linux-kernel - Re: [PATCH] dma-buf: heaps: remove duplicated cache sync

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Message-ID: <dd5ba603-8c9d-f6a0-cbcc-dfb353fb6701@amd.com>
Date:   Mon, 30 Aug 2021 12:16:28 +0200
From:   Christian König <christian.koenig@....com>
To:     guangming.cao@...iatek.com, Sumit Semwal <sumit.semwal@...aro.org>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Liam Mark <lmark@...eaurora.org>,
        Laura Abbott <labbott@...hat.com>,
        Brian Starkey <Brian.Starkey@....com>,
        John Stultz <john.stultz@...aro.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        "open list:DMA-BUF HEAPS FRAMEWORK" <linux-media@...r.kernel.org>,
        "open list:DMA-BUF HEAPS FRAMEWORK" <dri-devel@...ts.freedesktop.org>,
        "moderated list:DMA-BUF HEAPS FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>,
        open list <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>
Cc:     wsd_upstream@...iatek.com
Subject: Re: [PATCH] dma-buf: heaps: remove duplicated cache sync

Am 30.08.21 um 12:01 schrieb guangming.cao@...iatek.com:
> From: Guangming Cao <Guangming.Cao@...iatek.com>
>
> Current flow, one dmabuf maybe call cache sync many times if
> it has beed mapped more than one time.

Well I'm not an expert on DMA heaps, but this will most likely not work 
correctly.

> Is there any case that attachments of one dmabuf will points to
> different memory? If not, seems do sync only one time is more better.

I think that this can happen, yes.

Christian.


>
> Signed-off-by: Guangming Cao <Guangming.Cao@...iatek.com>
> ---
>   drivers/dma-buf/heaps/system_heap.c | 14 ++++++++------
>   1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c
> index 23a7e74ef966..909ef652a8c8 100644
> --- a/drivers/dma-buf/heaps/system_heap.c
> +++ b/drivers/dma-buf/heaps/system_heap.c
> @@ -162,9 +162,10 @@ static int system_heap_dma_buf_begin_cpu_access(struct dma_buf *dmabuf,
>   		invalidate_kernel_vmap_range(buffer->vaddr, buffer->len);
>   
>   	list_for_each_entry(a, &buffer->attachments, list) {
> -		if (!a->mapped)
> -			continue;
> -		dma_sync_sgtable_for_cpu(a->dev, a->table, direction);
> +		if (a->mapped) {
> +			dma_sync_sgtable_for_cpu(a->dev, a->table, direction);
> +			break;
> +		}
>   	}
>   	mutex_unlock(&buffer->lock);
>   
> @@ -183,9 +184,10 @@ static int system_heap_dma_buf_end_cpu_access(struct dma_buf *dmabuf,
>   		flush_kernel_vmap_range(buffer->vaddr, buffer->len);
>   
>   	list_for_each_entry(a, &buffer->attachments, list) {
> -		if (!a->mapped)
> -			continue;
> -		dma_sync_sgtable_for_device(a->dev, a->table, direction);
> +		if (!a->mapped) {
> +			dma_sync_sgtable_for_device(a->dev, a->table, direction);
> +			break;
> +		}
>   	}
>   	mutex_unlock(&buffer->lock);
>