egl: add EGL_MESA_device_software support

Add a plain software device, which is always available.

We can safely assign it as the first/initial device in _eglGlobals,
although we ensure that's the case with a handful of _eglDeviceSupports
checks throughout the code.

v2:
 - s/_eglFindDevice/_eglAddDevice/ (Eric)
 - s/_eglLookupAllDevices/_eglRefreshDeviceList/ (Eric)
 - move ^^ helpers into a earlier patch (Eric, Mathias)
 - set the SW device on _eglGlobal init. (Eric)
 - add a number of _eglDeviceSupports checks (Mathias)
 - split Device/Display attach to a separate patch

v3:
 - flip inverted asserts (Mathias)
 - s/on-stack/static/ (Mathias)

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Mathias Fröhlich <Mathias.Froehlich@web.de>

src/egl/main/egldevice.c

@@ -37,6 +37,8 @@ struct _egl_device {
    _EGLDevice *Next;
 
    const char *extensions;
+
+   EGLBoolean MESA_device_software;
 };
 
 void
@@ -47,6 +49,12 @@ _eglFiniDevice(void)
    /* atexit function is called with global mutex locked */
 
    dev_list = _eglGlobal.DeviceList;
+
+   /* The first device is static allocated SW device */
+   assert(dev_list);
+   assert(_eglDeviceSupports(dev_list, _EGL_DEVICE_SOFTWARE));
+   dev_list = dev_list->Next;
+
    while (dev_list) {
       /* pop list head */
       dev = dev_list;
@@ -74,6 +82,11 @@ _eglCheckDeviceHandle(EGLDeviceEXT device)
    return (cur != NULL);
 }
 
+_EGLDevice _eglSoftwareDevice = {
+   .extensions = "EGL_MESA_device_software",
+   .MESA_device_software = EGL_TRUE,
+};
+
 /* Adds a device in DeviceList, if needed for the given fd.
  *
  * If a software device, the fd is ignored.
@@ -84,6 +97,13 @@ _eglAddDevice(int fd, bool software)
    _EGLDevice *dev;
 
    mtx_lock(_eglGlobal.Mutex);
+   dev = _eglGlobal.DeviceList;
+
+   /* The first device is always software */
+   assert(dev);
+   assert(_eglDeviceSupports(dev, _EGL_DEVICE_SOFTWARE));
+   if (software)
+      goto out;
 
    dev = NULL;
 
@@ -96,6 +116,8 @@ EGLBoolean
 _eglDeviceSupports(_EGLDevice *dev, _EGLDeviceExtension ext)
 {
    switch (ext) {
+   case _EGL_DEVICE_SOFTWARE:
+      return dev->MESA_device_software;
    default:
       assert(0);
       return EGL_FALSE;
@@ -140,6 +162,11 @@ _eglRefreshDeviceList(void)
 
    dev = _eglGlobal.DeviceList;
 
+   /* The first device is always software */
+   assert(dev);
+   assert(_eglDeviceSupports(dev, _EGL_DEVICE_SOFTWARE));
+   count++;
+
    return count;
 }
 

src/egl/main/egldevice.h

@@ -38,6 +38,8 @@
 extern "C" {
 #endif
 
+extern _EGLDevice _eglSoftwareDevice;
+
 void
 _eglFiniDevice(void);
 
@@ -57,7 +59,7 @@ _EGLDevice *
 _eglAddDevice(int fd, bool software);
 
 enum _egl_device_extension {
-   EGL_FOOBAR, /* A temporary entry, since enum with zero entries is illegal */
+   _EGL_DEVICE_SOFTWARE,
 };
 
 typedef enum _egl_device_extension _EGLDeviceExtension;

src/egl/main/eglglobals.c

@@ -52,6 +52,7 @@ struct _egl_global _eglGlobal =
 {
    .Mutex = &_eglGlobalMutex,
    .DisplayList = NULL,
+   .DeviceList = &_eglSoftwareDevice,
    .NumAtExitCalls = 3,
    .AtExitCalls = {
       /* default AtExitCalls, called in reverse order */