linux-kernel - Re: [PATCH v14 35/56] media: cedrus: Stop direct calls to queue num

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Date:   Thu, 9 Nov 2023 16:48:33 +0100
From:   Andrzej Pietrasiewicz <andrzej.p@...labora.com>
To:     Paul Kocialkowski <paul.kocialkowski@...tlin.com>
Cc:     Benjamin Gaignard <benjamin.gaignard@...labora.com>,
        mchehab@...nel.org, tfiga@...omium.org, m.szyprowski@...sung.com,
        ming.qian@....com, ezequiel@...guardiasur.com.ar,
        p.zabel@...gutronix.de, gregkh@...uxfoundation.org,
        hverkuil-cisco@...all.nl, nicolas.dufresne@...labora.com,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-arm-msm@...r.kernel.org,
        linux-rockchip@...ts.infradead.org, linux-staging@...ts.linux.dev,
        kernel@...labora.com, Maxime Ripard <mripard@...nel.org>
Subject: Re: [PATCH v14 35/56] media: cedrus: Stop direct calls to queue
 num_buffers field

Hi Paul,

W dniu 9.11.2023 o 15:14, Paul Kocialkowski pisze:
> Hi Andrzej,
> 
> On Thu 09 Nov 23, 12:27, Andrzej Pietrasiewicz wrote:
>> Hi Paul,
>>
>> W dniu 31.10.2023 o 17:30, Benjamin Gaignard pisze:
>>> Use vb2_get_num_buffers() to avoid using queue num_buffers field directly.
>>> This allows us to change how the number of buffers is computed in the
>>> future.
>>>
>>> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...labora.com>
>>> Acked-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>
>>
>> Given you've alaredy A-b, would you be ok with adding this sentence:
>>
>> "While at it, check the return value of vb2_get_buffer()."
>>
>> to the commit message body?
> 
> Not only do I agree, but because this is done in a function returning void,
> you could even:
> 
> if (WARN_ON(!vb))
> 	continue;
> 
> so that it doesn't go completely unnoticed.
> 
> What do you think?
> 

I'd ask Benjamin.

But my take on the direction of changes is that ultimately
there will be "holes" in the array of allocated buffers (hence the
bitmap to track which slots are used and which are not). In other words,
getting a NULL sometimes will be an expected situation, and a WARN() will
not be appropriate for an expected situation.

@Benjamin?

Regards,

Andrzej

> Cheers,
> 
> Paul
> 
>> @Benjamin:
>>
>> With this change, you can add my
>>
>> Reviewed-by: Andrzej Pietrasiewicz <andrzej.p@...labora.com>
>>
>>> CC: Maxime Ripard <mripard@...nel.org>
>>> ---
>>>    drivers/staging/media/sunxi/cedrus/cedrus_h264.c | 9 +++++++--
>>>    drivers/staging/media/sunxi/cedrus/cedrus_h265.c | 9 +++++++--
>>>    2 files changed, 14 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_h264.c b/drivers/staging/media/sunxi/cedrus/cedrus_h264.c
>>> index dfb401df138a..3e2843ef6cce 100644
>>> --- a/drivers/staging/media/sunxi/cedrus/cedrus_h264.c
>>> +++ b/drivers/staging/media/sunxi/cedrus/cedrus_h264.c
>>> @@ -653,8 +653,13 @@ static void cedrus_h264_stop(struct cedrus_ctx *ctx)
>>>    	vq = v4l2_m2m_get_vq(ctx->fh.m2m_ctx, V4L2_BUF_TYPE_VIDEO_CAPTURE);
>>> -	for (i = 0; i < vq->num_buffers; i++) {
>>> -		buf = vb2_to_cedrus_buffer(vb2_get_buffer(vq, i));
>>> +	for (i = 0; i < vb2_get_num_buffers(vq); i++) {
>>> +		struct vb2_buffer *vb = vb2_get_buffer(vq, i);
>>> +
>>> +		if (!vb)
>>> +			continue;
>>> +
>>> +		buf = vb2_to_cedrus_buffer(vb);
>>>    		if (buf->codec.h264.mv_col_buf_size > 0) {
>>>    			dma_free_attrs(dev->dev,
>>> diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_h265.c b/drivers/staging/media/sunxi/cedrus/cedrus_h265.c
>>> index fc9297232456..52e94c8f2f01 100644
>>> --- a/drivers/staging/media/sunxi/cedrus/cedrus_h265.c
>>> +++ b/drivers/staging/media/sunxi/cedrus/cedrus_h265.c
>>> @@ -869,8 +869,13 @@ static void cedrus_h265_stop(struct cedrus_ctx *ctx)
>>>    	vq = v4l2_m2m_get_vq(ctx->fh.m2m_ctx, V4L2_BUF_TYPE_VIDEO_CAPTURE);
>>> -	for (i = 0; i < vq->num_buffers; i++) {
>>> -		buf = vb2_to_cedrus_buffer(vb2_get_buffer(vq, i));
>>> +	for (i = 0; i < vb2_get_num_buffers(vq); i++) {
>>> +		struct vb2_buffer *vb = vb2_get_buffer(vq, i);
>>> +
>>> +		if (!vb)
>>> +			continue;
>>> +
>>> +		buf = vb2_to_cedrus_buffer(vb);
>>>    		if (buf->codec.h265.mv_col_buf_size > 0) {
>>>    			dma_free_attrs(dev->dev,
>>
> 
> 
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