On Tue, Nov 28, 2023 at 7:26 PM Benjamin Gaignard <benjamin.gaignard@xxxxxxxxxxxxx> wrote: > > > 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. That sounds weird. Why would a driver that doesn't have a DMA engine need to obtain a scatterlist or the DMA address of the buffer? > 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. Yeah, there probably wouldn't be a way that would give one a 100% certainty, although I'd still insist that the two functions I mentioned should be close to that. Of course a driver can use those functions for some queues, while other queues would be pure software queues, e.g. for some metadata - a simple grep is not enough. Is that perhaps the case for the verisilicon driver? Best regards, Tomasz > > 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; > >>>>
