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

[Christian König]

Am 31.08.21 um 05:44 schrieb guangming.cao@xxxxxxxxxxxx:
> From: Guangming Cao <Guangming.Cao@xxxxxxxxxxxx>
>
> > Am 30.08.21 um 12:01 schrieb guangming.cao@xxxxxxxxxxxx:
> > > From: Guangming Cao <Guangming.Cao@xxxxxxxxxxxx>
> > >
> > > 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?

Yes, that's correct and all of those needs to be synced as far as I know.

See the dma_sync_sgtable_for_cpu() is intentionally for each SG table 
given out.

> > > 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?

That might be the case, nevertheless this change here is illegal from 
the DMA API point of view as far as I can see.

Regards,
Christian.

> > > Signed-off-by: Guangming Cao <Guangming.Cao@xxxxxxxxxxxx>
> > > ---
> > >    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);
> > >