Re: [PATCH] media: vimc: Add support for contiguous DMA buffers

[Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>]

Hi Laurent, Dafna,

On Fri, 30 Jul 2021 at 09:35, Dafna Hirschfeld
<dafna.hirschfeld@collabora.com> wrote:
>
> Hi
>
> On 30.07.21 02:19, Laurent Pinchart wrote:
> > The vimc driver is used for testing purpose, and some test use cases
> > involve sharing buffers with a consumer device. Consumers often require
> > DMA contiguous memory, which vimc doesn't currently support. This leads
> > in the best case to usage of bounce buffers, which is very slow, and in
> > the worst case in a complete failure.
> >
> > Add support for the dma-contig allocator in vimc to support those use
> > cases properly. The allocator is selected through a new "allocator"
> > module parameter, which defaults to vmalloc.
> >
> > Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
> > ---
> >   drivers/media/test-drivers/vimc/vimc-capture.c |  9 +++++++--
> >   drivers/media/test-drivers/vimc/vimc-common.h  |  2 ++
> >   drivers/media/test-drivers/vimc/vimc-core.c    | 10 ++++++++++
> >   3 files changed, 19 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/media/test-drivers/vimc/vimc-capture.c b/drivers/media/test-drivers/vimc/vimc-capture.c
> > index 5e9fd902cd37..92b69a6529fb 100644
> > --- a/drivers/media/test-drivers/vimc/vimc-capture.c
> > +++ b/drivers/media/test-drivers/vimc/vimc-capture.c
> > @@ -7,6 +7,7 @@
> >
> >   #include <media/v4l2-ioctl.h>
> >   #include <media/videobuf2-core.h>
> > +#include <media/videobuf2-dma-contig.h>
> >   #include <media/videobuf2-vmalloc.h>
> >
> >   #include "vimc-common.h"
> > @@ -423,14 +424,18 @@ static struct vimc_ent_device *vimc_cap_add(struct vimc_device *vimc,
> >       /* Initialize the vb2 queue */
> >       q = &vcap->queue;
> >       q->type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
> > -     q->io_modes = VB2_MMAP | VB2_DMABUF | VB2_USERPTR;
> > +     q->io_modes = VB2_MMAP | VB2_DMABUF;
>
> maybe to be on the safe side VB2_DMABUF should be set only if vimc_allocator==1 ?
>
> > +     if (vimc_allocator != 1)
>
> maybe define a macro instead of `1` ?
>

This is maybe an overkill, but you can make the parameter accept strings
instead of integers, which makes it "modprobe vimc allocator=vmalloc",
and improves a bit user-friendlyness.

See drivers/media/pci/tw686x/tw686x-core.c.

For a test driver, it is worth the trouble, maybe?

Thanks,
Ezequiel