> > 
> > This also points to a gap in our testing, I don't see a two pipe
> > PSR
> > related IGT.
> > 
> That's right. On my KBL chromebook that's running the drm-tip, when I
> plug-in an external display, so pipe B,
> I see "[drm:intel_pipe_update_start] *ERROR* PSR idle timed out,
> atomic update may fail on pipe B", Iadded the pipe
> name in the DRM_ERROR, may be I should make that change in the v3 of
> this patch along with updating the commit message.
> 
> But, yea, this proves that with the CAN_PSR check, the non-PSR pipes
> (B/C) wait on pipe-A to exit PSR which doesn't have
> any reason to do so at that moment, hence the error.
> 
> I'll make the commit message changes and add the pipe name in the
> DRM_ERROR as well ?

I am thinking you could pass crtc_state to intel_psr_wait_for_idle()
and then check inside the implementation if the argument is the same as
the pipe PSR was enabled on and then wait.

intel_psr_wait_for_idle(crtc_state) {
	if (!CAN_PSR() || !crtc_state->has_psr)
		return;
	...
}

I don't like how intel_psr_wait_for_idle() doesn't care which pipe
(transcoder actually) MMIO it should wait on.
		

> > 
> > > 
> > > Fixes: a608987970b9 ("drm/i915: Wait for PSR exit before checking
> > > for
> > > vblank evasion")
> > > 
> > > v2: Remove unnecessary parantheses, make checkpatch happy.
> > > 
> > > Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
> > > Signed-off-by: Tarun Vyas <tarun.vyas@intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/intel_sprite.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/intel_sprite.c
> > > b/drivers/gpu/drm/i915/intel_sprite.c
> > > index 4990d6e84ddf..83880e3a5f3d 100644
> > > --- a/drivers/gpu/drm/i915/intel_sprite.c
> > > +++ b/drivers/gpu/drm/i915/intel_sprite.c
> > > @@ -118,7 +118,7 @@ void intel_pipe_update_start(const struct
> > > intel_crtc_state *new_crtc_state)
> > >  	 * VBL interrupts will start the PSR exit and prevent a
> > > PSR
> > >  	 * re-entry as well.
> > >  	 */
> > > -	if (CAN_PSR(dev_priv) &&
> > > intel_psr_wait_for_idle(dev_priv))
> > > +	if (new_crtc_state->has_psr &&
> > > intel_psr_wait_for_idle(dev_priv))
> > >  		DRM_ERROR("PSR idle timed out, atomic update may
> > > fail\n");
> > >  
> > >  	local_irq_disable();
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