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

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Message-ID: <CADnq5_NhSDyBRSTpYEnBnSNG1AC=W_bHew-VcU1MxzaBcAURnQ@mail.gmail.com>
Date:   Thu, 29 Jun 2017 08:34:53 -0400
From:   Alex Deucher <alexdeucher@...il.com>
To:     "Gustavo A. R. Silva" <garsilva@...eddedor.com>
Cc:     "Deucher, Alexander" <Alexander.Deucher@....com>,
        David Airlie <airlied@...ux.ie>,
        Maling list - DRI developers 
        <dri-devel@...ts.freedesktop.org>,
        "Koenig, Christian" <Christian.Koenig@....com>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [gpu-drm-radeon] question about potential dead code in vce_v2_0_enable_mgcg()

On Wed, Jun 28, 2017 at 7:08 PM, Gustavo A. R. Silva
<garsilva@...eddedor.com> wrote:
> Hi Alex,
>
> Quoting "Deucher, Alexander" <Alexander.Deucher@....com>:
>
>>> -----Original Message-----
>>> From: Gustavo A. R. Silva [mailto:garsilva@...eddedor.com]
>>> Sent: Wednesday, June 28, 2017 10:22 AM
>>> To: Deucher, Alexander; Koenig, Christian; David Airlie
>>> Cc: amd-gfx@...ts.freedesktop.org; dri-devel@...ts.freedesktop.org;
>>> linux-
>>> kernel@...r.kernel.org
>>> 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?

Sure.  Thanks.

Alex

>
> --- 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
>
>
>
>
>
>
> _______________________________________________
> amd-gfx mailing list
> amd-gfx@...ts.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/amd-gfx

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