[Mesa-dev] [PATCH] egl/android: rework device probing

[Emil Velikov]

From: Emil Velikov <emil.velikov at collabora.com>

Unlike the other platforms, here we aim do guess if the device that we
somewhat arbitrarily picked, is supported or not.

In particular: when a vendor is _not_ requested we loop through all
devices, picking the first one which can create a DRI screen.

When a vendor is requested - we use that and do _not_ fall-back to any
other device.

The former seems a bit fiddly, but considering EGL_EXT_explicit_device and
EGL_MESA_query_renderer are MIA, this is the best we can do for the
moment.

With those (proposed) extensions userspace will be able to create a
separate EGL display for each device, query device details and make the
conscious decision which one to use.

Cc: Robert Foss <robert.foss at collabora.com>
Cc: Tomasz Figa <tfiga at chromium.org>
Signed-off-by: Emil Velikov <emil.velikov at collabora.com>
---
Thanks for the clarification Tomasz. The original code was using a
fall-back even a vendor was explicitly requested, confusing me a bit ;-)
---
 src/egl/drivers/dri2/platform_android.c | 71 +++++++++++++++----------
 1 file changed, 43 insertions(+), 28 deletions(-)

diff --git a/src/egl/drivers/dri2/platform_android.c b/src/egl/drivers/dri2/platform_android.c
index 1f9fe27ab85..5bf627dec7d 100644
--- a/src/egl/drivers/dri2/platform_android.c
+++ b/src/egl/drivers/dri2/platform_android.c
@@ -1420,13 +1420,32 @@ droid_filter_device(_EGLDisplay *disp, int fd, const char *vendor)
    return 0;
 }
 
+static int
+droid_probe_device(_EGLDisplay *disp)
+{
+  /* Check that the device is supported, by attempting to:
+   * - load the dri module
+   * - and, create a screen
+   */
+   if (!droid_load_driver(disp)) {
+      _eglLog(_EGL_WARNING, "DRI2: failed to load driver");
+      return -1;
+   }
+
+   if (!dri2_create_screen(disp)) {
+      _eglLog(_EGL_WARNING, "DRI2: failed to create screen");
+      return -1;
+   }
+   return 0;
+}
+
 static int
 droid_open_device(_EGLDisplay *disp)
 {
 #define MAX_DRM_DEVICES 32
    drmDevicePtr device, devices[MAX_DRM_DEVICES] = { NULL };
    int prop_set, num_devices;
-   int fd = -1, fallback_fd = -1;
+   int fd = -1;
 
    char *vendor_name = NULL;
    char vendor_buf[PROPERTY_VALUE_MAX];
@@ -1451,33 +1470,39 @@ droid_open_device(_EGLDisplay *disp)
          continue;
       }
 
-      if (vendor_name && droid_filter_device(disp, fd, vendor_name)) {
-         /* Match requested, but not found - set as fallback */
-         if (fallback_fd == -1) {
-            fallback_fd = fd;
-         } else {
+      /* If a vendor is explicitly provided, we use only that.
+       * Otherwise we fall-back the first device that is supported.
+       */
+      if (vendor_name) {
+         if (droid_filter_device(disp, fd, vendor_name)) {
+            /* Device does not match - try next device */
             close(fd);
             fd = -1;
+            continue;
          }
-
+         /* If the requested device matches use it, regardless if
+          * init fails. Do not fall-back to any other device.
+          */
+         if (droid_probbe_device(disp)) {
+            close(fd);
+            fd = -1;
+         }
+         break;
+      }
+      /* No explicit request - attempt the next device */
+      if (droid_probbe_device(disp)) {
+         close(fd);
+         fd = -1;
          continue;
       }
-      /* Found a device */
       break;
    }
    drmFreeDevices(devices, num_devices);
 
-   if (fallback_fd < 0 && fd < 0) {
-      _eglLog(_EGL_WARNING, "Failed to open any DRM device");
-      return -1;
-   }
-
-   if (fd < 0) {
-      _eglLog(_EGL_WARNING, "Failed to open desired DRM device, using fallback");
-      return fallback_fd;
-   }
+   if (fd < 0)
+      _eglLog(_EGL_WARNING, "Failed to open %s DRM device",
+            vendor_name ? "desired": "any");
 
-   close(fallback_fd);
    return fd;
 #undef MAX_DRM_DEVICES
 }
@@ -1519,16 +1544,6 @@ dri2_initialize_android(_EGLDriver *drv, _EGLDisplay *disp)
       goto cleanup;
    }
 
-   if (!droid_load_driver(disp)) {
-      err = "DRI2: failed to load driver";
-      goto cleanup;
-   }
-
-   if (!dri2_create_screen(disp)) {
-      err = "DRI2: failed to create screen";
-      goto cleanup;
-   }
-
    if (!dri2_setup_extensions(disp)) {
       err = "DRI2: failed to setup extensions";
       goto cleanup;
-- 
2.18.0