[PATCH v1 1/8] drm/amdgpu: read back register after written

[Wu, David]

hmm... I knew that - but I would rather add that in case 
jpeg_v1_0_start() might change.
A little conservative ...

Thanks,
David
On 5/14/2025 1:33 PM, Dong, Ruijing wrote:
> [AMD Official Use Only - AMD Internal Distribution Only]
>
> This patch is not needed as it has the read-back in jpeg_v1_0_start();
>
> Thanks,
> Ruijing
>
> -----Original Message-----
> From: Wu, David<David.Wu3 at amd.com>
> Sent: Wednesday, May 14, 2025 1:23 PM
> To:amd-gfx at lists.freedesktop.org; Deucher, Alexander<Alexander.Deucher at amd.com>
> Cc: Koenig, Christian<Christian.Koenig at amd.com>; Liu, Leo<Leo.Liu at amd.com>; Jiang, Sonny<Sonny.Jiang at amd.com>; Dong, Ruijing<Ruijing.Dong at amd.com>
> Subject: [PATCH v1 1/8] drm/amdgpu: read back register after written
>
> The addition of register read-back in VCN v1.0 is intended to prevent potential race conditions.
>
> Signed-off-by: David (Ming Qiang) Wu<David.Wu3 at amd.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/vcn_v1_0.c | 10 ++++++++++
>   1 file changed, 10 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/vcn_v1_0.c b/drivers/gpu/drm/amd/amdgpu/vcn_v1_0.c
> index 21b57c29bf7d..f56b623713c9 100644
> --- a/drivers/gpu/drm/amd/amdgpu/vcn_v1_0.c
> +++ b/drivers/gpu/drm/amd/amdgpu/vcn_v1_0.c
> @@ -1009,6 +1009,11 @@ static int vcn_v1_0_start_spg_mode(struct amdgpu_vcn_inst *vinst)
>
>          jpeg_v1_0_start(adev, 0);
>
> +       /* Keeping one read-back to ensure all register writes are done, otherwise
> +        * it may introduce race conditions
> +        */
> +       RREG32_SOC15(UVD, 0, mmUVD_RBC_RB_WPTR);
> +
>          return 0;
>   }
>
> @@ -1154,6 +1159,11 @@ static int vcn_v1_0_start_dpg_mode(struct amdgpu_vcn_inst *vinst)
>
>          jpeg_v1_0_start(adev, 1);
>
> +       /* Keeping one read-back to ensure all register writes are done, otherwise
> +        * it may introduce race conditions
> +        */
> +       RREG32_SOC15(UVD, 0, mmUVD_RBC_RB_WPTR);
> +
>          return 0;
>   }
>
> --
> 2.49.0
>
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