[libcamera-devel] [PATCH v5] cam: kms_sink: Remove limitation that camera and display must match

[Eric Curtin]

There is a limitation that requires input and output to be pixel
for pixel identical in terms of height and width. Remove this
limitation to enable more hardware that doesn't match. Just start
drawing from top left 0, 0 corner. Try and pick the mode closest to the
stream size.

Suggested-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
Signed-off-by: Eric Curtin <ecurtin at redhat.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
Tested-by: Eric Curtin <ecurtin at redhat.com>
---
Changes in v5:
- Tested Laurents suggested change successfully
- Added to commit message about trying to pick closest

Changes in v4:
- Change commit message to say top left
- Spaces to tabs

Changes in v3:
- Much simplified version of the patch where we just attempt to
  draw from point 0, 0. Only in the case where we do not find a
  matching mode. Can expand to do centralization, scaling, etc.
  in further patches if needs be.

Changes in v2:
- Tested and support drawing from negative pixel range
  kernel parameter (video=960x540 at 60) was useful here
---
 src/cam/kms_sink.cpp | 45 +++++++++++++++++++++++++++++++++++---------
 1 file changed, 36 insertions(+), 9 deletions(-)

diff --git a/src/cam/kms_sink.cpp b/src/cam/kms_sink.cpp
index 7add81a6..7904bca8 100644
--- a/src/cam/kms_sink.cpp
+++ b/src/cam/kms_sink.cpp
@@ -11,6 +11,7 @@
 #include <algorithm>
 #include <assert.h>
 #include <iostream>
+#include <limits.h>
 #include <memory>
 #include <stdint.h>
 #include <string.h>
@@ -112,6 +113,7 @@ int KMSSink::configure(const libcamera::CameraConfiguration &config)
 
 	const libcamera::StreamConfiguration &cfg = config.at(0);
 
+	/* Find the best mode for the stream size. */
 	const std::vector<DRM::Mode> &modes = connector_->modes();
 	const auto iter = std::find_if(modes.begin(), modes.end(),
 				       [&](const DRM::Mode &mode) {
@@ -120,6 +122,32 @@ int KMSSink::configure(const libcamera::CameraConfiguration &config)
 				       });
 	if (iter == modes.end()) {
 		std::cerr << "No mode matching " << cfg.size << std::endl;
+
+		unsigned int cfgArea = cfg.size.width * cfg.size.height;
+		unsigned int bestDistance = UINT_MAX;
+
+		for (const DRM::Mode &mode : modes) {
+			unsigned int modeArea = mode.hdisplay * mode.vdisplay;
+			unsigned int distance = modeArea > cfgArea
+							? modeArea - cfgArea
+							: cfgArea - modeArea;
+
+			if (distance < bestDistance) {
+				mode_ = &mode;
+				bestDistance = distance;
+
+				/*
+				 * If the sizes match exactly, there will be no better
+				 * match.
+				 */
+				if (distance == 0)
+					break;
+			}
+		}
+	}
+
+	if (!mode_) {
+		std::cerr << "No modes\n";
 		return -EINVAL;
 	}
 
@@ -127,7 +155,6 @@ int KMSSink::configure(const libcamera::CameraConfiguration &config)
 	if (ret < 0)
 		return ret;
 
-	mode_ = &*iter;
 	size_ = cfg.size;
 	stride_ = cfg.stride;
 
@@ -199,10 +226,10 @@ int KMSSink::configurePipeline(const libcamera::PixelFormat &format)
 		return ret;
 	}
 
-	std::cout
-		<< "Using KMS plane " << plane_->id() << ", CRTC " << crtc_->id()
-		<< ", connector " << connector_->name()
-		<< " (" << connector_->id() << ")" << std::endl;
+	std::cout << "Using KMS plane " << plane_->id() << ", CRTC "
+		  << crtc_->id() << ", connector " << connector_->name() << " ("
+		  << connector_->id() << "), mode " << mode_->hdisplay << "x"
+		  << mode_->vdisplay << "@" << mode_->vrefresh << std::endl;
 
 	return 0;
 }
@@ -295,12 +322,12 @@ bool KMSSink::processRequest(libcamera::Request *camRequest)
 		drmRequest->addProperty(plane_, "CRTC_ID", crtc_->id());
 		drmRequest->addProperty(plane_, "SRC_X", 0 << 16);
 		drmRequest->addProperty(plane_, "SRC_Y", 0 << 16);
-		drmRequest->addProperty(plane_, "SRC_W", mode_->hdisplay << 16);
-		drmRequest->addProperty(plane_, "SRC_H", mode_->vdisplay << 16);
+		drmRequest->addProperty(plane_, "SRC_W", size_.width << 16);
+		drmRequest->addProperty(plane_, "SRC_H", size_.height << 16);
 		drmRequest->addProperty(plane_, "CRTC_X", 0);
 		drmRequest->addProperty(plane_, "CRTC_Y", 0);
-		drmRequest->addProperty(plane_, "CRTC_W", mode_->hdisplay);
-		drmRequest->addProperty(plane_, "CRTC_H", mode_->vdisplay);
+		drmRequest->addProperty(plane_, "CRTC_W", size_.width);
+		drmRequest->addProperty(plane_, "CRTC_H", size_.height);
 
 		flags |= DRM::AtomicRequest::FlagAllowModeset;
 	}
-- 
2.35.3