Re: [RFC v2 07/11] vb2: dma-contig: Remove redundant sgt_base field

Shuah Khan
2017-03-27T22:51:42Z

On Thu, Dec 15, 2016 at 6:24 PM, Laurent Pinchart
<laurent.pinchart+renesas@ideasonboard.com> wrote:
> From: Sakari Ailus <sakari.ailus@linux.intel.com>
>
> The struct vb2_dc_buf contains two struct sg_table fields: sgt_base and
> dma_sgt. The former is used by DMA-BUF buffers whereas the latter is used
> by USERPTR.
>
> Unify the two, leaving dma_sgt.

I think this patch should be split in two.

1. Unifying dma_sgt and sgt_base

>
> MMAP buffers do not need cache flushing since they have been allocated
> using dma_alloc_coherent().

2. That uses vec to check for checking for no flush needed condition.

>
> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> ---
> Changes since v1:
>
> - Test for MMAP or DMABUF type through the vec field instead of the now
> gone vma field.

What is this gone vma field? Did I miss a patch in the series that
makes this change? This check that is changed used dma_sgt and
db_attach vma

These comments don't agree with the code change.

> - Move the vec field to a USERPTR section in struct vb2_dc_buf, where
> the vma field was located.
> ---
> drivers/media/v4l2-core/videobuf2-dma-contig.c | 25 +++++++++++++------------
> 1 file changed, 13 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/media/v4l2-core/videobuf2-dma-contig.c b/drivers/media/v4l2-core/videobuf2-dma-contig.c
> index fb6a177be461..2a00d12ffee2 100644
> --- a/drivers/media/v4l2-core/videobuf2-dma-contig.c
> +++ b/drivers/media/v4l2-core/videobuf2-dma-contig.c
> @@ -30,12 +30,13 @@ struct vb2_dc_buf {
> unsigned long attrs;
> enum dma_data_direction dma_dir;
> struct sg_table *dma_sgt;
> - struct frame_vector *vec;
>
> /* MMAP related */
> struct vb2_vmarea_handler handler;
> atomic_t refcount;
> - struct sg_table *sgt_base;
> +
> + /* USERPTR related */
> + struct frame_vector *vec;
>
> /* DMABUF related */
> struct dma_buf_attachment *db_attach;
> @@ -95,7 +96,7 @@ static void vb2_dc_prepare(void *buf_priv)
> struct sg_table *sgt = buf->dma_sgt;
>
> /* DMABUF exporter will flush the cache for us */
> - if (!sgt || buf->db_attach)
> + if (!buf->vec)
> return;

With the unification dma_sgt is valid for MMAP buffers after vb2_dma_sg_alloc()
if dma_sgt is not null, sync happens - the patch description doesn't seem to be
in sync with the change.

I might be missing something. I think it would help if these two changes are
split since they are really separate changes.

thanks,
-- Shuah

>
> dma_sync_sg_for_device(buf->dev, sgt->sgl, sgt->orig_nents,
> @@ -108,7 +109,7 @@ static void vb2_dc_finish(void *buf_priv)
> struct sg_table *sgt = buf->dma_sgt;
>
> /* DMABUF exporter will flush the cache for us */
> - if (!sgt || buf->db_attach)
> + if (!buf->vec)
> return;
>
> dma_sync_sg_for_cpu(buf->dev, sgt->sgl, sgt->orig_nents, buf->dma_dir);
> @@ -125,9 +126,9 @@ static void vb2_dc_put(void *buf_priv)
> if (!atomic_dec_and_test(&buf->refcount))
> return;
>
> - if (buf->sgt_base) {
> - sg_free_table(buf->sgt_base);
> - kfree(buf->sgt_base);
> + if (buf->dma_sgt) {
> + sg_free_table(buf->dma_sgt);
> + kfree(buf->dma_sgt);
> }
> dma_free_attrs(buf->dev, buf->size, buf->cookie, buf->dma_addr,
> buf->attrs);
> @@ -239,13 +240,13 @@ static int vb2_dc_dmabuf_ops_attach(struct dma_buf *dbuf, struct device *dev,
> /* Copy the buf->base_sgt scatter list to the attachment, as we can't
> * map the same scatter list to multiple attachments at the same time.
> */
> - ret = sg_alloc_table(sgt, buf->sgt_base->orig_nents, GFP_KERNEL);
> + ret = sg_alloc_table(sgt, buf->dma_sgt->orig_nents, GFP_KERNEL);
> if (ret) {
> kfree(attach);
> return -ENOMEM;
> }
>
> - rd = buf->sgt_base->sgl;
> + rd = buf->dma_sgt->sgl;
> wr = sgt->sgl;
> for (i = 0; i < sgt->orig_nents; ++i) {
> sg_set_page(wr, sg_page(rd), rd->length, rd->offset);
> @@ -396,10 +397,10 @@ static struct dma_buf *vb2_dc_get_dmabuf(void *buf_priv, unsigned long flags)
> exp_info.flags = flags;
> exp_info.priv = buf;
>
> - if (!buf->sgt_base)
> - buf->sgt_base = vb2_dc_get_base_sgt(buf);
> + if (!buf->dma_sgt)
> + buf->dma_sgt = vb2_dc_get_base_sgt(buf);
>
> - if (WARN_ON(!buf->sgt_base))
> + if (WARN_ON(!buf->dma_sgt))
> return NULL;
>
> dbuf = dma_buf_export(&exp_info);
> --
> Regards,
>
> Laurent Pinchart
>
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