commit ec75ccd0735213423d6cf89409f8a3bfdaeddcee
author Matvii Zorin <matvii.zorin@globallogic.com> Fri Jul 17 12:08:45 2020 +0300
committer Matvii Zorin <matvii.zorin@globallogic.com> Fri Jul 24 11:08:18 2020 +0300
tree 080773381c0bfdf23fd6a217e68c280d097e26f3
parent 2619aabb8754718ce4469407afd3004bfdea768e

drm_hwcomposer: Add feature to search for KMS DRI card

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

drm/resourcemanager.cpp

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 @@
   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 @@
     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 @@
   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))