Message-ID: <1faa7098-b108-480e-ae4b-ed25e0020e51@collabora.com>
Date: Thu, 18 Jul 2024 09:04:24 +0200
From: Benjamin Gaignard <benjamin.gaignard@...labora.com>
To: Nicolas Dufresne <nicolas@...fresne.ca>,
 Jacopo Mondi <jacopo.mondi@...asonboard.com>
Cc: mchehab@...nel.org, ezequiel@...guardiasur.com.ar,
 hverkuil-cisco@...all.nl, linux-media@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-rockchip@...ts.infradead.org,
 kernel@...labora.com
Subject: Re: [PATCH v4 1/2] media: videodev2: Add flags to unconditionnaly
 enumerate pixels formats


Le 17/07/2024 à 19:50, Nicolas Dufresne a écrit :
> Hi
>
> Le mercredi 17 juillet 2024 à 16:04 +0200, Jacopo Mondi a écrit :
>> Hi Benjamin
>>
>> On Wed, Jul 17, 2024 at 03:44:24PM GMT, Benjamin Gaignard wrote:
>>> Le 17/07/2024 à 15:20, Jacopo Mondi a écrit :
>>>> Hi Benjamin
>>>>
>>>> On Wed, Jul 17, 2024 at 03:14:29PM GMT, Benjamin Gaignard wrote:
>>>>> Add new flags to enumerate all pixels formats when calling VIDIOC_ENUM_FMT ioctl.
>>>>> When this V4L2_FMT_FLAG_ENUM_ALL_FORMATS flag is set drivers must
>>>>> ignore the configuration and return the hardware supported pixel
>>>>> formats for the specified queue.
>>>>> To distinguish this particular enumeration case V4L2_FMT_FLAG_ALL_FORMATS
>>>>> flag must be set by the drivers to highlight support of this feature
>>>>> to user space applications.
>>>>> This will permit to discover which pixel formats are supported
>>>>> without setting codec-specific information so userland can more easily
>>>>> know if the driver suits its needs well.
>>>>> The main target are stateless decoders so update the documentation
>>>>> about how to use this flag.
>>>>>
>>>>> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@...labora.com>
>>>>> ---
>>>>> changes in version 4:
>>>>> - Explicitly document that the new flags are targeting mem2mem devices.
>>>>>
>>>>>    .../userspace-api/media/v4l/dev-stateless-decoder.rst |  6 ++++++
>>>>>    .../userspace-api/media/v4l/vidioc-enum-fmt.rst       | 11 +++++++++++
>>>>>    .../userspace-api/media/videodev2.h.rst.exceptions    |  2 ++
>>>>>    drivers/media/v4l2-core/v4l2-ioctl.c                  |  3 +++
>>>>>    include/uapi/linux/videodev2.h                        |  2 ++
>>>>>    5 files changed, 24 insertions(+)
>>>>>
>>>>> diff --git a/Documentation/userspace-api/media/v4l/dev-stateless-decoder.rst b/Documentation/userspace-api/media/v4l/dev-stateless-decoder.rst
>>>>> index 35ed05f2695e..b0b657de910d 100644
>>>>> --- a/Documentation/userspace-api/media/v4l/dev-stateless-decoder.rst
>>>>> +++ b/Documentation/userspace-api/media/v4l/dev-stateless-decoder.rst
>>>>> @@ -58,6 +58,12 @@ Querying capabilities
>>>>>         default values for these controls being used, and a returned set of formats
>>>>>         that may not be usable for the media the client is trying to decode.
>>>>>
>>>>> +   * If the ``V4L2_FMT_FLAG_ENUM_ALL_FORMATS`` flag is set the driver must enumerate
>>>>> +     all the supported formats without taking care of codec-dependent controls
>>>>> +     set on the ``OUTPUT`` queue. To indicate that the driver has take care of this
>>>>> +     flag it must set ``V4L2_FMT_FLAG_ALL_FORMATS`` flag for each format while
>>>>> +     enumerating.
>>>>> +
>>>>>    3. The client may use :c:func:`VIDIOC_ENUM_FRAMESIZES` to detect supported
>>>>>       resolutions for a given format, passing desired pixel format in
>>>>>       :c:type:`v4l2_frmsizeenum`'s ``pixel_format``.
>>>>> diff --git a/Documentation/userspace-api/media/v4l/vidioc-enum-fmt.rst b/Documentation/userspace-api/media/v4l/vidioc-enum-fmt.rst
>>>>> index 3adb3d205531..15bc2f59c05a 100644
>>>>> --- a/Documentation/userspace-api/media/v4l/vidioc-enum-fmt.rst
>>>>> +++ b/Documentation/userspace-api/media/v4l/vidioc-enum-fmt.rst
>>>>> @@ -234,6 +234,17 @@ the ``mbus_code`` field is handled differently:
>>>>>    	valid. The buffer consists of ``height`` lines, each having ``width``
>>>>>    	Data Units of data and the offset (in bytes) between the beginning of
>>>>>    	each two consecutive lines is ``bytesperline``.
>>>>> +    * - ``V4L2_FMT_FLAG_ENUM_ALL_FORMATS``
>>>>> +      - 0x0400
>>>>> +      - Set by userland applications to enumerate all possible pixel formats
>>>>> +        without taking care of any OUTPUT or CAPTURE queue configuration.
>>>>> +        This flag is relevant only for mem2mem devices.
>>>>> +    * - ``V4L2_FMT_FLAG_ALL_FORMATS``
>>>>> +      - 0x0800
>>>>> +      - Set by the driver to indicated that format have been enumerated because
>>>>> +        :ref:`V4L2_FMT_FLAG_ENUM_ALL_FORMATS <v4l2-pix-fmt-flag-set-csc>` has
>>>>> +        been set by the userland application.
>>>>> +        This flag is relevant only for mem2mem devices.
>>>> Thanks, however I think this can be wrapper on the previous line
>>> ok
>>>
>>>>>    Return Value
>>>>>    ============
>>>>> diff --git a/Documentation/userspace-api/media/videodev2.h.rst.exceptions b/Documentation/userspace-api/media/videodev2.h.rst.exceptions
>>>>> index bdc628e8c1d6..7a3a1e9dc055 100644
>>>>> --- a/Documentation/userspace-api/media/videodev2.h.rst.exceptions
>>>>> +++ b/Documentation/userspace-api/media/videodev2.h.rst.exceptions
>>>>> @@ -216,6 +216,8 @@ replace define V4L2_FMT_FLAG_CSC_YCBCR_ENC fmtdesc-flags
>>>>>    replace define V4L2_FMT_FLAG_CSC_HSV_ENC fmtdesc-flags
>>>>>    replace define V4L2_FMT_FLAG_CSC_QUANTIZATION fmtdesc-flags
>>>>>    replace define V4L2_FMT_FLAG_META_LINE_BASED fmtdesc-flags
>>>>> +replace define V4L2_FMT_FLAG_ENUM_ALL_FORMATS fmtdesc-flags
>>>>> +replace define V4L2_FMT_FLAG_ALL_FORMATS fmtdesc-flags
>>>>>
>>>>>    # V4L2 timecode types
>>>>>    replace define V4L2_TC_TYPE_24FPS timecode-type
>>>>> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
>>>>> index 4c76d17b4629..5785a98b6ba2 100644
>>>>> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
>>>>> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
>>>>> @@ -1569,6 +1569,7 @@ static int v4l_enum_fmt(const struct v4l2_ioctl_ops *ops,
>>>>>    	int ret = check_fmt(file, p->type);
>>>>>    	u32 mbus_code;
>>>>>    	u32 cap_mask;
>>>>> +	u32 flags;
>>>>>
>>>>>    	if (ret)
>>>>>    		return ret;
>>>>> @@ -1578,8 +1579,10 @@ static int v4l_enum_fmt(const struct v4l2_ioctl_ops *ops,
>>>>>    		p->mbus_code = 0;
>>>>>
>>>>>    	mbus_code = p->mbus_code;
>>>>> +	flags = p->flags & V4L2_FMT_FLAG_ENUM_ALL_FORMATS;
>>>>>    	memset_after(p, 0, type);
>>>>>    	p->mbus_code = mbus_code;
>>>>> +	p->flags = flags;
>>>> Won't this set V4L2_FMT_FLAG_ENUM_ALL_FORMATS (if present) in the
>>>> flags returned to userspace ? Shouldn't be drivers to set
>>>> V4L2_FMT_FLAG_ALL_FORMATS instead ?
>>> memset_after zeroed flags field so we need this to send V4L2_FMT_FLAG_ENUM_ALL_FORMATS
>>> flag to drivers. Return it to userspace is a side effect but I don't that is problem
>>> since it set it anyway.
>>>
>> Ok, if the expectation is that the flag is preserved through the ioctl
>> call, this is fine with me
> I might be missing something other similar features are explicitly advertised by
> drivers. This way, the generic layer can keep or clear the flag based of if its
> supported. The fact the flag persist the ioctl() or not endup having a useful
> semantic.
>
> Could we do the same?

