Le 29/11/2023 à 05:17, Tomasz Figa a écrit :
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?
Just because the hardware needs the physical address of the buffer to access it.
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.
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.
Regards,
Benjamin
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;
