drm/fb-helper: Replace bpp/depth parameter by color mode

Replace the combination of bpp and depth with a single color-mode
argument. Handle special cases in simpledrm and ofdrm. Hard-code
XRGB8888 as fallback format for cases where no given format works.

The color-mode argument accepts the same values as the kernel's video
parameter. These are mostly bpp values between 1 and 32. The exceptions
are 15, which has a color depth of 15 and a bpp value of 16; and 32,
which has a color depth of 24 and a bpp value of 32.

v4:
	* add back lost test for bpp_specified (Maira)
	* add Fixes tag (Daniel)
v3:
	* fix ofdrm build (Maxime)
v2:
	* minimize changes (Daniel)
	* use drm_driver_legacy_fb_format() (Daniel)
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Tested-by: Maíra Canal <mcanal@igalia.com> # vc4 and vkms
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Fixes: 37c90d58 ("drm/fb-helper: Fix single-probe color-format selection")
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Javier Martinez Canillas <javierm@redhat.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230106112324.22055-1-tzimmermann@suse.de

drivers/gpu/drm/drm_fb_helper.c

@@ -1756,24 +1756,21 @@ static uint32_t drm_fb_helper_find_format(struct drm_fb_helper *fb_helper, const
 	return DRM_FORMAT_INVALID;
 }
 
-static uint32_t drm_fb_helper_find_cmdline_format(struct drm_fb_helper *fb_helper,
+static uint32_t drm_fb_helper_find_color_mode_format(struct drm_fb_helper *fb_helper,
 						     const uint32_t *formats, size_t format_count,
-						  const struct drm_cmdline_mode *cmdline_mode)
+						     unsigned int color_mode)
 {
 	struct drm_device *dev = fb_helper->dev;
 	uint32_t bpp, depth;
 
-	if (!cmdline_mode->bpp_specified)
-		return DRM_FORMAT_INVALID;
-
-	switch (cmdline_mode->bpp) {
+	switch (color_mode) {
 	case 1:
 	case 2:
 	case 4:
 	case 8:
 	case 16:
 	case 24:
-		bpp = depth = cmdline_mode->bpp;
+		bpp = depth = color_mode;
 		break;
 	case 15:
 		bpp = 16;
@@ -1784,7 +1781,7 @@ static uint32_t drm_fb_helper_find_cmdline_format(struct drm_fb_helper *fb_helpe
 		depth = 24;
 		break;
 	default:
-		drm_info(dev, "unsupported bpp value of %d\n", cmdline_mode->bpp);
+		drm_info(dev, "unsupported color mode of %d\n", color_mode);
 		return DRM_FORMAT_INVALID;
 	}
 
@@ -1817,10 +1814,13 @@ static int __drm_fb_helper_find_sizes(struct drm_fb_helper *fb_helper, int prefe
 		drm_client_for_each_connector_iter(connector, &conn_iter) {
 			struct drm_cmdline_mode *cmdline_mode = &connector->cmdline_mode;
 
-			surface_format = drm_fb_helper_find_cmdline_format(fb_helper,
+			if (!cmdline_mode->bpp_specified)
+				continue;
+
+			surface_format = drm_fb_helper_find_color_mode_format(fb_helper,
 									      plane->format_types,
 									      plane->format_count,
-									   cmdline_mode);
+									      cmdline_mode->bpp);
 			if (surface_format != DRM_FORMAT_INVALID)
 				break; /* found supported format */
 		}
@@ -1829,17 +1829,23 @@ static int __drm_fb_helper_find_sizes(struct drm_fb_helper *fb_helper, int prefe
 		if (surface_format != DRM_FORMAT_INVALID)
 			break; /* found supported format */
 
-		/* try preferred bpp/depth */
-		surface_format = drm_fb_helper_find_format(fb_helper, plane->format_types,
-							   plane->format_count, preferred_bpp,
-							   dev->mode_config.preferred_depth);
+		/* try preferred color mode */
+		surface_format = drm_fb_helper_find_color_mode_format(fb_helper,
+								      plane->format_types,
+								      plane->format_count,
+								      preferred_bpp);
 		if (surface_format != DRM_FORMAT_INVALID)
 			break; /* found supported format */
 	}
 
 	if (surface_format == DRM_FORMAT_INVALID) {
+		/*
+		 * If none of the given color modes works, fall back
+		 * to XRGB8888. Drivers are expected to provide this
+		 * format for compatibility with legacy applications.
+		 */
 		drm_warn(dev, "No compatible format found\n");
-		return -EAGAIN;
+		surface_format = drm_driver_legacy_fb_format(dev, 32, 24);
 	}
 
 	info = drm_format_info(surface_format);

drivers/gpu/drm/tiny/ofdrm.c

@@ -1352,6 +1352,7 @@ static int ofdrm_probe(struct platform_device *pdev)
 {
 	struct ofdrm_device *odev;
 	struct drm_device *dev;
+	unsigned int color_mode;
 	int ret;
 
 	odev = ofdrm_device_create(&ofdrm_driver, pdev);
@@ -1363,7 +1364,11 @@ static int ofdrm_probe(struct platform_device *pdev)
 	if (ret)
 		return ret;
 
-	drm_fbdev_generic_setup(dev, drm_format_info_bpp(odev->format, 0));
+	color_mode = drm_format_info_bpp(odev->format, 0);
+	if (color_mode == 16)
+		color_mode = odev->format->depth; // can be 15 or 16
+
+	drm_fbdev_generic_setup(dev, color_mode);
 
 	return 0;
 }

drivers/gpu/drm/tiny/simpledrm.c

@@ -802,6 +802,7 @@ static int simpledrm_probe(struct platform_device *pdev)
 {
 	struct simpledrm_device *sdev;
 	struct drm_device *dev;
+	unsigned int color_mode;
 	int ret;
 
 	sdev = simpledrm_device_create(&simpledrm_driver, pdev);
@@ -813,7 +814,11 @@ static int simpledrm_probe(struct platform_device *pdev)
 	if (ret)
 		return ret;
 
-	drm_fbdev_generic_setup(dev, drm_format_info_bpp(sdev->format, 0));
+	color_mode = drm_format_info_bpp(sdev->format, 0);
+	if (color_mode == 16)
+		color_mode = sdev->format->depth; // can be 15 or 16
+
+	drm_fbdev_generic_setup(dev, color_mode);
 
 	return 0;
 }