Hi Tomasz,
and thanks for your review!
On 2025-01-27 at 20:18 +09, Tomasz Figa <tfiga@xxxxxxxxxxxx> wrote:
> Hi Mikhail,
>
> On Thu, Jan 16, 2025 at 2:25 AM Mikhail Rudenko <mike.rudenko@xxxxxxxxx> wrote:
>>
>> When support for V4L2_FLAG_MEMORY_NON_CONSISTENT was removed in
>> commit 129134e5415d ("media: media/v4l2: remove
>> V4L2_FLAG_MEMORY_NON_CONSISTENT flag"),
>> vb2_dc_dmabuf_ops_{begin,end}_cpu_access() functions were made
>> no-ops. Later, when support for V4L2_MEMORY_FLAG_NON_COHERENT was
>> introduced in commit c0acf9cfeee0 ("media: videobuf2: handle
>> V4L2_MEMORY_FLAG_NON_COHERENT flag"), the above functions remained
>> no-ops, making cache maintenance for non-coherent dmabufs allocated by
>> dma-contig impossible.
>>
>> Fix this by reintroducing dma_sync_sg_for_{cpu,device} calls to
>> vb2_dc_dmabuf_ops_{begin,end}_cpu_access() functions for non-coherent
>> buffers.
>>
>> Fixes: c0acf9cfeee0 ("media: videobuf2: handle V4L2_MEMORY_FLAG_NON_COHERENT flag")
>> Cc: stable@xxxxxxxxxxxxxxx
>> Signed-off-by: Mikhail Rudenko <mike.rudenko@xxxxxxxxx>
>> ---
>> drivers/media/common/videobuf2/videobuf2-dma-contig.c | 14 ++++++++++++++
>> 1 file changed, 14 insertions(+)
>>
>
> Thanks a lot for the patch!
> Sorry, for the delay. Ended up being sick with some nasty cold that
> took quite a while to recover.
> Please take a look at my comments inline.
>
>> diff --git a/drivers/media/common/videobuf2/videobuf2-dma-contig.c b/drivers/media/common/videobuf2/videobuf2-dma-contig.c
>> index bb0b7fa67b539aa73ad5ccf3c3bc318e26f8a4cb..889d6c11e15ab5cd4b4c317e865f1fef92df4b66 100644
>> --- a/drivers/media/common/videobuf2/videobuf2-dma-contig.c
>> +++ b/drivers/media/common/videobuf2/videobuf2-dma-contig.c
>> @@ -427,6 +427,13 @@ static int
>> vb2_dc_dmabuf_ops_begin_cpu_access(struct dma_buf *dbuf,
>> enum dma_data_direction direction)
>> {
>> + struct vb2_dc_buf *buf = dbuf->priv;
>> + struct sg_table *sgt = buf->dma_sgt;
>> +
>> + if (!buf->non_coherent_mem || buf->vb->skip_cache_sync_on_finish)
>
> skip_cache_sync_on_finish shouldn't apply to this function, because
> the buffer was shared with an external DMA-buf importer and we don't
> know in what state it is at this point.
>
Ack, will fix in v3.
>> + return 0;
>> +
>
> We should also take care of the kernel mapping if it exists, because
> on some platforms it may not be coherent with the userspace one -
> using flush_kernel_vmap_range(). Please check how
> vb2_dc_prepare()/vb2_dc_finish() do it.
>
Thanks for the pointer, will do so in v3.
>> + dma_sync_sg_for_cpu(buf->dev, sgt->sgl, sgt->nents, buf->dma_dir);
>
> We can use the dma_sync_sgtable_*() variant here so we can just pass
> the entire sgt to it.
>
Will do so.
>> return 0;
>> }
>>
>> @@ -434,6 +441,13 @@ static int
>> vb2_dc_dmabuf_ops_end_cpu_access(struct dma_buf *dbuf,
>> enum dma_data_direction direction)
>> {
>> + struct vb2_dc_buf *buf = dbuf->priv;
>> + struct sg_table *sgt = buf->dma_sgt;
>> +
>> + if (!buf->non_coherent_mem || buf->vb->skip_cache_sync_on_prepare)
>> + return 0;
>> +
>> + dma_sync_sg_for_device(buf->dev, sgt->sgl, sgt->nents, buf->dma_dir);
>> return 0;
>
> Overall the same comments here as for
> vb2_dc_dmabuf_ops_begin_cpu_access() +/- flush would change to
> invalidate.
Ack.
> Best regards,
> Tomasz
--
Best regards,
Mikhail Rudenko
