Re: [PATCH 2/2] drm/i915/psr: Remove wait_for_idle() for PSR2

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Wed, Aug 15, 2018 at 06:35:15PM -0700, Dhinakaran Pandiyan wrote:
> On Mon, 2018-08-13 at 18:10 +0000, Pandiyan, Dhinakaran wrote:
> > On Mon, 2018-08-13 at 09:57 -0700, Rodrigo Vivi wrote:
> > > On Thu, Aug 09, 2018 at 05:41:35PM -0700, Dhinakaran Pandiyan
> > > wrote:
> > > > CI runs show PSR2 does not go to IDLE with selective update
> > > > enabled
> > > > on
> > > > all PSR exit triggers. Specifically, logs indicate the hardware
> > > > enters
> > > > "SLEEP Selective Update" and not "IDLE Reset state' like the
> > > > kernel
> > > > expects. This check was added for PSR1 but incorrectly extended
> > > > to
> > > > PSR2,
> > > > remove this check for PSR2 as there is a plan to test only PSR1
> > > > on
> > > > PSR2
> > > > panels.
> > > > 
> > > > Also add bspec reference to the comment about idle timeout.
> > > > 
> > > > Cc: Tarun Vyas <tarun.vyas@intel.com>
> > > > Cc: José Roberto de Souza <jose.souza@intel.com>
> > > > Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> > > > Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com
> > > > >
> > > > ---
> > > >  drivers/gpu/drm/i915/intel_psr.c | 39 ++++++++++++--------------
> > > > ------
> > > >  1 file changed, 14 insertions(+), 25 deletions(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/i915/intel_psr.c
> > > > b/drivers/gpu/drm/i915/intel_psr.c
> > > > index 5686ddaa6a72..09be9bfee2be 100644
> > > > --- a/drivers/gpu/drm/i915/intel_psr.c
> > > > +++ b/drivers/gpu/drm/i915/intel_psr.c
> > > > @@ -722,37 +722,26 @@ int intel_psr_wait_for_idle(const struct
> > > > intel_crtc_state *new_crtc_state,
> > > >  {
> > > >  	struct intel_crtc *crtc = to_intel_crtc(new_crtc_state-
> > > > > base.crtc);
> > > > 
> > > >  	struct drm_i915_private *dev_priv = to_i915(crtc-
> > > > > base.dev);
> > > > 
> > > > -	i915_reg_t reg;
> > > > -	u32 mask;
> > > > -
> > > > -	if (!new_crtc_state->has_psr)
> > > > -		return 0;
> > > >  
> > > >  	/*
> > > > -	 * The sole user right now is intel_pipe_update_start(),
> > > > -	 * which won't race with psr_enable/disable, which is
> > > > -	 * where psr2_enabled is written to. So, we don't need
> > > > -	 * to acquire the psr.lock. More importantly, we want
> > > > the
> > > > -	 * latency inside intel_pipe_update_start() to be as low
> > > > -	 * as possible, so no need to acquire psr.lock when it
> > > > is
> > > > -	 * not needed and will induce latencies in the atomic
> > > > -	 * update path.
> > > > +	 * The sole user right now is intel_pipe_update_start(),
> > > > which won't
> > > > +	 * race with psr_enable/disable where psr2_enabled is
> > > > written to. So, we
> > > > +	 * don't need to acquire the psr.lock. More importantly,
> > > > we want the
> > > > +	 * latency inside intel_pipe_update_start() to be as low
> > > > as possible, so
> > > > +	 * no need to acquire psr.lock when it is not needed and
> > > > will induce
> > > > +	 * latencies in the atomic update path.
> > > >  	 */
> > > 
> > > I think we shouldn't change this format here to keep patch
> > > cleaner...
> > > if there is any change here I couldn't see because it is changing
> > > all
> > > lines and if there is no change I think it is better not to touch
> > > because
> > > it removes the focus of the real changes.
> > 
> > Okay.
> > > 
> > > > -	if (dev_priv->psr.psr2_enabled) {
> > > > -		reg = EDP_PSR2_STATUS;
> > > > -		mask = EDP_PSR2_STATUS_STATE_MASK;
> > > > -	} else {
> > > > -		reg = EDP_PSR_STATUS;
> > > > -		mask = EDP_PSR_STATUS_STATE_MASK;
> > > > -	}
> > > > +	if (!new_crtc_state->has_psr || READ_ONCE(dev_priv-
> > > > > psr.psr2_enabled))
> > > 
> > > I now see that we are removing psr2 of the picture, but I don't see
> > > how we are
> > > improving psr2 situation here.
> > > what am I missing?
> > > 
> > 
> > When the patch was written, we did not have sufficient tests to tell
> > us
> > the wait_for_idle condition was wrong for PSR2. It was not known
> > whether the wait was *necessary* for PSR2, think of this as a partial
> > revert. Now that CI has pointed out, (and I checked with a PSR2
> > panel)
> > that the condition is wrong, we should be removing it for PSR2. If
> > you
> > think about it, it does improve PSR2 my removing irrelevant code.
> > 
> I'll submit a new version without the comment diff if you are satisfied
> with the above reasoning.

Please add a "FIXME:" here and we can fix psr2 situation later when we understand
it better...
so we at least unblock PSR for now...

> 
> > 
> > > > +		return 0;
> > > >  
> > > >  	/*
> > > > -	 * Max time for PSR to idle = Inverse of the refresh
> > > > rate
> > > > +
> > > > -	 * 6 ms of exit training time + 1.5 ms of aux channel
> > > > -	 * handshake. 50 msec is defesive enough to cover
> > > > everything.
> > > > +	 * From Bspec Panel Self Refresh (BDW+):
> > > 
> > > This is another case, if we didn't change the format only this line
> > > ^
> > > would be in the patch and it would be cleaner and easier to review
> > > the
> > > changes.
> > > 
> > > but my biggest concern with this patch is how do we check now
> > > wait_psr2 idle
> > > 
> > > > +	 * Max. time for PSR to idle = inverse of the refresh
> > > > rate
> > > > + 6 ms of
> > > > +	 * exit training time + 1.5 ms of aux channel handshake.
> > > > 50 ms is
> > > > +	 * defensive enough to cover everything.
> > > >  	 */
> > > > -
> > > > -	return __intel_wait_for_register(dev_priv, reg, mask,
> > > > +	return __intel_wait_for_register(dev_priv,
> > > > EDP_PSR_STATUS,
> > > > +					 EDP_PSR_STATUS_STATE_MA
> > > > SK
> > > > ,
> > > >  					 EDP_PSR_STATUS_STATE_ID
> > > > LE
> > > > , 2, 50,
> > > >  					 out_value);
> > > >  }
> > > > -- 
> > > > 2.17.1
> > > > 
> > > > _______________________________________________
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> > > > Intel-gfx@lists.freedesktop.org
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> > 
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