[libcamera-devel] [PATCH v3 23/30] cam: drm: Support per-plane stride values

[Laurent Pinchart]

The stride is not always identical for all planes for multi-planar
formats. Semi-planar YUV formats without horizontal subsampling often
have a chroma stride equal to twice the luma stride, and tri-planar YUV
formats with a 1/2 horizontal subsampling often have a chroma stride
equal to half the luma stride. This isn't correctly taken into account
when creating a DRM frame buffer, as the same stride is set for all
planes.

libcamera doesn't report per-plane stride values yet, but uses chroma
strides that match the above description for all currently supported
platforms. Calculation the chrome strides appropriately in the KMSSink
class, and pass them to DRM::createFrameBuffer().

Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
Reviewed-by: Jean-Michel Hautbois <jeanmichel.hautbois at ideasonboard.com>
---
 src/cam/drm.cpp      |  7 +++----
 src/cam/drm.h        |  5 ++++-
 src/cam/kms_sink.cpp | 28 +++++++++++++++++++++++++++-
 3 files changed, 34 insertions(+), 6 deletions(-)

diff --git a/src/cam/drm.cpp b/src/cam/drm.cpp
index da317e27cb19..ac47b8bd3287 100644
--- a/src/cam/drm.cpp
+++ b/src/cam/drm.cpp
@@ -595,12 +595,12 @@ const Object *Device::object(uint32_t id)
 std::unique_ptr<FrameBuffer> Device::createFrameBuffer(
 	const libcamera::FrameBuffer &buffer,
 	const libcamera::PixelFormat &format,
-	const libcamera::Size &size, unsigned int stride)
+	const libcamera::Size &size,
+	const std::array<uint32_t, 4> &strides)
 {
 	std::unique_ptr<FrameBuffer> fb{ new FrameBuffer(this) };
 
 	uint32_t handles[4] = {};
-	uint32_t pitches[4] = {};
 	uint32_t offsets[4] = {};
 	int ret;
 
@@ -623,13 +623,12 @@ std::unique_ptr<FrameBuffer> Device::createFrameBuffer(
 		fb->planes_.push_back({ handle });
 
 		handles[i] = handle;
-		pitches[i] = stride;
 		offsets[i] = 0; /* TODO */
 		++i;
 	}
 
 	ret = drmModeAddFB2(fd_, size.width, size.height, format.fourcc(), handles,
-			    pitches, offsets, &fb->id_, 0);
+			    strides.data(), offsets, &fb->id_, 0);
 	if (ret < 0) {
 		ret = -errno;
 		std::cerr
diff --git a/src/cam/drm.h b/src/cam/drm.h
index ee2304025208..00f7e798b771 100644
--- a/src/cam/drm.h
+++ b/src/cam/drm.h
@@ -7,9 +7,11 @@
 #ifndef __CAM_DRM_H__
 #define __CAM_DRM_H__
 
+#include <array>
 #include <list>
 #include <map>
 #include <memory>
+#include <stdint.h>
 #include <string>
 #include <vector>
 
@@ -298,7 +300,8 @@ public:
 	std::unique_ptr<FrameBuffer> createFrameBuffer(
 		const libcamera::FrameBuffer &buffer,
 		const libcamera::PixelFormat &format,
-		const libcamera::Size &size, unsigned int stride);
+		const libcamera::Size &size,
+		const std::array<uint32_t, 4> &strides);
 
 	libcamera::Signal<AtomicRequest *> requestComplete;
 
diff --git a/src/cam/kms_sink.cpp b/src/cam/kms_sink.cpp
index 8c0b79c63922..658192efc105 100644
--- a/src/cam/kms_sink.cpp
+++ b/src/cam/kms_sink.cpp
@@ -7,10 +7,12 @@
 
 #include "kms_sink.h"
 
+#include <array>
 #include <algorithm>
 #include <assert.h>
 #include <iostream>
 #include <memory>
+#include <stdint.h>
 #include <string.h>
 
 #include <libcamera/camera.h>
@@ -65,8 +67,32 @@ KMSSink::KMSSink(const std::string &connectorName)
 
 void KMSSink::mapBuffer(libcamera::FrameBuffer *buffer)
 {
+	std::array<uint32_t, 4> strides = {};
+
+	/* \todo Should libcamera report per-plane strides ? */
+	unsigned int uvStrideMultiplier;
+
+	switch (format_) {
+	case libcamera::formats::NV24:
+	case libcamera::formats::NV42:
+		uvStrideMultiplier = 4;
+		break;
+	case libcamera::formats::YUV420:
+	case libcamera::formats::YVU420:
+	case libcamera::formats::YUV422:
+		uvStrideMultiplier = 1;
+		break;
+	default:
+		uvStrideMultiplier = 2;
+		break;
+	}
+
+	strides[0] = stride_;
+	for (unsigned int i = 1; i < buffer->planes().size(); ++i)
+		strides[i] = stride_ * uvStrideMultiplier / 2;
+
 	std::unique_ptr<DRM::FrameBuffer> drmBuffer =
-		dev_.createFrameBuffer(*buffer, format_, size_, stride_);
+		dev_.createFrameBuffer(*buffer, format_, size_, strides);
 	if (!drmBuffer)
 		return;
 
-- 
Regards,

Laurent Pinchart