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From: Stanimir Varbanov <stanimir.varbanov@linaro.org>
To: Hans Verkuil <hverkuil@xs4all.nl>,
	Tomasz Figa <tfiga@chromium.org>,
	Stanimir Varbanov <stanimir.varbanov@linaro.org>
Cc: Linux Media Mailing List <linux-media@vger.kernel.org>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	linux-arm-msm <linux-arm-msm@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] media/doc: Allow sizeimage to be set by v4l clients
Date: Thu, 16 May 2019 18:09:35 +0300
Message-ID: <49fd2002-8723-2f00-c972-8d605561b29a@linaro.org> (raw)
In-Reply-To: <cd7baea0-3893-7471-2e86-9cc6730843e3@xs4all.nl>

Hi Hans,

On 5/16/19 1:40 PM, Hans Verkuil wrote:
> On 5/16/19 11:56 AM, Tomasz Figa wrote:
>> On Thu, May 16, 2019 at 5:09 PM Stanimir Varbanov
>> <stanimir.varbanov@linaro.org> wrote:
>>>
>>> Hi Hans,
>>>
>>> On 5/14/19 11:54 AM, Hans Verkuil wrote:
>>>> Hi Stanimir,
>>>>
>>>> On 4/12/19 5:59 PM, Stanimir Varbanov wrote:
>>>>> This changes v4l2_pix_format and v4l2_plane_pix_format sizeimage
>>>>> field description to allow v4l clients to set bigger image size
>>>>> in case of variable length compressed data.
>>>>
>>>> I've been reconsidering this change. The sizeimage value in the format
>>>> is the minimum size a buffer should have in order to store the data of
>>>> an image of the width and height as described in the format.
>>>>
>>>> But there is nothing that prevents userspace from calling VIDIOC_CREATEBUFS
>>>> instead of VIDIOC_REQBUFS to allocate larger buffers.
>>>
>>> Sometimes CREATEBUFS cannot be implemented for a particular fw/hw.
>>>
>>> CC: Tomasz for his opinion.
>>>
>>
>> Thanks Stanimir.
>>
>> Actually, if called at the same point in time as REQBUFS, CREATE_BUFS
>> doesn't really differ to much, except that it gives more flexibility
>> for allocating the buffers and that shouldn't depend on any specific
>> features of hardware or firmware.
>>
>> Actually, one could even allocate any buffers any time regardless of
>> hardware/firmware support, but the ability to use such buffers would
>> actually depend on such.
>>
>> Perhaps we should just let the drivers return -EBUSY from CREATE_BUFS
>> if called at the wrong time?
>>
>>>>
>>>> So do we really need this change?
>>>>
>>
>> Yes, because this has worked like this all the time, but it was just
>> not documented. Disallowing this would break quite a bit of existing
>> userspace.
> 
> Which drivers allow this today? I think that would be useful information
> for the commit log of a v4 of this patch.
> 

I'd say s5p-mfc and mtk-vcodec at least.

-- 
regards,
Stan

      reply index

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-12 15:59 Stanimir Varbanov
2019-05-02 12:55 ` Mauro Carvalho Chehab
2019-05-02 13:16   ` Hans Verkuil
2019-05-02 13:29     ` Mauro Carvalho Chehab
2019-05-07 16:54       ` Stanimir Varbanov
2019-05-14  8:54 ` Hans Verkuil
2019-05-14 12:19   ` Nicolas Dufresne
2019-05-14 12:23     ` Hans Verkuil
2019-05-16  8:09   ` Stanimir Varbanov
2019-05-16  9:56     ` Tomasz Figa
2019-05-16 10:40       ` Hans Verkuil
2019-05-16 15:09         ` Stanimir Varbanov [this message]

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