egl: Add a simple cache for driver probe.

In current design, multiple drivers will probe the same display and the
best driver is determined.  The cache can be used by the drivers to
store and share the probed data.

src/egl/main/egldriver.c

@@ -113,6 +113,13 @@ library_suffix(void)
 #endif
 
 
+#define NUM_PROBE_CACHE_SLOTS 8
+static struct {
+   EGLint keys[NUM_PROBE_CACHE_SLOTS];
+   const void *values[NUM_PROBE_CACHE_SLOTS];
+} _eglProbeCache;
+
+
 /**
  * Open the named driver and find its bootstrap function: _eglMain().
  */
@@ -569,3 +576,44 @@ _eglFindAPIs(void)
 
    return mask;
 }
+
+
+/**
+ * Set the probe cache at the given key.
+ *
+ * A key, instead of a _EGLDriver, is used to allow the probe cache to be share
+ * by multiple drivers.
+ */
+void
+_eglSetProbeCache(EGLint key, const void *val)
+{
+   EGLint idx;
+
+   for (idx = 0; idx < NUM_PROBE_CACHE_SLOTS; idx++) {
+      if (!_eglProbeCache.keys[idx] || _eglProbeCache.keys[idx] == key)
+         break;
+   }
+   assert(key > 0);
+   assert(idx < NUM_PROBE_CACHE_SLOTS);
+
+   _eglProbeCache.keys[idx] = key;
+   _eglProbeCache.values[idx] = val;
+}
+
+
+/**
+ * Return the probe cache at the given key.
+ */
+const void *
+_eglGetProbeCache(EGLint key)
+{
+   EGLint idx;
+
+   for (idx = 0; idx < NUM_PROBE_CACHE_SLOTS; idx++) {
+      if (!_eglProbeCache.keys[idx] || _eglProbeCache.keys[idx] == key)
+         break;
+   }
+
+   return (idx < NUM_PROBE_CACHE_SLOTS && _eglProbeCache.keys[idx] == key) ?
+      _eglProbeCache.values[idx] : NULL;
+}

src/egl/main/egldriver.h

@@ -66,4 +66,12 @@ PUBLIC EGLint
 _eglFindAPIs(void);
 
 
+PUBLIC void
+_eglSetProbeCache(EGLint key, const void *val);
+
+
+PUBLIC const void *
+_eglGetProbeCache(EGLint key);
+
+
 #endif /* EGLDRIVER_INCLUDED */