Re: [PATCH v4 2/2] media: iris: add support for vbv delay

[Sachin Kumar Garg <sachin.garg@oss.qualcomm.com>]

On 9/27/2026 11:55 PM, Dmitry Baryshkov wrote:
> On Sun, Sep 27, 2026 at 09:27:46AM +0530, Sachin Kumar Garg wrote:
>> Add the VBV_DELAY instance capability for the HFI Gen2 encoder,
>> exposed to userspace via V4L2_CID_MPEG_VIDEO_VBV_DELAY and mapped to
>> HFI_PROP_VBV_DELAY through a new iris_set_vbv_delay(). The property
>> is only meaningful for CBR rate-control modes.
>>
>> Low VBV delay values (34-100 ms) require the encoder to run
>> with a single video pipe, so extend iris_set_pipe() to force
>> work_route to 1 whenever the configured VBV_DELAY falls in that
>> range.
>>
>> Reviewed-by: Vikash Garodia <vikash.garodia@oss.qualcomm.com>
>> Signed-off-by: Sachin Kumar Garg <sachin.garg@oss.qualcomm.com>
>> ---
>>   drivers/media/platform/qcom/iris/iris_ctrls.c      | 37 +++++++++++++++++++++-
>>   drivers/media/platform/qcom/iris/iris_ctrls.h      |  1 +
>>   drivers/media/platform/qcom/iris/iris_hfi_gen2.c   | 12 ++++++-
>>   .../platform/qcom/iris/iris_hfi_gen2_defines.h     |  1 +
>>   .../platform/qcom/iris/iris_platform_common.h      |  1 +
>>   5 files changed, 50 insertions(+), 2 deletions(-)
>>
>> @@ -541,8 +545,19 @@ int iris_set_stage(struct iris_inst *inst, enum platform_inst_fw_cap_type cap_id
>>   int iris_set_pipe(struct iris_inst *inst, enum platform_inst_fw_cap_type cap_id)
>>   {
>>   	const struct iris_hfi_session_ops *hfi_ops = inst->hfi_session_ops;
>> -	u32 work_route = inst->fw_caps[PIPE].value;
>> +	u32 work_route = inst->fw_caps[PIPE].max;
> 
> Why is being set to the max value instead of using the .value?
> 

fw_caps[PIPE].min/.max/.value are all seeded from the same platform 
constant (num_vpp_pipe) at init, so .max and .value were interchangeable 
before this patch. This patch now writes the applied pipe count back 
into .value (used elsewhere for power/cycle estimation), which makes 
.value stateful. Since iris_set_pipe() is re-invoked on every resolution 
change while streaming, seeding work_route from .value would let a 
previous single-pipe override persist as the new baseline on the next 
call, even after the VBV-delay/CBR condition no longer applies. Reading 
from .max instead keeps the default pipe count stable and re-evaluates 
the workaround fresh on every call.

Regards,
Sachin>>   	u32 hfi_id = inst->fw_caps[cap_id].hfi_id;
>> +	u32 vbv_delay;
>> +
>> +	if (inst->domain == ENCODER &&
>> +	    inst->fw_caps[FRAME_RC_ENABLE].value &&
>> +	    inst->fw_caps[BITRATE_MODE].value == V4L2_MPEG_VIDEO_BITRATE_MODE_CBR) {
>> +		vbv_delay = inst->fw_caps[VBV_DELAY].value;
>> +		if (vbv_delay >= 34 && vbv_delay <= 100)
>> +			work_route = 1;
>> +	}
>> +
>> +	inst->fw_caps[PIPE].value = work_route;
>>   
>>   	return hfi_ops->session_set_property(inst, hfi_id,
>>   					     HFI_HOST_FLAGS_NONE,