linux-kernel - Re: [PATCH 1/7] drm/amdgpu: remove set but not used variable 'mc_shared_chmap' from 'gfx_v6_0.c' and 'gfx_v7

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Date:   Wed, 13 Nov 2019 08:55:47 -0800
From:   Joe Perches <joe@...ches.com>
To:     yu kuai <yukuai3@...wei.com>, alexander.deucher@....com,
        Felix.Kuehling@....com, christian.koenig@....com,
        David1.Zhou@....com, airlied@...ux.ie, daniel@...ll.ch,
        Rex.Zhu@....com, evan.quan@....com
Cc:     linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        amd-gfx@...ts.freedesktop.org, zhengbin13@...wei.com,
        yi.zhang@...wei.com
Subject: Re: [PATCH 1/7] drm/amdgpu: remove set but not used variable
 'mc_shared_chmap' from 'gfx_v6_0.c' and 'gfx_v7_0.c'

On Wed, 2019-11-13 at 20:44 +0800, yu kuai wrote:
> Fixes gcc '-Wunused-but-set-variable' warning:
> 
> drivers/gpu/drm/amd/amdgpu/gfx_v6_0.c: In function
> ‘gfx_v6_0_constants_init’:
> drivers/gpu/drm/amd/amdgpu/gfx_v6_0.c:1579:6: warning: variable
> ‘mc_shared_chmap’ set but not used [-Wunused-but-set-variable]
[]
> diff --git a/drivers/gpu/drm/amd/amdgpu/gfx_v6_0.c b/drivers/gpu/drm/amd/amdgpu/gfx_v6_0.c
[]
> @@ -1678,7 +1678,6 @@ static void gfx_v6_0_constants_init(struct amdgpu_device *adev)
>  
>  	WREG32(mmBIF_FB_EN, BIF_FB_EN__FB_READ_EN_MASK | BIF_FB_EN__FB_WRITE_EN_MASK);
>  
> -	mc_shared_chmap = RREG32(mmMC_SHARED_CHMAP);

I do not know the hardware but frequently hardware like
this has read ordering requirements and various registers
can not be read in a random order.

Does removing this read have no effect on the hardware?

>  	adev->gfx.config.mc_arb_ramcfg = RREG32(mmMC_ARB_RAMCFG);
>  	mc_arb_ramcfg = adev->gfx.config.mc_arb_ramcfg;
>  
> diff --git a/drivers/gpu/drm/amd/amdgpu/gfx_v7_0.c b/drivers/gpu/drm/amd/amdgpu/gfx_v7_0.c
[]
> @@ -4336,7 +4336,6 @@ static void gfx_v7_0_gpu_early_init(struct amdgpu_device *adev)
>  		break;
>  	}
>  
> -	mc_shared_chmap = RREG32(mmMC_SHARED_CHMAP);
>  	adev->gfx.config.mc_arb_ramcfg = RREG32(mmMC_ARB_RAMCFG);
>  	mc_arb_ramcfg = adev->gfx.config.mc_arb_ramcfg;

Same question.