drm/fb-helper: Add support for DRM_FORMAT_C[124]

Add support for color-indexed frame buffer formats with two, four, and
sixteen colors to the DRM framebuffer helper functions:
  1. Add support for 1, 2, and 4 bits per pixel to the damage helper,
  2. For color-indexed modes, the length of the color bitfields must be
     set to the color depth, else the logo code may pick a logo with too
     many colors.  Drop the incorrect DAC width comment, which
     originates from the i915 driver.
  3. Accept C[124] modes when validating or filling in struct
     fb_var_screeninfo, and use the correct number of bits per pixel.
  4. Set the visual to FB_VISUAL_PSEUDOCOLOR for all color-indexed
     modes.
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/db3e80b445df661ff0cd7e698507a8d24a4c867e.1657294931.git.geert@linux-m68k.org

drivers/gpu/drm/drm_fb_helper.c

@@ -377,12 +377,31 @@ static void drm_fb_helper_damage_blit_real(struct drm_fb_helper *fb_helper,
 					   struct iosys_map *dst)
 {
 	struct drm_framebuffer *fb = fb_helper->fb;
-	unsigned int cpp = fb->format->cpp[0];
-	size_t offset = clip->y1 * fb->pitches[0] + clip->x1 * cpp;
-	void *src = fb_helper->fbdev->screen_buffer + offset;
-	size_t len = (clip->x2 - clip->x1) * cpp;
+	size_t offset = clip->y1 * fb->pitches[0];
+	size_t len = clip->x2 - clip->x1;
 	unsigned int y;
+	void *src;
 
+	switch (drm_format_info_bpp(fb->format, 0)) {
+	case 1:
+		offset += clip->x1 / 8;
+		len = DIV_ROUND_UP(len + clip->x1 % 8, 8);
+		break;
+	case 2:
+		offset += clip->x1 / 4;
+		len = DIV_ROUND_UP(len + clip->x1 % 4, 4);
+		break;
+	case 4:
+		offset += clip->x1 / 2;
+		len = DIV_ROUND_UP(len + clip->x1 % 2, 2);
+		break;
+	default:
+		offset += clip->x1 * fb->format->cpp[0];
+		len *= fb->format->cpp[0];
+		break;
+	}
+
+	src = fb_helper->fbdev->screen_buffer + offset;
 	iosys_map_incr(dst, offset); /* go to first pixel within clip rect */
 
 	for (y = clip->y1; y < clip->y2; y++) {
@@ -1274,19 +1293,23 @@ static bool drm_fb_pixel_format_equal(const struct fb_var_screeninfo *var_1,
 }
 
 static void drm_fb_helper_fill_pixel_fmt(struct fb_var_screeninfo *var,
-					 u8 depth)
+					 const struct drm_format_info *format)
 {
-	switch (depth) {
-	case 8:
+	u8 depth = format->depth;
+
+	if (format->is_color_indexed) {
 		var->red.offset = 0;
 		var->green.offset = 0;
 		var->blue.offset = 0;
-		var->red.length = 8; /* 8bit DAC */
-		var->green.length = 8;
-		var->blue.length = 8;
+		var->red.length = depth;
+		var->green.length = depth;
+		var->blue.length = depth;
 		var->transp.offset = 0;
 		var->transp.length = 0;
-		break;
+		return;
+	}
+
+	switch (depth) {
 	case 15:
 		var->red.offset = 10;
 		var->green.offset = 5;
@@ -1341,7 +1364,9 @@ int drm_fb_helper_check_var(struct fb_var_screeninfo *var,
 {
 	struct drm_fb_helper *fb_helper = info->par;
 	struct drm_framebuffer *fb = fb_helper->fb;
+	const struct drm_format_info *format = fb->format;
 	struct drm_device *dev = fb_helper->dev;
+	unsigned int bpp;
 
 	if (in_dbg_master())
 		return -EINVAL;
@@ -1351,22 +1376,33 @@ int drm_fb_helper_check_var(struct fb_var_screeninfo *var,
 		var->pixclock = 0;
 	}
 
