libcamera: delayed_controls: Add notion of priority write

If an exposure time change adjusts the vblanking limits, and we set both
VBLANK and EXPOSURE controls through the VIDIOC_S_EXT_CTRLS ioctl, the
latter may fail if the value is outside of the limits calculated by the
old VBLANK value. This is a limitation in V4L2 and cannot be fixed by
setting VBLANK before EXPOSURE in a single VIDIOC_S_EXT_CTRLS ioctl.

The workaround here is to have the DelayedControls object mark the
VBLANK control as "priority write", which then write VBLANK separately
from (and ahead of) any other controls. This way, the sensor driver will
update the EXPOSURE control with new limits before the new values is
presented, and will thus be seen as valid.

To support this, a new struct DelayedControls::ControlParams is used in
the constructor to provide the control delay value as well as the
priority write flag.

Signed-off-by: Naushir Patuck <naush@raspberrypi.com>
Tested-by: David Plowman <david.plowman@raspberrypi.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Tested-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
[Kieran: Fix up trivial comments, merge conflicts]
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

1 files changed, 7 insertions, 2 deletions

diff --git a/include/libcamera/internal/delayed_controls.h b/include/libcamera/internal/delayed_controls.h
index dc447a88..564d9f2e 100644
--- a/include/libcamera/internal/delayed_controls.h
+++ b/include/libcamera/internal/delayed_controls.h
@@ -19,8 +19,13 @@ class V4L2Device;
 class DelayedControls
 {
 public:
+	struct ControlParams {
+		unsigned int delay;
+		bool priorityWrite;
+	};
+
 	DelayedControls(V4L2Device *device,
-			const std::unordered_map<uint32_t, unsigned int> &delays);
+			const std::unordered_map<uint32_t, ControlParams> &controlParams);
 
 	void reset();
 
@@ -64,7 +69,7 @@ private:
 
 	V4L2Device *device_;
 	/* \todo Evaluate if we should index on ControlId * or unsigned int */
-	std::unordered_map<const ControlId *, unsigned int> delays_;
+	std::unordered_map<const ControlId *, ControlParams> controlParams_;
 	unsigned int maxDelay_;
 
 	bool running_;