drm/bochs: support changing byteorder at mode set time

Add bochs_hw_set_*_endian() helper functions, to set the framebuffer
byteorder at mode set time.  Support both DRM_FORMAT_XRGB8888 and
DRM_FORMAT_BGRX8888 framebuffer formats, no matter what the native
machine byte order is.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20180921134704.12826-5-kraxel@redhat.com

drivers/gpu/drm/bochs/bochs_kms.c

@@ -77,7 +77,10 @@ static int bochs_crtc_mode_set(struct drm_crtc *crtc,
 	struct bochs_device *bochs =
 		container_of(crtc, struct bochs_device, crtc);
 
-	bochs_hw_setmode(bochs, mode);
+	if (WARN_ON(crtc->primary->fb == NULL))
+		return -EINVAL;
+
+	bochs_hw_setmode(bochs, mode, crtc->primary->fb->format);
 	bochs_crtc_mode_set_base(crtc, x, y, old_fb);
 	return 0;
 }
@@ -127,7 +130,8 @@ static const struct drm_crtc_helper_funcs bochs_helper_funcs = {
 };
 
 static const uint32_t bochs_formats[] = {
-	DRM_FORMAT_HOST_XRGB8888,
+	DRM_FORMAT_XRGB8888,
+	DRM_FORMAT_BGRX8888,
 };
 
 static struct drm_plane *bochs_primary_plane(struct drm_device *dev)