Re: [PATCH] drm/i915/: Initialise trans_min for skl_compute_transition_wm()

Ville Syrjälä
2017-11-08T20:00:09Z

On Wed, Nov 08, 2017 at 10:39:59AM +0530, Mahesh Kumar wrote:
> Hi,
>
>
> On Tuesday 07 November 2017 11:57 PM, Chris Wilson wrote:
> > clang spots
> >
> > drivers/gpu/drm/i915/intel_pm.c:4655:6: warning: variable 'trans_min' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
> > if (INTEL_GEN(dev_priv) >= 10)
> >
> > but fortunately for us we skip the function unless on a gen10+ device.
> > However, to keep the function generic in case we do want to re-enable it
> > for gen9 again, initialise trans_min to 0.
> >
> > References: ca47667f523e ("drm/i915/gen10: Calculate and enable transition WM")
> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > Cc: Mahesh Kumar <mahesh1.kumar@intel.com>
> > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> > Cc: Jani Nikula <jani.nikula@linux.intel.com>
> > Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> > Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> > drivers/gpu/drm/i915/intel_pm.c | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> > index b75c4cf074ff..40da5001be28 100644
> > --- a/drivers/gpu/drm/i915/intel_pm.c
> > +++ b/drivers/gpu/drm/i915/intel_pm.c
> > @@ -4652,6 +4652,7 @@ static void skl_compute_transition_wm(struct intel_crtc_state *cstate,
> > if (!dev_priv->ipc_enabled)
> > goto exit;
> >
> > + trans_min = 0;
> > if (INTEL_GEN(dev_priv) >= 10)
> > trans_min = 4;
> BSpec WA section tells not to enable transition watermark for any GEN-9
> platforms (that was the assumption with this patch)
> But anyway trans_min value for GEN9 is 14 blocks, IMO adding else case
> with trans_min = 14; will be logical solution to this.

Bspec is telling me that 14 is the correct value for gen10 as well.
Looks like the 4 came back from the future.

--
Ville Syrjälä
Intel OTC