drm/nouveau/fbcon: add module parameter to select bits-per-pixel

Useful for debugging.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_fbcon.c

@@ -56,6 +56,10 @@ MODULE_PARM_DESC(nofbaccel, "Disable fbcon acceleration");
 int nouveau_nofbaccel = 0;
 module_param_named(nofbaccel, nouveau_nofbaccel, int, 0400);
 
+MODULE_PARM_DESC(fbcon_bpp, "fbcon bits-per-pixel (default: auto)");
+static int nouveau_fbcon_bpp;
+module_param_named(fbcon_bpp, nouveau_fbcon_bpp, int, 0400);
+
 static void
 nouveau_fbcon_fillrect(struct fb_info *info, const struct fb_fillrect *rect)
 {
@@ -488,7 +492,7 @@ nouveau_fbcon_init(struct drm_device *dev)
 {
 	struct nouveau_drm *drm = nouveau_drm(dev);
 	struct nouveau_fbdev *fbcon;
-	int preferred_bpp;
+	int preferred_bpp = nouveau_fbcon_bpp;
 	int ret;
 
 	if (!dev->mode_config.num_crtc ||
@@ -512,13 +516,15 @@ nouveau_fbcon_init(struct drm_device *dev)
 	if (ret)
 		goto fini;
 
-	if (drm->client.device.info.ram_size <= 32 * 1024 * 1024)
-		preferred_bpp = 8;
-	else
-	if (drm->client.device.info.ram_size <= 64 * 1024 * 1024)
-		preferred_bpp = 16;
-	else
-		preferred_bpp = 32;
+	if (preferred_bpp != 8 && preferred_bpp != 16 && preferred_bpp != 32) {
+		if (drm->client.device.info.ram_size <= 32 * 1024 * 1024)
+			preferred_bpp = 8;
+		else
+		if (drm->client.device.info.ram_size <= 64 * 1024 * 1024)
+			preferred_bpp = 16;
+		else
+			preferred_bpp = 32;
+	}
 
 	/* disable all the possible outputs/crtcs before entering KMS mode */
 	if (!drm_drv_uses_atomic_modeset(dev))