RE: [PATCH v2] media: uapi: v4l: Change V4L2_TYPE_IS_CAPTURE condition

[Nas Chung]

Hi, Hans.

>-----Original Message-----
>From: Hans Verkuil <hverkuil@xxxxxxxxx>
>Sent: Thursday, May 30, 2024 7:32 PM
>To: Nas Chung <nas.chung@xxxxxxxxxxxxxxx>; mchehab@xxxxxxxxxx; linux-
>media@xxxxxxxxxxxxxxx; sebastian.fricke@xxxxxxxxxxxxx;
>m.tretter@xxxxxxxxxxxxxx
>Cc: linux-kernel@xxxxxxxxxxxxxxx
>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@xxxxxxxxxxxxxxx>
>> ---
>>  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 ?

Thanks.
Nas.

>
>Regards,
>
>	Hans