linux-kernel - Re: [PATCH v11 45/56] media: test-drivers: vivid: Increase max supported buffers for capture queues

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Message-ID: <953e9c30-0060-45b7-b6e3-8f03d331b6b8@xs4all.nl>
Date:   Mon, 16 Oct 2023 16:33:09 +0200
From:   Hans Verkuil <hverkuil-cisco@...all.nl>
To:     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,
        nicolas.dufresne@...labora.com
Cc:     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
Subject: Re: [PATCH v11 45/56] media: test-drivers: vivid: Increase max
 supported buffers for capture queues

On 16/10/2023 16:20, Benjamin Gaignard wrote:
> 
> Le 16/10/2023 à 12:32, Hans Verkuil a écrit :
>> On 12/10/2023 13:46, Benjamin Gaignard wrote:
>>> Change the maximum number of buffers of some capture queues in order
>>> to test max_num_buffers field.
>>>
>>> Allow to allocate up to:
>>> - 64 buffers for video capture queue.
>>> - 1024 buffers for sdr capture queue.
>>> - 32768 buffers for vbi capture queue.
>>>
>>> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...labora.com>
>>> ---
>>>   drivers/media/test-drivers/vivid/vivid-core.c | 7 +++++++
>>>   1 file changed, 7 insertions(+)
>>>
>>> diff --git a/drivers/media/test-drivers/vivid/vivid-core.c b/drivers/media/test-drivers/vivid/vivid-core.c
>>> index 394c9f81ea72..b5656330578d 100644
>>> --- a/drivers/media/test-drivers/vivid/vivid-core.c
>>> +++ b/drivers/media/test-drivers/vivid/vivid-core.c
>>> @@ -876,6 +876,13 @@ static int vivid_create_queue(struct vivid_dev *dev,
>>>       q->type = buf_type;
>>>       q->io_modes = VB2_MMAP | VB2_DMABUF;
>>>       q->io_modes |= V4L2_TYPE_IS_OUTPUT(buf_type) ?  VB2_WRITE : VB2_READ;
>>> +    if (buf_type == V4L2_BUF_TYPE_VIDEO_CAPTURE)
>>> +        q->max_num_buffers = 64;
>>> +    if (buf_type == V4L2_BUF_TYPE_SDR_CAPTURE)
>>> +        q->max_num_buffers = 1024;
>>> +    if (buf_type == V4L2_BUF_TYPE_VBI_CAPTURE)
>>> +        q->max_num_buffers = 32768;
>> This should use the same calculation as MAX_BUFFER_INDEX.
>>
>> I wonder if those defines should move to videobuf2-core.h instead.
> 
> I'm not sure about what you want here, q->max_num_buffers is clamped in vb2_core_queue_init():
> 
> /* The maximum is limited by offset cookie encoding pattern */
> q->max_num_buffers = min_t(unsigned int, q->max_num_buffers, MAX_BUFFER_INDEX);
> 
> Do you want to reuse MAX_BUFFER_INDEX for these drivers ?

Ah, I forgot about the clamping.

Add a comment like this:

/*
 * The maximum number of buffers is 32768 if PAGE_SHIFT == 12,
 * see also MAX_BUFFER_INDEX in videobuf2-core.c. It will be less if
 * PAGE_SHIFT > 12, but then max_num_buffers will be clamped by
 * videobuf2-core.c to MAX_BUFFER_INDEX.
 */

Regards,

	Hans

> 
> Regards,
> Benjamin
> 
>>
>> Regards,
>>
>>     Hans
>>
>>> +
>>>       if (allocators[dev->inst] != 1)
>>>           q->io_modes |= VB2_USERPTR;
>>>       q->drv_priv = dev;
>>