drm_hwcomposer: Add feature to search for KMS DRI cardHEADmaster

Most modern SOCs have separate IP cores for GPU and Display Unit (KMS).
Also, there is no warranty that the KMS card will always have
/dev/dri/card0 path and GPU - /dev/dri/card1, but drm_hwcomposer should
open only KMS device. The 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 IsKMSDev function returns true when the file descriptor on the path
is successfully opened, the drmlib function is returned resources and
the target device has at least one CTRC, connector, and encoder. Also,
the patch enables finding KMS devices in the case of the absence of
the system property specification.

Signed-off-by: Matvii Zorin <matvii.zorin@globallogic.com>
Reviewed-by: Roman Stratiienko <r.stratiienko@gmail.com>
Change-Id: I8874a50188207833389fadd4815b42a80bf69240

2 files changed, 30 insertions, 2 deletions

diff --git a/drm/resourcemanager.cpp b/drm/resourcemanager.cpp
index da1a2db..382a85a 100644
--- a/drm/resourcemanager.cpp
+++ b/drm/resourcemanager.cpp
@@ -20,6 +20,7 @@
 
 #include <cutils/properties.h>
 #include <log/log.h>
+#include <sys/stat.h>
 #include <sstream>
 #include <string>
 
@@ -32,7 +33,7 @@ int ResourceManager::Init() {
   char path_pattern[PROPERTY_VALUE_MAX];
   // Could be a valid path or it can have at the end of it the wildcard %
   // which means that it will try open all devices until an error is met.
-  int path_len = property_get("hwc.drm.device", path_pattern, "/dev/dri/card0");
+  int path_len = property_get("hwc.drm.device", path_pattern, "/dev/dri/card%");
   int ret = 0;
   if (path_pattern[path_len - 1] != '%') {
     ret = AddDrmDevice(std::string(path_pattern));
@@ -41,7 +42,13 @@ int ResourceManager::Init() {
     for (int idx = 0; !ret; ++idx) {
       std::ostringstream path;
       path << path_pattern << idx;
-      ret = AddDrmDevice(path.str());
+
+      struct stat buf;
+      if (stat(path.str().c_str(), &buf)) {
+        break;
+      } else if (IsKMSDev(path.str().c_str())) {
+        ret = AddDrmDevice(path.str());
+      }
     }
   }
 
@@ -94,6 +101,26 @@ DrmConnector *ResourceManager::AvailableWritebackConnector(int display) {
   return writeback_conn;
 }
 
+bool ResourceManager::IsKMSDev(const char *path) {
+  int fd = open(path, O_RDWR | O_CLOEXEC);
+  if (fd < 0)
+    return false;
+
+  auto res = drmModeGetResources(fd);
+  if (!res) {
+    close(fd);
+    return false;
+  }
+
+  bool is_kms = res->count_crtcs > 0 && res->count_connectors > 0 &&
+                res->count_encoders > 0;
+
+  drmModeFreeResources(res);
+  close(fd);
+
+  return is_kms;
+}
+
 DrmDevice *ResourceManager::GetDrmDevice(int display) {
   for (auto &drm : drms_) {
     if (drm->HandlesDisplay(display))
diff --git a/include/resourcemanager.h b/include/resourcemanager.h
index 7a86828..9fefb46 100644
--- a/include/resourcemanager.h
+++ b/include/resourcemanager.h
@@ -46,6 +46,7 @@ class ResourceManager {
 
  private:
   int AddDrmDevice(std::string path);
+  static bool IsKMSDev(const char *path);
 
   int num_displays_;
   std::vector<std::unique_ptr<DrmDevice>> drms_;