drm/vc4: Add a getparam to signal support for branches.

Userspace needs to know if it can create shaders that do branching.
Otherwise, for backwards compatibility with old kernels it needs to
lower if statements to conditional assignments.

Signed-off-by: Eric Anholt <eric@anholt.net>

drivers/gpu/drm/vc4/vc4_drv.c

@@ -76,6 +76,9 @@ static int vc4_get_param_ioctl(struct drm_device *dev, void *data,
 		args->value = V3D_READ(V3D_IDENT2);
 		pm_runtime_put(&vc4->v3d->pdev->dev);
 		break;
+	case DRM_VC4_PARAM_SUPPORTS_BRANCHES:
+		args->value = true;
+		break;
 	default:
 		DRM_DEBUG("Unknown parameter %d\n", args->param);
 		return -EINVAL;

include/uapi/drm/vc4_drm.h

@@ -285,6 +285,7 @@ struct drm_vc4_get_hang_state {
 #define DRM_VC4_PARAM_V3D_IDENT0		0
 #define DRM_VC4_PARAM_V3D_IDENT1		1
 #define DRM_VC4_PARAM_V3D_IDENT2		2
+#define DRM_VC4_PARAM_SUPPORTS_BRANCHES		3
 
 struct drm_vc4_get_param {
 	__u32 param;