question about potential dead code in vce_v2_0_enable_mgcg()

-----Original Message-----
From: Gustavo A. R. Silva [mailto:[email protected]]
Sent: Wednesday, June 28, 2017 10:22 AM
To: Deucher, Alexander; Koenig, Christian; David Airlie
Cc: [email protected]; [email protected]; linux- [email protected]
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.

Quoted 38 lines

-----Original Message-----
From: Gustavo A. R. Silva [mailto:[email protected]]
Sent: Wednesday, June 28, 2017 10:22 AM
To: Deucher, Alexander; Koenig, Christian; David Airlie
Cc: [email protected]; [email protected]; linux- [email protected]
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.

Quoted 6 lines

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.

Hi Alex,

Quoting "Deucher, Alexander" <[email protected]>:

Quoted 47 lines

Quoted 45 lines

-----Original Message-----
From: Gustavo A. R. Silva [mailto:[email protected]]
Sent: Wednesday, June 28, 2017 10:22 AM
To: Deucher, Alexander; Koenig, Christian; David Airlie
Cc: [email protected]; [email protected]; linux-
[email protected]
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.

Quoted 3 lines

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?

drivers/gpu/drm/radeon/vce_v2_0.c +4 -0

@@ -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

_______________________________________________
amd-gfx mailing list
[email protected]
https://lists.freedesktop.org/mailman/listinfo/amd-gfx

Add function header comment to make it clear that local variable sw_cg is used for debugging and it should not be removed.

Addresses-Coverity-ID: 1198635

Cc Alex Deucher <[email protected]>

Signed-off-by Gustavo A. R. Silva <[email protected]>

---
 drivers/gpu/drm/radeon/vce_v2_0.c | 4 ++++
 1 file changed, 4 insertions(+)

drivers/gpu/drm/radeon/vce_v2_0.c +4 -1

index fce2144..b0a43b6 100644
@@ -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;
--

2.5.0

Quoted 6 lines · Gustavo A. R. Silva

Add function header comment to make it clear that local variable sw_cg is used for debugging and it should not be removed.

Addresses-Coverity-ID: 1198635

Cc Alex Deucher <[email protected]>

Signed-off-by Gustavo A. R. Silva <[email protected]>

Applied. thanks!