gbm_gralloc: Add feature to search for KMS DRI card

Most modern SOCs have separate IP cores for GPU and Display Unit (KMS).
To work properly mesa requires initialize gbm interface using KMS card.
Mesa uses it to allocate buffers with SCANOUT flag and does not require
fd or pathname explicitly specified for GPU. Mesa will search for GPU and
load the proper driver.

Also, there is no warranty that the KMS card will always have
/dev/dri/card0 path and GPU - /dev/dri/card1. Order can depend on many
factors. For example: on the rpi4 board, it was observed that enabling
the WIFI kernel module swapping the card order. Therefore searching for
the KMS card is the only efficient solution.

The is_kms_dev function returns true when the libdrm function is returned
resources and the target device has at least one CTRC, connector, and
encoder. The open_first_kms_dev function returns opened file descriptor
on success using the previous function to check for each device. It also
returns zeroed value for the case of KMS absence, or the -EINVAL on glob
function error.

In the case of absence of the "hwc.drm.device" system property the first
KMS device or the default path /dev/dri/renderD128 will be used to open.

Signed-off-by: Matvii Zorin <[email protected]>
Reviewed-by: Roman Stratiienko <[email protected]>

gralloc_gbm.cpp

@@ -35,6 +35,8 @@
 #include <sys/stat.h>
 #include <fcntl.h>
 #include <assert.h>
+#include <xf86drmMode.h>
+#include <glob.h>
 
 #include <hardware/gralloc.h>
 #include <system/graphics.h>
@@ -311,10 +313,23 @@ struct gbm_device *gbm_dev_create(void)
 {
 	struct gbm_device *gbm;
 	char path[PROPERTY_VALUE_MAX];
+	int path_len;
 	int fd;
 
-	property_get("gralloc.gbm.device", path, "/dev/dri/renderD128");
-	fd = open(path, O_RDWR | O_CLOEXEC);
+	path_len = property_get("gralloc.gbm.device", path, "/dev/dri/card*");
+	/* Search for KMS device with the pattern or open it from property */
+	if (path[path_len - 1] == '*') {
+		fd = open_first_kms_dev(path);
+	} else {
+		fd = open(path, O_RDWR | O_CLOEXEC);
+	}
+
+	/* Open default path when KMS device wasn't found */
+	if (!fd) {
+		strcpy(path, "/dev/dri/renderD128");
+		fd = open(path, O_RDWR | O_CLOEXEC);
+	}
+
 	if (fd < 0) {
 		ALOGE("failed to open %s", path);
 		return NULL;
@@ -529,3 +544,49 @@ int gralloc_gbm_bo_lock_ycbcr(buffer_handle_t handle,
 
 	return 0;
 }
+
+/*
+ * Check if target device has KMS.
+ */
+bool is_kms_dev(int fd)
+{
+	auto res = drmModeGetResources(fd);
+	if (!res)
+		return false;
+
+	bool is_kms = res->count_crtcs > 0 && res->count_connectors > 0 &&
+			res->count_encoders > 0;
+
+	drmModeFreeResources(res);
+
+	return is_kms;
+}
+
+/*
+ * Search for a KMS device. Return opened file descriptor on success.
+ */
+int open_first_kms_dev(const char *pattern)
+{
+	glob_t glob_buf;
+	memset(&glob_buf, 0, sizeof(glob_buf));
+	int fd;
+
+	int ret = glob(pattern, 0, NULL, &glob_buf);
+	if (ret) {
+		globfree(&glob_buf);
+		return -EINVAL;
+	}
+
+	for (size_t i = 0; i < glob_buf.gl_pathc; ++i) {
+		fd = open(glob_buf.gl_pathv[i], O_RDWR | O_CLOEXEC);
+		if (fd < 0 || is_kms_dev(fd))
+			break;
+
+		close(fd);
+		fd = 0;
+	}
+
+	globfree(&glob_buf);
+
+	return fd;
+}

gralloc_gbm_priv.h

@@ -51,6 +51,9 @@ int gralloc_gbm_bo_lock_ycbcr(buffer_handle_t handle, int usage,
 struct gbm_device *gbm_dev_create(void);
 void gbm_dev_destroy(struct gbm_device *gbm);
 
+bool is_kms_dev(int fd);
+int open_first_kms_dev(const char *pattern);
+
 #ifdef __cplusplus
 }
 #endif