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

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Ezequiel,

On Fri, Jul 30, 2021 at 01:13:20PM -0300, Ezequiel Garcia wrote:
> On Fri, 30 Jul 2021 at 09:35, Dafna Hirschfeld wrote:
> > 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?

I copied the values from vivid, which uses an array of integers. As vimc
needs a single parameter only, a string could make more sense. I'll
submit a v3 with a string if there's a consensus for that.

-- 
Regards,

Laurent Pinchart