[PATCH v3 4/4] libcamera: pipeline: uvcvideo: Fix `ExposureTime` control handling

[Barnabás Pőcze]

Hi

2025. 03. 21. 15:17 keltezéssel, Jacopo Mondi írta:
> Hi Barnabás
> 
> On Fri, Mar 14, 2025 at 06:42:48PM +0100, Barnabás Pőcze wrote:
>> The documentation of `ExposureTime` states that its value is ignored if
>> `ExposureTimeMode` is not manual. This is currently not handled, and if
>> `ExposureTimeMode` is automatic and `ExposureTime` is set, then the
>> controls will be rejected, as expected.
>>
>> Only try to set `V4L2_CID_EXPOSURE_ABSOLUTE` if the current exposure mode
>> is manual. To be able to handle requests that set both `ExposureTime{,Mode}`,
>> process `ExposureTimeMode` first directly in `processControls()`, and store
>> this new mode in a temporary location. Then have `processControl()` act on
>> this temporary state, and only persist the temporary state if `setControls()`
>> on the video device succeeds.
>>
>> Bug: https://bugs.libcamera.org/show_bug.cgi?id=242
>> Signed-off-by: Barnabás Pőcze <barnabas.pocze at ideasonboard.com>
>> ---
>>   src/libcamera/pipeline/uvcvideo/uvcvideo.cpp | 52 ++++++++++++--------
>>   1 file changed, 31 insertions(+), 21 deletions(-)
>>
>> diff --git a/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp b/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
>> index 7d882ebe1..22d286e49 100644
>> --- a/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
>> +++ b/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
>> @@ -108,7 +108,7 @@ public:
>>   	bool match(DeviceEnumerator *enumerator) override;
>>
>>   private:
>> -	int processControl(const UVCCameraData *data, ControlList *controls,
>> +	int processControl(const UVCCameraData::State &state, ControlList *controls,
>>   			   unsigned int id, const ControlValue &value);
>>   	int processControls(UVCCameraData *data, Request *request);
>>
>> @@ -333,7 +333,7 @@ void PipelineHandlerUVC::stopDevice(Camera *camera)
>>   	data->state_.reset();
>>   }
>>
>> -int PipelineHandlerUVC::processControl(const UVCCameraData *data, ControlList *controls,
>> +int PipelineHandlerUVC::processControl(const UVCCameraData::State &state, ControlList *controls,
>>   				       unsigned int id, const ControlValue &value)
>>   {
>>   	uint32_t cid;
>> @@ -378,26 +378,13 @@ int PipelineHandlerUVC::processControl(const UVCCameraData *data, ControlList *c
>>   	}
>>
>>   	case V4L2_CID_EXPOSURE_AUTO: {
>> -		std::optional<v4l2_exposure_auto_type> mode;
>> -
>> -		switch (value.get<int32_t>()) {
>> -		case controls::ExposureTimeModeAuto:
>> -			mode = data->autoExposureMode_;
>> -			break;
>> -		case controls::ExposureTimeModeManual:
>> -			mode = data->manualExposureMode_;
>> -			break;
>> -		}
>> -
>> -		if (!mode)
>> -			return -EINVAL;
>> -
>> -		controls->set(V4L2_CID_EXPOSURE_AUTO, static_cast<int32_t>(*mode));
>> +		/* Handled directly in `processControls()`. */
>>   		break;
>>   	}
>>
>>   	case V4L2_CID_EXPOSURE_ABSOLUTE:
>> -		controls->set(cid, value.get<int32_t>() / 100);
>> +		if (state.exp == controls::ExposureTimeModeManual)
>> +			controls->set(cid, value.get<int32_t>() / 100);
>>   		break;
>>
>>   	case V4L2_CID_CONTRAST:
>> @@ -428,9 +415,30 @@ int PipelineHandlerUVC::processControl(const UVCCameraData *data, ControlList *c
>>   int PipelineHandlerUVC::processControls(UVCCameraData *data, Request *request)
>>   {
>>   	ControlList controls(data->video_->controls());
>> +	const auto &reqControls = request->controls();
>> +	auto newState = data->state_;
>> +
>> +	if (const auto exp = reqControls.get(controls::ExposureTimeMode)) {
>> +		std::optional<v4l2_exposure_auto_type> mode;
>>
>> -	for (const auto &[id, value] : request->controls())
>> -		processControl(data, &controls, id, value);
>> +		switch (*exp) {
>> +		case controls::ExposureTimeModeAuto:
>> +			mode = data->autoExposureMode_;
>> +			break;
>> +		case controls::ExposureTimeModeManual:
>> +			mode = data->manualExposureMode_;
>> +			break;
>> +		}
>> +
>> +		if (!mode)
>> +			return -EINVAL;
>> +
>> +		controls.set(V4L2_CID_EXPOSURE_AUTO, static_cast<int32_t>(*mode));
>> +		newState.exp = static_cast<controls::ExposureTimeModeEnum>(*exp);
> 
> Can't you just update data->state before calling processControl to
> avoid passing newState to that function ?

If the controls cannot be set, then I think the state should not be changed, this
is why it operates on a copy, which is only persisted after `setControls()` succeeds.


Regards,
Barnabás Pőcze

> 
>> +	}
>> +
>> +	for (const auto &[id, value] : reqControls)
>> +		processControl(newState, &controls, id, value);
>>
>>   	for (const auto &ctrl : controls)
>>   		LOG(UVC, Debug)
>> @@ -443,7 +451,9 @@ int PipelineHandlerUVC::processControls(UVCCameraData *data, Request *request)
>>   		return ret < 0 ? ret : -EINVAL;
>>   	}
>>
>> -	return ret;
>> +	data->state_ = newState;
>> +
>> +	return 0;
>>   }
>>
>>   int PipelineHandlerUVC::queueRequestDevice(Camera *camera, Request *request)
>> --
>> 2.48.1
>>