From a5437e1ad12b443b9f173329145490d5c37b2eb8 Mon Sep 17 00:00:00 2001
From: Simon Ser <contact@emersion.fr>
Date: Fri, 12 Feb 2021 18:35:15 +0100
Subject: [PATCH] Display frame via KMS

---
 main.c | 115 ++++++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 109 insertions(+), 6 deletions(-)

diff --git a/main.c b/main.c
index 2a35ba1..18cb5b1 100644
--- a/main.c
+++ b/main.c
@@ -1,3 +1,4 @@
+#include <fcntl.h>
 #include <stdbool.h>
 #include <stdio.h>
 #include <unistd.h>
@@ -8,6 +9,8 @@
 #include <libavutil/hwcontext.h>
 #include <libavutil/hwcontext_drm.h>
 #include <libavutil/pixdesc.h>
+#include <xf86drm.h>
+#include <xf86drmMode.h>
 
 static enum AVPixelFormat hw_pix_fmt = AV_PIX_FMT_NONE;
 
@@ -64,6 +67,44 @@ static enum AVPixelFormat get_hw_format(AVCodecContext *ctx,
 	return AV_PIX_FMT_NONE;
 }
 
+static uint32_t pick_crtc(int drm_fd) {
+	drmModeRes *res = drmModeGetResources(drm_fd);
+	if (!res) {
+		perror("drmModeGetResources");
+		return 0;
+	}
+
+	drmModeConnector *conn = NULL;
+	for (int i = 0; i < res->count_connectors; i++) {
+		drmModeConnector *c = drmModeGetConnector(drm_fd, res->connectors[i]);
+		if (c->connection == DRM_MODE_CONNECTED) {
+			conn = c;
+			break;
+		}
+		drmModeFreeConnector(c);
+	}
+	if (!conn) {
+		fprintf(stderr, "Failed to find connected connector\n");
+		return 0;
+	}
+	if (conn->encoder_id == 0) {
+		fprintf(stderr, "Connector is not connected to an encoder\n");
+		return 0;
+	}
+
+	drmModeFreeResources(res);
+
+	drmModeEncoder *enc = drmModeGetEncoder(drm_fd, conn->encoder_id);
+	if (enc->crtc_id == 0) {
+		fprintf(stderr, "Encoder is not connected to a CRTC\n");
+		return 0;
+	}
+	uint32_t crtc_id = enc->crtc_id;
+	drmModeFreeEncoder(enc);
+
+	return crtc_id;
+}
+
 static int decode_frame(AVFormatContext *input_ctx, int video_stream,
 		AVCodecContext *decoder_ctx, AVFrame **frame_ptr) {
 	int ret;
@@ -137,6 +178,52 @@ static void print_drm_frame_desc(const AVDRMFrameDescriptor *drm_frame_desc) {
 	}
 }
 
+static uint32_t import_drm_frame_desc(const AVDRMFrameDescriptor *drm_frame_desc,
+		int drm_fd, int width, int height) {
+	// VA-API drivers may use separate layers with one plane each, or a single
+	// layer with multiple planes. We need to handle both.
+	uint32_t drm_format = get_drm_frame_format(drm_frame_desc);
+	if (drm_format == DRM_FORMAT_INVALID) {
+		fprintf(stderr, "Failed to get DRM frame format\n");
+		return 0;
+	}
+	fprintf(stderr, "DRM format: 0x%X\n", drm_format);
+
+	uint32_t handles[4];
+	uint32_t pitches[4];
+	uint32_t offsets[4];
+	int k = 0;
+	for (int i = 0; i < drm_frame_desc->nb_layers; i++) {
+		const AVDRMLayerDescriptor *drm_layer = &drm_frame_desc->layers[i];
+		for (int j = 0; j < drm_layer->nb_planes; j++) {
+			const AVDRMPlaneDescriptor *drm_plane = &drm_layer->planes[j];
+			const AVDRMObjectDescriptor *drm_object = &drm_frame_desc->objects[drm_plane->object_index];
+
+			uint32_t handle = 0;
+			int ret = drmPrimeFDToHandle(drm_fd, drm_object->fd, &handle);
+			if (ret < 0) {
+				perror("drmPrimeFDToHandle");
+				return 0;
+			}
+
+			handles[k] = handle;
+			pitches[k] = drm_plane->pitch;
+			offsets[k] = drm_plane->offset;
+			k++;
+		}
+	}
+
+	uint32_t fb_id = 0;
+	int ret = drmModeAddFB2(drm_fd, width, height, drm_format,
+		handles, pitches, offsets, &fb_id, 0);
+	if (ret < 0) {
+		perror("drmModeAddFB2");
+		return 0;
+	}
+
+	return fb_id;
+}
+
 int main(int argc, char *argv[]) {
 	if (argc < 2) {
 		fprintf(stderr, "usage: %s <file>\n", argv[0]);
@@ -218,6 +305,17 @@ int main(int argc, char *argv[]) {
 		return 1;
 	}
 
+	int drm_fd = open("/dev/dri/card0", O_RDWR);
+	if (drm_fd < 0) {
+		fprintf(stderr, "Failed to open DRM primary node\n");
+		return 1;
+	}
+
+	uint32_t crtc_id = pick_crtc(drm_fd);
+	if (crtc_id == 0) {
+		return 1;
+	}
+
 	AVFrame *frame = NULL;
 	ret = decode_frame(input_ctx, video_stream, decoder_ctx, &frame);
 	if (ret < 0) {
@@ -240,14 +338,19 @@ int main(int argc, char *argv[]) {
 	AVDRMFrameDescriptor *drm_frame_desc = (void *)drm_frame->data[0];
 	print_drm_frame_desc(drm_frame_desc);
 
-	// VA-API drivers may use separate layers with one plane each, or a single
-	// layer with multiple planes. We need to handle both.
-	uint32_t drm_format = get_drm_frame_format(drm_frame_desc);
-	if (drm_format == DRM_FORMAT_INVALID) {
-		fprintf(stderr, "Failed to get DRM frame format\n");
+	uint32_t fb_id = import_drm_frame_desc(drm_frame_desc, drm_fd,
+		drm_frame->width, drm_frame->height);
+	if (!fb_id) {
 		return 1;
 	}
-	fprintf(stderr, "DRM format: 0x%X\n", drm_format);
+
+	ret = drmModePageFlip(drm_fd, crtc_id, fb_id, 0, NULL);
+	if (ret < 0) {
+		perror("drmModePageFlip");
+		return 1;
+	}
+
+	sleep(5);
 
 	av_frame_free(&drm_frame);
 	av_frame_free(&frame);
-- 
2.34.2