linux-kernel - Re: [PATCH 27/55] media: sun6i-isp: Stop abusing of min_buffers

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Date:   Wed, 29 Nov 2023 15:03:20 +0100
From:   Benjamin Gaignard <benjamin.gaignard@...labora.com>
To:     Paul Kocialkowski <paul.kocialkowski@...tlin.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,
        Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Samuel Holland <samuel@...lland.org>,
        linux-sunxi@...ts.linux.dev
Subject: Re: [PATCH 27/55] media: sun6i-isp: Stop abusing of
 min_buffers_needed field


Le 29/11/2023 à 14:40, Paul Kocialkowski a écrit :
> Hi Benjamin,
>
> On Mon 27 Nov 23, 17:54, Benjamin Gaignard wrote:
>> 'min_buffers_needed' is suppose to be used to indicate the number
>> of buffers needed by DMA engine to start streaming.
>> sun6i-isp driver doesn't use DMA engine and just want to specify
>> the minimum number of buffers to allocate when calling VIDIOC_REQBUFS.
>> That 'min_reqbufs_allocation' field purpose so use it.
> The hardware actually has its own DMA engine. It can work with just one buffer
> though (which will never be returned to userspace). But I think we should still
> require at least two buffers allocated, otherwise the driver will be of no use
> at all.
>
> So I don't think the commit message here is correct.

That is exactly the info I hope to get for this first series since I don't know
each hardware block details.
I will remove this commit and make the driver use min_queued_buffers field instead
so that will fit with it needs.

Thanks,
Benjamin

>
> Cheers,
>
> Paul
>
>> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...labora.com>
>> CC: Paul Kocialkowski <paul.kocialkowski@...tlin.com>
>> CC: Chen-Yu Tsai <wens@...e.org>
>> CC: Jernej Skrabec <jernej.skrabec@...il.com>
>> CC: Samuel Holland <samuel@...lland.org>
>> CC: linux-sunxi@...ts.linux.dev
>> ---
>>   drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_capture.c | 2 +-
>>   drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_params.c  | 2 +-
>>   2 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_capture.c b/drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_capture.c
>> index 1595a9607775..f47f9946c19f 100644
>> --- a/drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_capture.c
>> +++ b/drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_capture.c
>> @@ -660,7 +660,7 @@ int sun6i_isp_capture_setup(struct sun6i_isp_device *isp_dev)
>>   	queue->buf_struct_size = sizeof(struct sun6i_isp_buffer);
>>   	queue->ops = &sun6i_isp_capture_queue_ops;
>>   	queue->mem_ops = &vb2_dma_contig_memops;
>> -	queue->min_buffers_needed = 2;
>> +	queue->min_reqbufs_allocation = 2;
>>   	queue->timestamp_flags = V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC;
>>   	queue->lock = &capture->lock;
>>   	queue->dev = isp_dev->dev;
>> diff --git a/drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_params.c b/drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_params.c
>> index e28be895b486..259f6bfcb620 100644
>> --- a/drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_params.c
>> +++ b/drivers/staging/media/sunxi/sun6i-isp/sun6i_isp_params.c
>> @@ -489,7 +489,7 @@ int sun6i_isp_params_setup(struct sun6i_isp_device *isp_dev)
>>   	queue->buf_struct_size = sizeof(struct sun6i_isp_buffer);
>>   	queue->ops = &sun6i_isp_params_queue_ops;
>>   	queue->mem_ops = &vb2_vmalloc_memops;
>> -	queue->min_buffers_needed = 1;
>> +	queue->min_reqbufs_allocation = 1;
>>   	queue->timestamp_flags = V4L2_BUF_FLAG_TIMESTAMP_MONOTONIC;
>>   	queue->lock = &params->lock;
>>   	queue->dev = isp_dev->dev;
>> -- 
>> 2.39.2
>>