linux-kernel - Re: [PATCH 07/55] media: imx8-isi: Stop abusing of min_buffers

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Message-ID: <6fa1ec09-3e30-475e-9718-29d23586753e@collabora.com>
Date:   Tue, 28 Nov 2023 10:31:45 +0100
From:   Benjamin Gaignard <benjamin.gaignard@...labora.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     hverkuil@...all.nl, mchehab@...nel.org, tfiga@...omium.org,
        m.szyprowski@...sung.com, matt.ranostay@...sulko.com,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        linux-staging@...ts.linux.dev, kernel@...labora.com,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>
Subject: Re: [PATCH 07/55] media: imx8-isi: Stop abusing of min_buffers_needed
 field


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 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@...labora.com>
>> CC: Laurent Pinchart <laurent.pinchart@...asonboard.com>
>> CC: Mauro Carvalho Chehab <mchehab@...nel.org>
>> CC: Shawn Guo <shawnguo@...nel.org>
>> CC: Sascha Hauer <s.hauer@...gutronix.de>
>> CC: Pengutronix Kernel Team <kernel@...gutronix.de>
>> CC: Fabio Estevam <festevam@...il.com>
>> CC: NXP Linux Team <linux-imx@....com>
>> ---
>>   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;
>>