On 6/11/19 10:13 AM, Hans Verkuil wrote:
> On 6/9/19 4:38 PM, Maxime Jourdan wrote:
>> Hello,
>>
>> This RFC proposes a new format flag - V4L2_FMT_FLAG_DYN_RESOLUTION - used
>> to tag coded formats for which the device supports dynamic resolution
>> switching, via V4L2_EVENT_SOURCE_CHANGE.
>> This includes the initial "source change" where the device is able to
>> tell userspace about the coded resolution and the DPB size (which
>> sometimes translates to V4L2_CID_MIN_BUFFERS_FOR_CAPTURE).
>
> Shouldn't the initial source change still be there? The amlogic decoder
> is capable of determining the resolution of the stream, right? It just
> can't handle mid-stream changes.
I've been thinking about this a bit more: there are three different HW
capabilities:
1) The hardware cannot parse the resolution at all and userspace has to tell it
via S_FMT.
2) The hardware can parse the initial resolution, but is not able to handle
mid-stream resolution changes.
3) The hardware can parse the initial resolution and all following mid-stream
resolution changes.
We can consider 2 the default situation.
In case of 1 the SOURCE_CHANGE event is absent and userspace cannot subscribe
to it. Question: do we want to flag this with the format as well? I.e. with a
V4L2_FMT_FLAG_MANUAL_RESOLUTION? I think just not implementing the SOURCE_CHANGE
event (and documenting this) is sufficient.
In case of 3 the format sets the V4L2_FMT_FLAG_DYN_RESOLUTION flag.
What do you think?
Regards,
Hans
>
> Regards,
>
> Hans
>
>> This flag is mainly aimed at stateful decoder drivers.
>>
>> This RFC is motivated by my development on the amlogic video decoder
>> driver, which does not support dynamic resolution switching for older
>> coded formats (MPEG 1/2, MPEG 4 part II, H263). It does however support
>> it for the newer formats (H264, HEVC, VP9).
>>
>> The specification regarding stateful video decoders should be amended
>> to include that, in the absence of this flag for a certain format,
>> userspace is expected to extract the coded resolution and allocate
>> a sufficient amount of capture buffers on its own.
>> I understand that this point may be tricky, since older kernels with
>> close-to-spec drivers would not have this flag available, yet would
>> fully support dynamic resolution switching.
>> However, with the spec not merged in yet, I wanted to have your opinion
>> on this late addition.
>>
>> The RFC patches also adds support for this flag for the 4 following
>> stateful decoder drivers:
>> - venus
>> - s5p-mfc
>> - mtk-vcodec
>> - vicodec
>>
>> Maxime Jourdan (5):
>> media: videodev2: add V4L2_FMT_FLAG_DYN_RESOLUTION
>> media: venus: vdec: flag OUTPUT formats with
>> V4L2_FMT_FLAG_DYN_RESOLUTION
>> media: s5p_mfc_dec: flag OUTPUT formats with
>> V4L2_FMT_FLAG_DYN_RESOLUTION
>> media: mtk-vcodec: flag OUTPUT formats with
>> V4L2_FMT_FLAG_DYN_RESOLUTION
>> media: vicodec: flag vdec/stateful OUTPUT formats with
>> V4L2_FMT_FLAG_DYN_RESOLUTION
>>
>> Documentation/media/uapi/v4l/vidioc-enum-fmt.rst | 7 +++++++
>> drivers/media/platform/mtk-vcodec/mtk_vcodec_dec.c | 4 ++++
>> drivers/media/platform/mtk-vcodec/mtk_vcodec_drv.h | 1 +
>> drivers/media/platform/qcom/venus/core.h | 1 +
>> drivers/media/platform/qcom/venus/vdec.c | 11 +++++++++++
>> drivers/media/platform/s5p-mfc/s5p_mfc_common.h | 1 +
>> drivers/media/platform/s5p-mfc/s5p_mfc_dec.c | 13 +++++++++++++
>> drivers/media/platform/vicodec/vicodec-core.c | 2 ++
>> include/uapi/linux/videodev2.h | 5 +++--
>> 9 files changed, 43 insertions(+), 2 deletions(-)
>>
>
