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

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Date:   Tue, 31 Aug 2021 11:44:05 +0800
From:   <guangming.cao@...iatek.com>
To:     <christian.koenig@....com>
CC:     <Brian.Starkey@....com>, <benjamin.gaignard@...aro.org>,
        <dri-devel@...ts.freedesktop.org>, <guangming.cao@...iatek.com>,
        <john.stultz@...aro.org>, <labbott@...hat.com>,
        <linaro-mm-sig@...ts.linaro.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-media@...r.kernel.org>,
        <linux-mediatek@...ts.infradead.org>, <lmark@...eaurora.org>,
        <matthias.bgg@...il.com>, <sumit.semwal@...aro.org>,
        <wsd_upstream@...iatek.com>,
        Guangming Cao <Guangming.Cao@...iatek.com>
Subject: Re: [PATCH] dma-buf: heaps: remove duplicated cache sync

From: Guangming Cao <Guangming.Cao@...iatek.com>

> 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.
>
All attachments of one dmabuf will add into a list, I think it means dmabuf
supports map more than one time. Could you tell me more about it?

> > 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.
>
Seems it's a very special case on Android, if you don't mind, could you
tell me more about it?

>
> >
> > 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);
> >