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

Sakari Ailus
2017-04-07T12:37:34Z

Hi Shuah,

On Mon, Mar 27, 2017 at 04:51:40PM -0600, Shuah Khan wrote:
> 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.

I can split this, sure. A non-NULL vec indicates a USERPTR buffer. Before
this patch, non-NULL buf->dma_sgt did the same.

>
> >
> > 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
>

The field existed on bc0195aad0daa2ad5b0d76cce22b167bc3435590, i.e. v4.2-rc2
from which the earlier version of this patch was rebased from.

> 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'm not sure what you're referring to. The condition for sync is changed to
use buf->vec instead, i.e. the functionality is not affected.

--
Kind regards,

Sakari Ailus
e-mail: sakari.ailus@iki.fi XMPP: sailus@retiisi.org.uk