linux-kernel - Re: [PATCH 2/2] drm/msm: Don't overwrite hw fence in hw

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Date:   Wed, 15 Jun 2022 13:03:24 -0500
From:   Steev Klimaszewski <steev@...i.org>
To:     Rob Clark <robdclark@...il.com>, dri-devel@...ts.freedesktop.org
Cc:     freedreno@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        Rob Clark <robdclark@...omium.org>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Akhil P Oommen <quic_akhilpo@...cinc.com>,
        Jonathan Marek <jonathan@...ek.ca>,
        Christian König <christian.koenig@....com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] drm/msm: Don't overwrite hw fence in hw_init


On 6/15/22 10:01 AM, Rob Clark wrote:
> From: Rob Clark <robdclark@...omium.org>
>
> Prior to the last commit, this could result in setting the GPU
> written fence value back to an older value, if we had missed
> updating completed_fence prior to suspend.  This was mostly
> harmless as the GPU would eventually overwrite it again with
> the correct value.  But we should just not do this.  Instead
> just leave a sanity check that the fence looks plausible (in
> case the GPU scribbled on memory).
>
> Reported-by: Steev Klimaszewski <steev@...i.org>
> Fixes: 95d1deb02a9c ("drm/msm/gem: Add fenced vma unpin")
> Signed-off-by: Rob Clark <robdclark@...omium.org>
> ---
>   drivers/gpu/drm/msm/adreno/adreno_gpu.c | 11 ++++++++---
>   drivers/gpu/drm/msm/msm_gpu.c           |  2 +-
>   2 files changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/adreno/adreno_gpu.c b/drivers/gpu/drm/msm/adreno/adreno_gpu.c
> index e1aef4875e2f..dd044d557c7c 100644
> --- a/drivers/gpu/drm/msm/adreno/adreno_gpu.c
> +++ b/drivers/gpu/drm/msm/adreno/adreno_gpu.c
> @@ -498,10 +498,15 @@ int adreno_hw_init(struct msm_gpu *gpu)
>   
>   		ring->cur = ring->start;
>   		ring->next = ring->start;
> -
> -		/* reset completed fence seqno: */
> -		ring->memptrs->fence = ring->fctx->completed_fence;
>   		ring->memptrs->rptr = 0;
> +
> +		/* Detect and clean up an impossible fence, ie. if GPU managed
> +		 * to scribble something invalid, we don't want that to confuse
> +		 * us into mistakingly believing that submits have completed.
> +		 */
> +		if (fence_before(ring->fctx->last_fence, ring->memptrs->fence)) {
> +			ring->memptrs->fence = ring->fctx->last_fence;
> +		}
>   	}
>   
>   	return 0;
> diff --git a/drivers/gpu/drm/msm/msm_gpu.c b/drivers/gpu/drm/msm/msm_gpu.c
> index b61078f0cd0f..8c00f9187c03 100644
> --- a/drivers/gpu/drm/msm/msm_gpu.c
> +++ b/drivers/gpu/drm/msm/msm_gpu.c
> @@ -430,7 +430,7 @@ static void recover_worker(struct kthread_work *work)
>   		 * one more to clear the faulting submit
>   		 */
>   		if (ring == cur_ring)
> -			fence++;
> +			ring->memptrs->fence = ++fence;
>   
>   		msm_update_fence(ring->fctx, fence);
>   	}

Tested on the Lenovo Yoga C630

Tested-by: Steev Klimaszewski <steev@...i.org>