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 12:52 -0700, Tarun Vyas wrote:
> On Mon, Jul 09, 2018 at 11:58:52AM -0700, Dhinakaran Pandiyan wrote:
> > 
> > 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.

I looked at the code and spec again, PSR isn't tied to "pipe A" The
driver allows PSR only on "port A" + "transcoder eDP", but the pipe
itself can be any one of the possible options.

> > > > > 
> > > > > 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;
> > 	...
> > }
> Hmm, but the CAN_PSR check is already taken care of by
> intel_psr_compute_config() which then sets has_psr, so just
> 	if (!crtc_state->has_psr)
> 		return;
> should suffice, right ?
> 
Yeah, we can assume at this point state->has_psr is set correctly.

> But then, we incur a function call for non-PSR pipes, which will
> return right away.

That should be okay, having the PSR related check inside the function
looks cleaner IMO. 

> > 
> > 
> > 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();
> > > _______________________________________________
> > > Intel-gfx mailing list
> > > Intel-gfx@lists.freedesktop.org
> > > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
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