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Date: Fri, 31 May 2024 09:28:25 +0200
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Subject: Re: [PATCH v2] media: uapi: v4l: Change V4L2_TYPE_IS_CAPTURE
 condition
To: Nas Chung <nas.chung@chipsnmedia.com>,
 "mchehab@kernel.org" <mchehab@kernel.org>,
 "linux-media@vger.kernel.org" <linux-media@vger.kernel.org>,
 "sebastian.fricke@collabora.com" <sebastian.fricke@collabora.com>,
 "m.tretter@pengutronix.de" <m.tretter@pengutronix.de>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <20240528020425.4994-1-nas.chung@chipsnmedia.com>
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 <SL2P216MB1246D6779BDDA2C03333D549FBFC2@SL2P216MB1246.KORP216.PROD.OUTLOOK.COM>
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From: Hans Verkuil <hverkuil@xs4all.nl>
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On 31/05/2024 09:03, Nas Chung wrote:
> Hi, Hans.
> 
>> -----Original Message-----
>> From: Hans Verkuil <hverkuil@xs4all.nl>
>> Sent: Thursday, May 30, 2024 7:32 PM
>> To: Nas Chung <nas.chung@chipsnmedia.com>; mchehab@kernel.org; linux-
>> media@vger.kernel.org; sebastian.fricke@collabora.com;
>> m.tretter@pengutronix.de
>> Cc: linux-kernel@vger.kernel.org
>> Subject: Re: [PATCH v2] media: uapi: v4l: Change V4L2_TYPE_IS_CAPTURE
>> condition
>>
>> On 28/05/2024 04:04, Nas Chung wrote:
>>> Explicitly compare a buffer type only with valid buffer types,
>>> to avoid matching the buffer type outside of valid buffer
>>> type set.
>>>
>>> Signed-off-by: Nas Chung <nas.chung@chipsnmedia.com>
>>> ---
>>>  include/uapi/linux/videodev2.h | 7 ++++++-
>>>  1 file changed, 6 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/include/uapi/linux/videodev2.h
>> b/include/uapi/linux/videodev2.h
>>> index fe6b67e83751..fa2b7086e480 100644
>>> --- a/include/uapi/linux/videodev2.h
>>> +++ b/include/uapi/linux/videodev2.h
>>> @@ -157,6 +157,10 @@ enum v4l2_buf_type {
>>>  	V4L2_BUF_TYPE_PRIVATE              = 0x80,
>>>  };
>>>
>>> +#define V4L2_TYPE_IS_VALID(type)		\
>>> +	((type) >= V4L2_BUF_TYPE_VIDEO_CAPTURE	\
>>> +	 && (type) <= V4L2_BUF_TYPE_META_OUTPUT)
>>> +
>>>  #define V4L2_TYPE_IS_MULTIPLANAR(type)			\
>>>  	((type) == V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE	\
>>>  	 || (type) == V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE)
>>> @@ -171,7 +175,8 @@ enum v4l2_buf_type {
>>>  	 || (type) == V4L2_BUF_TYPE_SDR_OUTPUT			\
>>>  	 || (type) == V4L2_BUF_TYPE_META_OUTPUT)
>>>
>>> -#define V4L2_TYPE_IS_CAPTURE(type) (!V4L2_TYPE_IS_OUTPUT(type))
>>> +#define V4L2_TYPE_IS_CAPTURE(type)	\
>>> +	(V4L2_TYPE_IS_VALID(type) && !V4L2_TYPE_IS_OUTPUT(type))
>>>
>>>  enum v4l2_tuner_type {
>>>  	V4L2_TUNER_RADIO	     = 1,
>>
>> This patch introduced this warning:
>>
>> In function 'find_format_by_index',
>>    inlined from 'vdec_enum_fmt' at
>> drivers/media/platform/qcom/venus/vdec.c:452:8:
>> drivers/media/platform/qcom/venus/vdec.c:172:32: warning: 'valid' may be
>> used uninitialized [-Wmaybe-uninitialized]
>>  172 |                 if (k == index && valid)
>>      |                     ~~~~~~~~~~~^~~~~~~~
>> drivers/media/platform/qcom/venus/vdec.c: In function 'vdec_enum_fmt':
>> drivers/media/platform/qcom/venus/vdec.c:157:22: note: 'valid' was
>> declared here
>>  157 |                 bool valid;
>>      |                      ^~~~~
>>
>> This driver does this:
>>
>> 	bool valid;
>>
>>        if (V4L2_TYPE_IS_OUTPUT(type)) {
>>                valid = venus_helper_check_codec(inst, fmt[i].pixfmt);
>>        } else if (V4L2_TYPE_IS_CAPTURE(type)) {
>>                valid = venus_helper_check_format(inst, fmt[i].pixfmt);
>>
>> With your patch both V4L2_TYPE_IS_OUTPUT(type) and
>> V4L2_TYPE_IS_CAPTURE(type)
>> can return false, something that wasn't possible without this patch.
>>
>> In this driver the fix would just be to drop the second 'if' altogether,
>> so just
>> '} else {'.
>>
>> Since these defines are part of the public API, this change introduces a
>> subtle
>> behavior difference that can affect applications.
> 
> Thank you for a detailed description.
> 
>>
>> That said, I do consider this an improvement.
>>
>> I would like some changes, though:
>>
>> 1) Just after "V4L2_BUF_TYPE_META_OUTPUT          = 14," in enum
>> v4l2_buf_type,
>>   add a comment saying that V4L2_TYPE_IS_VALID and (for output types)
>>   V4L2_TYPE_IS_OUTPUT must be updated if a new type is added. It's all
>>   too easy to forget that otherwise.
> 
>> 2) Add a patch fixing the venus/vdec.c code.
> 
> 1), 2) I will address both in v3.
> 
>> 3) Something else I noticed, but I think this change should be in a
>> separate patch:
>>   V4L2_TYPE_IS_OUTPUT() returns true for V4L2_BUF_TYPE_VIDEO_OVERLAY, but
>> that
>>   definitely belongs to CAPTURE. Nobody really uses that type anymore,
>> but still,
>>   it should be fixed.
> 
> 3) Would you prefer this modification to be included as a separate patch
> in the v3 of this patch series, or should it be submitted as a new
> standalone patch ?

Separate patch in this series, please.

Regards,

	Hans

> 
> Thanks.
> Nas.
> 
>>
>> Regards,
>>
>> 	Hans
>