[PATCH v2 1/2] libcamera: pipeline: uvcvideo: Fix `ExposureTimeMode` control setup

[Barnabás Pőcze]

Hi


2025. február 28., péntek 12:06 keltezéssel, Jacopo Mondi <jacopo.mondi at ideasonboard.com> írta:

> Hi Barnabás
> 
> On Mon, Feb 17, 2025 at 06:53:34PM +0000, Barnabás Pőcze wrote:
> > `ControlInfo(Span<const int32_t>{...})` calls the incorrect constructor
> > of `ControlInfo`. The intended constructor to be called is
> > `ControlInfo(Span<const ControlValue>, ...)` however that is not called
> > because a span of `const int32_t` is passed. Instead, the constructor
> > `ControlInfo(const ControlValue &min, const ControlValue &max, ...)`
> > will be called.
> >
> > Furthermore, since `values.back()` is used, only the last element of
> > the array is actually populated.
> >
> > To fix this, convert the array to contain `ControlValue` objects
> > and use a separate variable to keep track of which element is to
> > be populated next.
> >
> > The available modes are saved for later so that the appropriate mode
> > can be selected when the control is set.
> >
> > Fixes: bad8d591f8acfa ("libcamera: uvcvideo: Register ExposureTimeMode control")
> > Signed-off-by: Barnabás Pőcze <pobrn at protonmail.com>
> > ---
> >  src/libcamera/pipeline/uvcvideo/uvcvideo.cpp | 46 ++++++++++++--------
> >  1 file changed, 27 insertions(+), 19 deletions(-)
> >
> > diff --git a/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp b/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
> > index dedcac89b..1f604b91e 100644
> > --- a/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
> > +++ b/src/libcamera/pipeline/uvcvideo/uvcvideo.cpp
> > @@ -6,6 +6,7 @@
> >   */
> >
> >  #include <algorithm>
> > +#include <bitset>
> >  #include <cmath>
> >  #include <fstream>
> >  #include <map>
> > @@ -58,6 +59,13 @@ public:
> >  	Stream stream_;
> >  	std::map<PixelFormat, std::vector<SizeRange>> formats_;
> >
> > +	std::bitset<
> > +		std::max(V4L2_EXPOSURE_AUTO,
> > +		std::max(V4L2_EXPOSURE_MANUAL,
> > +		std::max(V4L2_EXPOSURE_APERTURE_PRIORITY,
> > +			 V4L2_EXPOSURE_SHUTTER_PRIORITY))) + 1
> 
> The enum v4l2_exposure_auto_type definition is part of the linux
> kernel ABI, and I don't expect them to change. Maybe new modes might
> be added, but in that case you would have to change the above anyway.

I think the intent here is very clear. Alternatives I can think of: `std::bitset<4>`,
or `std::bitset<V4L2_EXPOSURE_APERTURE_PRIORITY + 1>` are all less clear in my opinion.

If there was a `V4L2_EXPOSURE_LAST` or `V4L2_EXPOSURE_COUNT` or whatever, I would
have used that, but it doesn't appear to be a thing.

`std::set<v4l2_exposure_auto_type>` is an option, but I would avoid it if possible,
however maybe that will be it...

Any suggestions?


> 
> 
> > +	> availableExposureModes_;
> > +
> >  private:
> >  	bool generateId();
> >
> > @@ -725,25 +733,25 @@ void UVCCameraData::addControl(uint32_t cid, const ControlInfo &v4l2Info,
> >  		 * ExposureTimeModeManual = { V4L2_EXPOSURE_MANUAL,
> >  		 *			      V4L2_EXPOSURE_SHUTTER_PRIORITY }
> >  		 */
> > -		std::array<int32_t, 2> values{};
> > -
> > -		auto it = std::find_if(v4l2Values.begin(), v4l2Values.end(),
> > -			[&](const ControlValue &val) {
> > -				return (val.get<int32_t>() == V4L2_EXPOSURE_APERTURE_PRIORITY ||
> > -					val.get<int32_t>() == V4L2_EXPOSURE_AUTO) ? true : false;
> > -			});
> > -		if (it != v4l2Values.end())
> > -			values.back() = static_cast<int32_t>(controls::ExposureTimeModeAuto);
> > -
> > -		it = std::find_if(v4l2Values.begin(), v4l2Values.end(),
> > -			[&](const ControlValue &val) {
> > -				return (val.get<int32_t>() == V4L2_EXPOSURE_SHUTTER_PRIORITY ||
> > -					val.get<int32_t>() == V4L2_EXPOSURE_MANUAL) ? true : false;
> > -			});
> > -		if (it != v4l2Values.end())
> > -			values.back() = static_cast<int32_t>(controls::ExposureTimeModeManual);
> > -
> > -		info = ControlInfo{Span<int32_t>{values}, values[0]};
> > +		for (const ControlValue &value : v4l2Values) {
> > +			auto x = value.get<int32_t>();
> > +			if (0 <= x && static_cast<size_t>(x) < availableExposureModes_.size())
> 
> v4l2Values comes from kernel and can only be a value from enum
> v4l2_exposure_auto_type right ? The above check shouldn't be needed,
> at least the < 0 part..

I suppose you're right, but I still prefer to have bounds checking.


> 
> > +				availableExposureModes_[x] = true;
> > +		}
> > +
> > +		std::array<ControlValue, 2> values;
> > +		std::size_t count = 0;
> > +
> > +		if (availableExposureModes_[V4L2_EXPOSURE_AUTO] || availableExposureModes_[V4L2_EXPOSURE_APERTURE_PRIORITY])
> 
> Break this lines as suggested by Kieran

In my understanding the suggestion was not to break the line. But regardless, I think
I would like to send a slightly different new version (which will not have these
long lines). Since sending this I have come to the conclusion that the
libcamera-control -> v4l2-control mapping should be in a single place.


Regards,
Barnabás Pőcze

> 
> Thanks
>   j
> 
> > +			values[count++] = controls::ExposureTimeModeAuto;
> > +
> > +		if (availableExposureModes_[V4L2_EXPOSURE_MANUAL] || availableExposureModes_[V4L2_EXPOSURE_SHUTTER_PRIORITY])
> > +			values[count++] = controls::ExposureTimeModeManual;
> > +
> > +		if (count == 0)
> > +			return;
> > +
> > +		info = ControlInfo{ Span<const ControlValue>{ values.data(), count }, values[0] };
> >  		break;
> >  	}
> >  	case V4L2_CID_EXPOSURE_ABSOLUTE:
> > --
> > 2.48.1
> >
> >
>