It is the only flag set by userspace when calling the ioctl(), all others
are set by the drivers.
I can clean it from the ioctl() structure after driver call but that won't change anything.

>
>> Reviewed-by: Jacopo Mondi <jacopo.mondi@...asonboard.com>
>>
>>>>>    	switch (p->type) {
>>>>>    	case V4L2_BUF_TYPE_VIDEO_CAPTURE:
>>>>> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
>>>>> index fe6b67e83751..b6a5da79ba21 100644
>>>>> --- a/include/uapi/linux/videodev2.h
>>>>> +++ b/include/uapi/linux/videodev2.h
>>>>> @@ -886,6 +886,8 @@ struct v4l2_fmtdesc {
>>>>>    #define V4L2_FMT_FLAG_CSC_HSV_ENC		V4L2_FMT_FLAG_CSC_YCBCR_ENC
>>>>>    #define V4L2_FMT_FLAG_CSC_QUANTIZATION		0x0100
>>>>>    #define V4L2_FMT_FLAG_META_LINE_BASED		0x0200
>>>>> +#define V4L2_FMT_FLAG_ENUM_ALL_FORMATS		0x0400
>>>>> +#define V4L2_FMT_FLAG_ALL_FORMATS		0x0800
>>>>>
>>>>>    	/* Frame Size and frame rate enumeration */
>>>>>    /*
>>>>> --
>>>>> 2.43.0
>>>>>
>>>>>
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