Mesa (main): gbm: Load backend based on DRM device driver name

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Module: Mesa
Branch: main
Commit: 21ce1ca846698527093b0f8b95a57c550f984ab1
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=21ce1ca846698527093b0f8b95a57c550f984ab1

Author: James Jones <jajones at nvidia.com>
Date:   Thu Mar 18 15:36:07 2021 -0700

gbm: Load backend based on DRM device driver name

After attempting to use the GBM backend specified by the user
via an environment variable, if any, but before falling back
to the built-in GBM backends, attempt to dlopen
libg<DRM driver name>_gbm.so in the GBM backend library search
path (Defaults to "$libdir/gbm") and initialize a device using
it. This enables automatic backend discovery for devices that
do not provide a DRI driver.

Signed-off-by: James Jones <jajones at nvidia.com>
Reviewed-by: Michel Dänzer <mdaenzer at redhat.com>
Reviewed-by: Emil Velikov <emil.l.velikov at gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9902>

---

 src/gbm/main/backend.c | 30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/src/gbm/main/backend.c b/src/gbm/main/backend.c
index b628c403faa..974d0a76a4e 100644
--- a/src/gbm/main/backend.c
+++ b/src/gbm/main/backend.c
@@ -34,6 +34,7 @@
 #include <limits.h>
 #include <assert.h>
 #include <dlfcn.h>
+#include <xf86drm.h>
 
 #include "loader.h"
 #include "backend.h"
@@ -53,6 +54,7 @@ static const struct gbm_backend_desc builtin_backends[] = {
    { "dri", &gbm_dri_backend },
 };
 
+#define BACKEND_LIB_SUFFIX "_gbm"
 static const char *backend_search_path_vars[] = {
    "GBM_BACKENDS_PATH",
    NULL
@@ -161,7 +163,7 @@ find_backend(const char *name, int fd)
    }
 
    if (name && !dev) {
-      lib = loader_open_driver_lib(name, "_gbm",
+      lib = loader_open_driver_lib(name, BACKEND_LIB_SUFFIX,
                                    backend_search_path_vars,
                                    DEFAULT_BACKENDS_PATH,
                                    true);
@@ -186,6 +188,29 @@ override_backend(int fd)
    return dev;
 }
 
+static struct gbm_device *
+backend_from_driver_name(int fd)
+{
+   struct gbm_device *dev = NULL;
+   drmVersionPtr v = drmGetVersion(fd);
+   void *lib;
+
+   if (!v)
+      return NULL;
+
+   lib = loader_open_driver_lib(v->name, BACKEND_LIB_SUFFIX,
+                                backend_search_path_vars,
+                                DEFAULT_BACKENDS_PATH,
+                                false);
+
+   if (lib)
+      dev = load_backend(lib, fd, v->name);
+
+   drmFreeVersion(v);
+
+   return dev;
+}
+
 struct gbm_device *
 _gbm_create_device(int fd)
 {
@@ -193,6 +218,9 @@ _gbm_create_device(int fd)
 
    dev = override_backend(fd);
 
+   if (!dev)
+      dev = backend_from_driver_name(fd);
+
    if (!dev)
       dev = find_backend(NULL, fd);