Re: [PATCH v9 12/16] drm/panfrost: Skip cache flush/invalidate when enabling perfcnt

[Boris Brezillon]

On Sat, 12 Sep 2026 00:28:13 +0100
Adrián Larumbe <adrian.larumbe@xxxxxxxxxxxxx> wrote:

> The GPU cache flush/invalidate operation is unnecessary. First off, the
> GPU doesn't read off the perfcnt sample buffer, only writes into it, so
> an invalidate doesn't make a difference. Then flushing GPU caches after
> each sample has been written is enough for the CPU to see updated values.
> 
> Signed-off-by: Adrián Larumbe <adrian.larumbe@xxxxxxxxxxxxx>

Reviewed-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx>

> ---
>  drivers/gpu/drm/panfrost/panfrost_perfcnt.c | 15 ++-------------
>  1 file changed, 2 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_perfcnt.c b/drivers/gpu/drm/panfrost/panfrost_perfcnt.c
> index f71534e741b6..ffc77121070e 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_perfcnt.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_perfcnt.c
> @@ -124,21 +124,10 @@ static int panfrost_perfcnt_enable_locked(struct panfrost_device *pfdev,
>  	panfrost_gem_internal_set_label(&bo->base, "Perfcnt sample buffer");
>  
>  	/*
> -	 * Invalidate the cache and clear the counters to start from a fresh
> -	 * state.
> +	 * Clear the counters to start from a fresh state.
>  	 */
> -	reinit_completion(&pfdev->perfcnt->dump_comp);
> -	gpu_write(pfdev, GPU_INT_CLEAR,
> -		  GPU_IRQ_CLEAN_CACHES_COMPLETED |
> -		  GPU_IRQ_PERFCNT_SAMPLE_COMPLETED);
> +	gpu_write(pfdev, GPU_INT_CLEAR, GPU_IRQ_PERFCNT_SAMPLE_COMPLETED);
>  	gpu_write(pfdev, GPU_CMD, GPU_CMD_PERFCNT_CLEAR);
> -	gpu_write(pfdev, GPU_CMD, GPU_CMD_CLEAN_INV_CACHES);
> -	ret = wait_for_completion_timeout(&pfdev->perfcnt->dump_comp,
> -					  msecs_to_jiffies(1000));
> -	if (!ret) {
> -		ret = -ETIMEDOUT;
> -		goto err_vunmap;
> -	}
>  
>  	ret = panfrost_mmu_as_get(pfdev, perfcnt->mapping->mmu);
>  	if (ret < 0)
>