Re: [gpu-drm-radeon] question about potential dead code in vce_v2_0_enable_mgcg()

[Gustavo A. R. Silva]

Hi Alex,

Quoting "Deucher, Alexander" <Alexander.Deucher@xxxxxxx>:

> > -----Original Message-----
> > From: Gustavo A. R. Silva [mailto:garsilva@xxxxxxxxxxxxxx]
> > Sent: Wednesday, June 28, 2017 10:22 AM
> > To: Deucher, Alexander; Koenig, Christian; David Airlie
> > Cc: amd-gfx@xxxxxxxxxxxxxxxxxxxxx; dri-devel@xxxxxxxxxxxxxxxxxxxxx; linux-
> > kernel@xxxxxxxxxxxxxxx
> > Subject: [gpu-drm-radeon] question about potential dead code in
> > vce_v2_0_enable_mgcg()
> >
> >
> > Hello everybody,
> >
> > While looking into Coverity ID 1198635 I ran into the following piece
> > of code at drivers/gpu/drm/radeon/vce_v2_0.c:107:
> >
> > 107void vce_v2_0_enable_mgcg(struct radeon_device *rdev, bool enable)
> > 108{
> > 109        bool sw_cg = false;
> > 110
> > 111        if (enable && (rdev->cg_flags &
> > RADEON_CG_SUPPORT_VCE_MGCG)) {
> > 112                if (sw_cg)
> > 113                        vce_v2_0_set_sw_cg(rdev, true);
> > 114                else
> > 115                        vce_v2_0_set_dyn_cg(rdev, true);
> > 116        } else {
> > 117                vce_v2_0_disable_cg(rdev);
> > 118
> > 119                if (sw_cg)
> > 120                        vce_v2_0_set_sw_cg(rdev, false);
> > 121                else
> > 122                        vce_v2_0_set_dyn_cg(rdev, false);
> > 123        }
> > 124}
> >
> > The issue here is that local variable sw_cg is never updated again
> > after its initialization; which cause some code to be logically dead.
> >
> > My question here is if such variable is there for testing purposes or
> > if it is a sort of an old code leftover that should be removed?
> >
> > In any case I can send a patch to add a comment or remove the dead code.
> >
> > I'd really appreciate any comments on this.
>
> I wanted to leave the code in for debugging if we ran into problems  
> with dynamic clockgating.

Do you mind if I send a patch to add such comment and make it clear  
the purpose of that variable?

--- a/drivers/gpu/drm/radeon/vce_v2_0.c
+++ b/drivers/gpu/drm/radeon/vce_v2_0.c
@@ -104,6 +104,10 @@ static void vce_v2_0_disable_cg(struct  
radeon_device *rdev)
        WREG32(VCE_CGTT_CLK_OVERRIDE, 7);
 }

+/*
+ * Local variable sw_cg is used for debugging purposes, in case we
+ * ran into problems with dynamic clock gating. Don't remove it.
+ */
 void vce_v2_0_enable_mgcg(struct radeon_device *rdev, bool enable)
 {
        bool sw_cg = false;


Thanks for clarifying!
--
Gustavo A. R. Silva