On Wed, Nov 29, 2023 at 05:39:25PM +0900, Tomasz Figa wrote: > On Wed, Nov 29, 2023 at 5:28 PM Benjamin Gaignard wrote: > > Le 29/11/2023 à 05:17, Tomasz Figa a écrit : > > > On Tue, Nov 28, 2023 at 7:26 PM Benjamin Gaignard wrote: > > >> Le 28/11/2023 à 10:35, Tomasz Figa a écrit : > > >>> On Tue, Nov 28, 2023 at 6:31 PM Benjamin Gaignard wrote: > > >>>> Le 27/11/2023 à 18:07, Laurent Pinchart a écrit : > > >>>>> 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? > > > > Just because the hardware needs the physical address of the buffer to access it. > > Right, and the part of the hardware that accesses the memory is called > a 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. > > > > > > 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? > > > > Verisilicon hardware block doesn't have IOMMU so it needs the physical > > addresses of all the buffers it use (input buffer, reference frame buffers, etc...). > > No DMA engine involved here it is just how the hardware is working. > > I think we need to clarify what you mean by DMA engine. If it's > basically a standalone hardware block that does the DMA for another > hardware block, i.e. such as the standalone DMA engines under > drivers/dma, then I'd like to ask what the relation is between using > an external DMA engine and min_buffers_needed. Yes, there seems to have been some confusion, DMA engine != dmaengine.h. > > Expect functions like dma_release_channel() or being in PCI directory, > > I don't have found any magical way to know if a driver needs a minimum number of buffers before start streaming. > > I can only read the code and do assumptions for the other cases. > > I hope maintainers, like Laurent or you, will answer to this question for each driver. > > In theory that could work too, so hopefully we can achieve that. Some > drivers may not have very active maintainers... And other maintainers > who never worked with such drivers are as suited to read the code and > guess the expected state as you. That said, let's make sure that > everyone involved does their best, without pushing the task around. We can rely on individual drivers maintainers for review, but the initial work needs to make a reasonable effort to analyze the drivers and find the right value for min_buffers_needed and min_reqbufs_allocation. > > >>>> 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. > > >>>> > > >>>>>> 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; > > >>>>>> -- Regards, Laurent Pinchart
