Re: [PATCH 07/55] media: imx8-isi: Stop abusing of min_buffers_needed field

[Benjamin Gaignard]

Le 28/11/2023 à 10:35, Tomasz Figa a écrit :
> On Tue, Nov 28, 2023 at 6:31 PM Benjamin Gaignard
> <benjamin.gaignard@xxxxxxxxxxxxx> wrote:
> > Le 27/11/2023 à 18:07, Laurent Pinchart a écrit :
> > > Hi Benjamin,
> > >
> > > Thank you for the patch.
> > >
> > > On Mon, Nov 27, 2023 at 05:54:06PM +0100, Benjamin Gaignard wrote:
> > > > 'min_buffers_needed' is suppose to be used to indicate the number
> > > > of buffers needed by DMA engine to start streaming.
> > > > imx8-isi driver doesn't use DMA engine and just want to specify
> > > What do you mean, "doesn't use DMA engine" ? The ISI surely has DMA
> > > engines :-)
> > I have done assumption on drivers given if they use or dma_* functions.
> I suspect the use of vb2_dma_sg_plane_desc() and
> vb2_dma_contig_plane_dma_addr() may be more correlated to whether
> there is a DMA involved or not. Usually V4L2 drivers don't really have
> to deal with the DMA API explicitly, because the vb2 framework handles
> most of the work.

Unfortunately isn't not true either, for example verisilicon driver use
these function but doesn't need DMA engine.
I haven't found yet a 100% criteria to decide if driver use or not DMA engine
so I plan to fix case by case given maintainers remarks.

Regards,
Benjamin

> Best regards,
> Tomasz
>
> > I have considers that all PCI drivers are using DMA engine and
> > I don't know the design for each drivers so I hope to get this information
> > from maintainers and fix that in v2.
> > If imx8-isi driver needs a minimum number of buffers before start streaming
> > I will do a v2 and use min_dma_buffers_needed instead.
> >
> > Regards,
> > Benjamin
> >
> > > > the minimum number of buffers to allocate when calling VIDIOC_REQBUFS.
> > > > That 'min_reqbufs_allocation' field purpose so use it.
> > > >
> > > > Signed-off-by: Benjamin Gaignard <benjamin.gaignard@xxxxxxxxxxxxx>
> > > > CC: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> > > > CC: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
> > > > CC: Shawn Guo <shawnguo@xxxxxxxxxx>
> > > > CC: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>
> > > > CC: Pengutronix Kernel Team <kernel@xxxxxxxxxxxxxx>
> > > > CC: Fabio Estevam <festevam@xxxxxxxxx>
> > > > CC: NXP Linux Team <linux-imx@xxxxxxx>
> > > > ---
> > > >    drivers/media/platform/nxp/imx8-isi/imx8-isi-video.c | 2 +-
> > > >    1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/media/platform/nxp/imx8-isi/imx8-isi-video.c b/drivers/media/platform/nxp/imx8-isi/imx8-isi-video.c
> > > > index 49bca2b01cc6..81673ff9084b 100644
> > > > --- a/drivers/media/platform/nxp/imx8-isi/imx8-isi-video.c
> > > > +++ b/drivers/media/platform/nxp/imx8-isi/imx8-isi-video.c
> > > > @@ -1453,7 +1453,7 @@ int mxc_isi_video_register(struct mxc_isi_pipe *pipe,
> > > >       q->mem_ops = &vb2_dma_contig_memops;
> > > >       q->buf_struct_size = sizeof(struct mxc_isi_buffer);
> > > >       q->timestamp_flags = V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC;
> > > > -    q->min_buffers_needed = 2;
> > > > +    q->min_reqbufs_allocation = 2;
> > > >       q->lock = &video->lock;
> > > >       q->dev = pipe->isi->dev;