Re: [PATCH 11/14] drm/i915: Fix latency==0 handling for level 0 watermark on skl+

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Thu, Nov 08, 2018 at 04:01:18PM -0800, Matt Roper wrote:
> On Thu, Nov 01, 2018 at 05:06:02PM +0200, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > If the level 0 latency is 0 we can't do anything. Return an error
> > rather than success.
> > 
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> Is it possible to get 0 latency here?  I thought we increased the
> latency to 2us if punit told us that level0=0 (WaWmMemoryReadLatency)?

Yeah, under normal circumstances this shouldn't happen. But you
can zero out the level 0 latency via debugfs. Should probably note
that in the commit message.

> 
> 
> Matt
> 
> > ---
> >  drivers/gpu/drm/i915/intel_pm.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> > index 6fa1634e2db5..bd5f16bc7e08 100644
> > --- a/drivers/gpu/drm/i915/intel_pm.c
> > +++ b/drivers/gpu/drm/i915/intel_pm.c
> > @@ -4703,8 +4703,10 @@ static int skl_compute_plane_wm(const struct drm_i915_private *dev_priv,
> >  	bool apply_memory_bw_wa = skl_needs_memory_bw_wa(state);
> >  	uint32_t min_disp_buf_needed;
> >  
> > -	if (latency == 0 ||
> > -	    !intel_wm_plane_visible(cstate, intel_pstate)) {
> > +	if (latency == 0)
> > +		return level == 0 ? -EINVAL : 0;
> > +
> > +	if (!intel_wm_plane_visible(cstate, intel_pstate)) {
> >  		result->plane_en = false;
> >  		return 0;
> >  	}
> > -- 
> > 2.18.1
> > 
> > _______________________________________________
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> > Intel-gfx@lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 
> -- 
> Matt Roper
> Graphics Software Engineer
> IoTG Platform Enabling & Development
> Intel Corporation
> (916) 356-2795

-- 
Ville Syrjälä
Intel
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