[PATCH v2 0/2] media: iris: add vbv delay support

[Sachin Kumar Garg]

This series adds VBV_DELAY (V4L2_CID_MPEG_VIDEO_VBV_DELAY) support
for Qualcomm iris encoder sessions, allowing users to configure the
initial VBV (Video Buffer Verifier) delay for CBR-encoded streams.
This is useful for latency-sensitive encoding use cases (e.g.
low-latency streaming) where the client needs explicit control over
the encoder's buffering delay.

Patch 1 is a prerequisite for patch 2. The PIPE capability (control
over the number of VPP hardware pipes used for a session) was
previously only wired up for decoder sessions. Achieving low VBV delay
values (34-100 ms) requires the encoder to be constrained to a single
VPP pipe, so patch 1 enables the PIPE capability on the encoder path as
well, which patch 2 then relies on to force single-pipe operation when
VBV delay falls in that low-latency range.

Patch 2 adds the VBV_DELAY capability: it registers HFI_PROP_VBV_DELAY,
wires up the V4L2_CID_MPEG_VIDEO_VBV_DELAY control for the gen2
encoder, and only applies the property when rate control is set to CBR
since VBV delay is only meaningful for constant-bitrate encoding.
It adds vbv_delay support for iris HFI Gen2 based targets (qcs8300,
sm8550, sm8650, sm8750, x1p42100). Support for HFI Gen1 targets will
be added in a follow-up series.

This series has been verified with GST level testing.
Command used:
gst-launch-1.0 -v videotestsrc ! video/x-raw,format=NV12, \
width=1280,height=720,framerate=30/1 ! v4l2h264enc output-io-mode=4 \
capture-io-mode=4 extra-controls="controls,video_bitrate_mode=1, \
initial_delay_for_vbv_control=300;" ! filesink location=/opt/test_enc.h264

Signed-off-by: Sachin Kumar Garg <sachin.garg@xxxxxxxxxxxxxxxx>
---
Changes in v2:
- iris_set_pipe(): use inclusive VBV_DELAY bounds (>= 34 && <= 100 ms)
  matching the documented range.
- iris_set_pipe(): only force single-pipe under CBR rate control so
  a stale in-range VBV_DELAY no longer affects non-CBR streams.
- iris_set_pipe(): read fw_caps[VBV_DELAY].value once instead of
  twice in the same condition, and derive the default work_route from
  the immutable fw_caps[PIPE].max instead of the self-mutated .value,
  writing the final decision back into .value so frequency scaling
  picks up the corrected pipe count instead of a stale one.
- iris_set_vbv_delay(): drop the dev_err() logged for non-CBR rate
  control; that is an expected, valid configuration, not an error.
- Link to v1: https://lore.kernel.org/r/20260730-iris_vbv_delay-v1-0-7b5a7953bcdf@xxxxxxxxxxxxxxxx

---
Sachin Kumar Garg (2):
      media: iris: enable pipe for hfi gen2 encoder
      media: iris: add support for vbv delay

 drivers/media/platform/qcom/iris/iris_ctrls.c      | 52 ++++++++++++++++++++--
 drivers/media/platform/qcom/iris/iris_ctrls.h      |  1 +
 drivers/media/platform/qcom/iris/iris_hfi_gen2.c   | 19 +++++++-
 .../platform/qcom/iris/iris_hfi_gen2_defines.h     |  1 +
 .../platform/qcom/iris/iris_platform_common.h      |  1 +
 5 files changed, 69 insertions(+), 5 deletions(-)
---
base-commit: a52e6f7923c17a672135b485ffd96fbd72f46267
change-id: 20260730-iris_vbv_delay-343d2fa30842

Best regards,
-- 
Sachin Kumar Garg <sachin.garg@xxxxxxxxxxxxxxxx>