On Mon, Sep 7, 2020 at 4:02 PM Marek Szyprowski
<m.szyprowski@xxxxxxxxxxx> wrote:
>
> Hi Tomasz,
>
> On 07.09.2020 15:07, Tomasz Figa wrote:
> > On Fri, Sep 4, 2020 at 3:35 PM Marek Szyprowski
> > <m.szyprowski@xxxxxxxxxxx> wrote:
> >> Use recently introduced common wrappers operating directly on the struct
> >> sg_table objects and scatterlist page iterators to make the code a bit
> >> more compact, robust, easier to follow and copy/paste safe.
> >>
> >> No functional change, because the code already properly did all the
> >> scatterlist related calls.
> >>
> >> Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
> >> Reviewed-by: Robin Murphy <robin.murphy@xxxxxxx>
> >> ---
> >> .../common/videobuf2/videobuf2-dma-contig.c | 34 ++++++++-----------
> >> .../media/common/videobuf2/videobuf2-dma-sg.c | 32 +++++++----------
> >> .../common/videobuf2/videobuf2-vmalloc.c | 12 +++----
> >> 3 files changed, 31 insertions(+), 47 deletions(-)
> >>
> > Thanks for the patch! Please see my comments inline.
> >
> >> diff --git a/drivers/media/common/videobuf2/videobuf2-dma-contig.c b/drivers/media/common/videobuf2/videobuf2-dma-contig.c
> >> index ec3446cc45b8..1b242d844dde 100644
> >> --- a/drivers/media/common/videobuf2/videobuf2-dma-contig.c
> >> +++ b/drivers/media/common/videobuf2/videobuf2-dma-contig.c
> >> @@ -58,10 +58,10 @@ static unsigned long vb2_dc_get_contiguous_size(struct sg_table *sgt)
> >> unsigned int i;
> >> unsigned long size = 0;
> >>
> >> - for_each_sg(sgt->sgl, s, sgt->nents, i) {
> >> + for_each_sgtable_dma_sg(sgt, s, i) {
> >> if (sg_dma_address(s) != expected)
> >> break;
> >> - expected = sg_dma_address(s) + sg_dma_len(s);
> >> + expected += sg_dma_len(s);
> >> size += sg_dma_len(s);
> >> }
> >> return size;
> >> @@ -103,8 +103,7 @@ static void vb2_dc_prepare(void *buf_priv)
> >> if (!sgt)
> >> return;
> >>
> >> - dma_sync_sg_for_device(buf->dev, sgt->sgl, sgt->orig_nents,
> >> - buf->dma_dir);
> >> + dma_sync_sgtable_for_device(buf->dev, sgt, buf->dma_dir);
> >> }
> >>
> >> static void vb2_dc_finish(void *buf_priv)
> >> @@ -115,7 +114,7 @@ static void vb2_dc_finish(void *buf_priv)
> >> if (!sgt)
> >> return;
> >>
> >> - dma_sync_sg_for_cpu(buf->dev, sgt->sgl, sgt->orig_nents, buf->dma_dir);
> >> + dma_sync_sgtable_for_cpu(buf->dev, sgt, buf->dma_dir);
> >> }
> >>
> >> /*********************************************/
> >> @@ -275,8 +274,8 @@ static void vb2_dc_dmabuf_ops_detach(struct dma_buf *dbuf,
> >> * memory locations do not require any explicit cache
> >> * maintenance prior or after being used by the device.
> >> */
> >> - dma_unmap_sg_attrs(db_attach->dev, sgt->sgl, sgt->orig_nents,
> >> - attach->dma_dir, DMA_ATTR_SKIP_CPU_SYNC);
> >> + dma_unmap_sgtable(db_attach->dev, sgt, attach->dma_dir,
> >> + DMA_ATTR_SKIP_CPU_SYNC);
> >> sg_free_table(sgt);
> >> kfree(attach);
> >> db_attach->priv = NULL;
> >> @@ -301,8 +300,8 @@ static struct sg_table *vb2_dc_dmabuf_ops_map(
> >>
> >> /* release any previous cache */
> >> if (attach->dma_dir != DMA_NONE) {
> >> - dma_unmap_sg_attrs(db_attach->dev, sgt->sgl, sgt->orig_nents,
> >> - attach->dma_dir, DMA_ATTR_SKIP_CPU_SYNC);
> >> + dma_unmap_sgtable(db_attach->dev, sgt, attach->dma_dir,
> >> + DMA_ATTR_SKIP_CPU_SYNC);
> >> attach->dma_dir = DMA_NONE;
> >> }
> >>
> >> @@ -310,9 +309,8 @@ static struct sg_table *vb2_dc_dmabuf_ops_map(
> >> * mapping to the client with new direction, no cache sync
> >> * required see comment in vb2_dc_dmabuf_ops_detach()
> >> */
> >> - sgt->nents = dma_map_sg_attrs(db_attach->dev, sgt->sgl, sgt->orig_nents,
> >> - dma_dir, DMA_ATTR_SKIP_CPU_SYNC);
> >> - if (!sgt->nents) {
> >> + if (dma_map_sgtable(db_attach->dev, sgt, dma_dir,
> >> + DMA_ATTR_SKIP_CPU_SYNC)) {
> >> pr_err("failed to map scatterlist\n");
> >> mutex_unlock(lock);
> >> return ERR_PTR(-EIO);
> > As opposed to dma_map_sg_attrs(), dma_map_sgtable() now returns an
> > error code on its own. Is it expected to ignore it and return -EIO?
>
> Those errors are more or less propagated to userspace and -EIO has been
> already widely documented in V4L2 documentation as the error code for
> the most of the V4L2 ioctls. I don't want to change it. A possible
> -EINVAL returned from dma_map_sgtable() was just one of the 'generic'
> error codes, not very descriptive in that case. Probably the main
> problem here is that dma_map_sg() and friend doesn't return any error
> codes...
True for the alloc/get_*() callbacks, but the dmabuf_ops_map() ones
are used for the in-kernel DMA-buf exporter ops, called by DMA-buf
importers.
As a side note, returning user-facing error codes from deep internals
of vb2 and having the userspace rely on particular values sounds quite
fragile. For example, I see vb2_dc_attach_dmabuf() returning a return
value coming from dma_buf_attach() directly and __prepare_dmabuf()
propagating it back to __buf_prepare(), which can just return that
back to the userspace. I guess we might have to do some follow-up work
to clean it up.
Best regards,
Tomasz
