linux-kernel - Re: [PATCH v2] media: venus: add support for key frame

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Date:   Thu, 25 Oct 2018 16:30:58 +0900
From:   Tomasz Figa <tfiga@...omium.org>
To:     vgarodia@...eaurora.org
Cc:     mgottam@...eaurora.org,
        Stanimir Varbanov <stanimir.varbanov@...aro.org>,
        Hans Verkuil <hverkuil@...all.nl>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Alexandre Courbot <acourbot@...omium.org>,
        linux-media-owner@...r.kernel.org
Subject: Re: [PATCH v2] media: venus: add support for key frame

On Thu, Oct 25, 2018 at 4:23 PM Vikash Garodia <vgarodia@...eaurora.org> wrote:
>
> On 2018-10-24 20:02, Tomasz Figa wrote:
> > On Wed, Oct 24, 2018 at 10:52 PM Malathi Gottam
> > <mgottam@...eaurora.org> wrote:
> >>
> >> When client requests for a keyframe, set the property
> >> to hardware to generate the sync frame.
> >>
> >> Signed-off-by: Malathi Gottam <mgottam@...eaurora.org>
> >> ---
> >>  drivers/media/platform/qcom/venus/venc_ctrls.c | 16 +++++++++++++++-
> >>  1 file changed, 15 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/media/platform/qcom/venus/venc_ctrls.c
> >> b/drivers/media/platform/qcom/venus/venc_ctrls.c
> >> index 45910172..6c2655d 100644
> >> --- a/drivers/media/platform/qcom/venus/venc_ctrls.c
> >> +++ b/drivers/media/platform/qcom/venus/venc_ctrls.c
> >> @@ -79,8 +79,10 @@ static int venc_op_s_ctrl(struct v4l2_ctrl *ctrl)
> >>  {
> >>         struct venus_inst *inst = ctrl_to_inst(ctrl);
> >>         struct venc_controls *ctr = &inst->controls.enc;
> >> +       struct hfi_enable en = { .enable = 1 };
> >>         u32 bframes;
> >>         int ret;
> >> +       u32 ptype;
> >>
> >>         switch (ctrl->id) {
> >>         case V4L2_CID_MPEG_VIDEO_BITRATE_MODE:
> >> @@ -173,6 +175,15 @@ static int venc_op_s_ctrl(struct v4l2_ctrl *ctrl)
> >>
> >>                 ctr->num_b_frames = bframes;
> >>                 break;
> >> +       case V4L2_CID_MPEG_VIDEO_FORCE_KEY_FRAME:
> >> +               if (inst->streamon_out && inst->streamon_cap) {
> >> +                       ptype =
> >> HFI_PROPERTY_CONFIG_VENC_REQUEST_SYNC_FRAME;
> >> +                       ret = hfi_session_set_property(inst, ptype,
> >> &en);
> >> +
> >> +                       if (ret)
> >> +                               return ret;
> >> +               }
> >> +               break;
> >
> > This is still not the right way to handle this.
> >
> > Please see the documentation of this control [1]:
> >
> > "V4L2_CID_MPEG_VIDEO_FORCE_KEY_FRAME (button)
> > Force a key frame for the next queued buffer. Applicable to encoders.
> > This is a general, codec-agnostic keyframe control."
> >
> > Even if the driver is not streaming, it must remember that the
> > keyframe was requested for next buffer. The next time userspace QBUFs
> > an OUTPUT buffer, it should ask the hardware to encode that OUTPUT
> > buffer into a keyframe.
>
> That's correct. Driver can cache the client request and set it when the
> hardware
> is capable of accepting the property.
> Still the issue having the requested OUTPUT buffer to be encoded as sync
> frame will
> be there. If there are few frames queued before streamon, driver will
> only keep a
> note that it has to set the request for keyframe, but not the exact one
> which was
> requested.

The description (quoted above) specifies exactly that the control
applies only to the next queued buffer. It's a "button" control, so
when the application sets it (to 1), it triggers a call to driver's
s_ctrl callback and then resets to 0 automatically.

>
> > [1]
> > https://www.kernel.org/doc/html/latest/media/uapi/v4l/extended-controls.html?highlight=v4l2_cid_mpeg_video_force_key_frame
> >
> > But generally, the proper modern way for the userspace to request a
> > keyframe is to set the V4L2_BUF_FLAG_KEYFRAME flag in the
> > vb2_buffer_flag when queuing an OUTPUT buffer. It's the only
> > guaranteed way to ensure that the keyframe will be encoded exactly for
> > the selected frame. (The V4L2 control API doesn't guarantee any
> > synchronization between controls and buffers itself.)
>
> This is a better way to handle it to ensure exact buffer gets encoded as
> sync frame.

It was created later to solve this problem. For compatibility, we have
to keep supporting the control too.

Best regards,
Tomasz