android: capabilities: Cap frame rate to 30 FPS

Limit the reported minumum frame duration to 30 FPS.

The reason to do is to bring the libcamra HAL in par with the Intel
HAL implementation on IPU3 platform, where 30FPS is the frame rate used
to perform quality tuning in the closed-source IPA module and has been
validated as the most efficient rate for the power/performace budget.

This change bring into the HAL a platform specific constraints, which
might be opportune for most platforms but should rather be configurable
by system integrators. Record that with a \todo entry.

Also record that, even if we report a lower frame rate, we currently
do not limit what the camera actually produce.

Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/src/android/camera_capabilities.cpp b/src/android/camera_capabilities.cpp
index f2f984c5..f357902e 100644
--- a/src/android/camera_capabilities.cpp
+++ b/src/android/camera_capabilities.cpp
@@ -646,6 +646,30 @@ int CameraCapabilities::initializeStreamConfigurations()
 
 			int64_t minFrameDuration = frameDurations->second.min().get<int64_t>() * 1000;
 			int64_t maxFrameDuration = frameDurations->second.max().get<int64_t>() * 1000;
+
+			/*
+			 * Cap min frame duration to 30 FPS.
+			 *
+			 * 30 frames per second has been validated as the most
+			 * opportune frame rate for quality tuning, and power
+			 * vs performances budget on Intel IPU3-based
+			 * Chromebooks.
+			 *
+			 * \todo This is a platform-specific decision that needs
+			 * to be abstracted and delegated to the configuration
+			 * file.
+			 *
+			 * \todo libcamera only allows to control frame duration
+			 * through the per-request controls::FrameDuration
+			 * control. If we cap the durations here, we should be
+			 * capable of configuring the camera to operate at such
+			 * duration without requiring to have the FrameDuration
+			 * control to be specified for each Request. Defer this
+			 * to the in-development configuration API rework.
+			 */
+			if (minFrameDuration < 1e9 / 30.0)
+				minFrameDuration = 1e9 / 30.0;
+
 			streamConfigurations_.push_back({
 				res, androidFormat, minFrameDuration, maxFrameDuration,
 			});