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Message-ID: <d48f71b4-327c-4fe0-99b4-a48f48f3f1e2@xs4all.nl>
Date: Sat, 20 Jul 2024 10:40:16 +0200
From: Hans Verkuil <hverkuil-cisco@...all.nl>
To: Benjamin Gaignard <benjamin.gaignard@...labora.com>, mchehab@...nel.org,
ezequiel@...guardiasur.com.ar
Cc: 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
On 19/07/2024 15:15, Hans Verkuil wrote:
> On 17/07/2024 15:14, 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.
>>
>> 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;
>>
>> 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
>
> For reasons mentioned earlier, you cannot make the flags field an input to the
> driver, that will almost certainly break some applications that do not zero
> the flags field today, since they expect it to be set by the driver.
>
> What probably will work is to add a flag to the index field: this would be
> similar to what I do in VIDIOC_QUERYCTRL where you can OR the id field with
> V4L2_CTRL_FLAG_NEXT_CTRL to modify the behavior.
>
> It is perfectly fine to use the top bits of the index for this.
>
> Drivers that do not support this will just fail with EINVAL, and drivers that
> do support this will return a proper format.
>
> Applications can easily test support for this by just calling ENUM_FMT with 0
> ORed with the new flag: if it is supported, then it will return 0, otherwise
> -EINVAL.
>
> With this scheme I think you can also drop the proposed V4L2_FMT_FLAG_ALL_FORMATS
> flag.
Please note that this is an addition to the uAPI, so this also implies that
there should be patches for v4l-utils (v4l2-ctl and v4l2-compliance) and
ideally patches for one or more of the media test-drivers to implement this
flag. Together with v4l2-compliance that will ensure that the new flag is
actually tested by the regression tests.
Regards,
Hans
>
> But as I mentioned in my reply to the cover letter of this series, I am not
> convinced we really need this, and if we do, then I am not convinced about
> the name of the flag.
>
> And I would also like to know if such a feature can be used by m2m drivers
> that are not codecs (e.g. scalers, csc converters), and if that would impact
> the name/description of the flag.
>
> It is currently very specific for decoders, but I prefer to see a more general
> solution, not just for one specific corner case.
>
> Regards,
>
> Hans
>
>>
>> /* Frame Size and frame rate enumeration */
>> /*
>
>
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