From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b="oqdRt6ow" Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [IPv6:2001:4b98:dc2:55:216:3eff:fef7:d647]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1C6EDC4; Wed, 29 Nov 2023 02:24:29 -0800 (PST) Received: from pendragon.ideasonboard.com (213-243-189-158.bb.dnainternet.fi [213.243.189.158]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 9DE29842; Wed, 29 Nov 2023 11:23:51 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1701253431; bh=Y6AJ/kPLyDOivircGV4x/fYC3/RvS1k47yzPnXLdMyY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=oqdRt6owFMYgaCAV7pN799tF/mF11HYqekY+EQzfpOGqTL4rLzkdOJkis1PKVuI/C QLrBkvODzfLuGVblA56vejCHbZcza/M/V+rQf+Usxfj+KRqvVn41jkyD/gCBFqvRJJ ZLbM9hCj61pwJI4w8W/KDaVEsHalLLAOCSnKEV9U= Date: Wed, 29 Nov 2023 12:24:34 +0200 From: Laurent Pinchart To: Tomasz Figa Cc: Benjamin Gaignard , hverkuil@xs4all.nl, mchehab@kernel.org, m.szyprowski@samsung.com, matt.ranostay@konsulko.com, linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, linux-staging@lists.linux.dev, kernel@collabora.com, Shawn Guo , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , NXP Linux Team Subject: Re: [PATCH 07/55] media: imx8-isi: Stop abusing of min_buffers_needed field Message-ID: <20231129102434.GD18109@pendragon.ideasonboard.com> References: <20231127165454.166373-1-benjamin.gaignard@collabora.com> <20231127165454.166373-8-benjamin.gaignard@collabora.com> <20231127170700.GC31314@pendragon.ideasonboard.com> <6fa1ec09-3e30-475e-9718-29d23586753e@collabora.com> <995eb6c2-cc7f-4217-bc37-4ab1a32f36ee@collabora.com> Precedence: bulk X-Mailing-List: linux-media@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: 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 > > >>>>>> CC: Laurent Pinchart > > >>>>>> CC: Mauro Carvalho Chehab > > >>>>>> CC: Shawn Guo > > >>>>>> CC: Sascha Hauer > > >>>>>> CC: Pengutronix Kernel Team > > >>>>>> CC: Fabio Estevam > > >>>>>> CC: NXP Linux Team > > >>>>>> --- > > >>>>>> 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