-	if ((drm_format_info_block_width(fb->format, 0) > 1) ||
-	    (drm_format_info_block_height(fb->format, 0) > 1))
-		return -EINVAL;
+	switch (format->format) {
+	case DRM_FORMAT_C1:
+	case DRM_FORMAT_C2:
+	case DRM_FORMAT_C4:
+		/* supported format with sub-byte pixels */
+		break;
+
+	default:
+		if ((drm_format_info_block_width(format, 0) > 1) ||
+		    (drm_format_info_block_height(format, 0) > 1))
+			return -EINVAL;
+		break;
+	}
 
 	/*
 	 * Changes struct fb_var_screeninfo are currently not pushed back
 	 * to KMS, hence fail if different settings are requested.
 	 */
-	if (var->bits_per_pixel > fb->format->cpp[0] * 8 ||
+	bpp = drm_format_info_bpp(format, 0);
+	if (var->bits_per_pixel > bpp ||
 	    var->xres > fb->width || var->yres > fb->height ||
 	    var->xres_virtual > fb->width || var->yres_virtual > fb->height) {
 		drm_dbg_kms(dev, "fb requested width/height/bpp can't fit in current fb "
 			  "request %dx%d-%d (virtual %dx%d) > %dx%d-%d\n",
 			  var->xres, var->yres, var->bits_per_pixel,
 			  var->xres_virtual, var->yres_virtual,
-			  fb->width, fb->height, fb->format->cpp[0] * 8);
+			  fb->width, fb->height, bpp);
 		return -EINVAL;
 	}
 
@@ -1381,13 +1417,13 @@ int drm_fb_helper_check_var(struct fb_var_screeninfo *var,
 	    !var->blue.length    && !var->transp.length   &&
 	    !var->red.msb_right  && !var->green.msb_right &&
 	    !var->blue.msb_right && !var->transp.msb_right) {
-		drm_fb_helper_fill_pixel_fmt(var, fb->format->depth);
+		drm_fb_helper_fill_pixel_fmt(var, format);
 	}
 
 	/*
 	 * Likewise, bits_per_pixel should be rounded up to a supported value.
 	 */
-	var->bits_per_pixel = fb->format->cpp[0] * 8;
+	var->bits_per_pixel = bpp;
 
 	/*
 	 * drm fbdev emulation doesn't support changing the pixel format at all,
@@ -1723,11 +1759,11 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper,
 }
 
 static void drm_fb_helper_fill_fix(struct fb_info *info, uint32_t pitch,
-				   uint32_t depth)
+				   bool is_color_indexed)
 {
 	info->fix.type = FB_TYPE_PACKED_PIXELS;
-	info->fix.visual = depth == 8 ? FB_VISUAL_PSEUDOCOLOR :
-		FB_VISUAL_TRUECOLOR;
+	info->fix.visual = is_color_indexed ? FB_VISUAL_PSEUDOCOLOR
+					    : FB_VISUAL_TRUECOLOR;
 	info->fix.mmio_start = 0;
 	info->fix.mmio_len = 0;
 	info->fix.type_aux = 0;
@@ -1744,19 +1780,31 @@ static void drm_fb_helper_fill_var(struct fb_info *info,
 				   uint32_t fb_width, uint32_t fb_height)
 {
 	struct drm_framebuffer *fb = fb_helper->fb;
+	const struct drm_format_info *format = fb->format;
+
+	switch (format->format) {
+	case DRM_FORMAT_C1:
+	case DRM_FORMAT_C2:
+	case DRM_FORMAT_C4:
+		/* supported format with sub-byte pixels */
+		break;
+
+	default:
+		WARN_ON((drm_format_info_block_width(format, 0) > 1) ||
+			(drm_format_info_block_height(format, 0) > 1));
+		break;
+	}
 
-	WARN_ON((drm_format_info_block_width(fb->format, 0) > 1) ||
-		(drm_format_info_block_height(fb->format, 0) > 1));
 	info->pseudo_palette = fb_helper->pseudo_palette;
 	info->var.xres_virtual = fb->width;
 	info->var.yres_virtual = fb->height;
-	info->var.bits_per_pixel = fb->format->cpp[0] * 8;
+	info->var.bits_per_pixel = drm_format_info_bpp(format, 0);
 	info->var.accel_flags = FB_ACCELF_TEXT;
 	info->var.xoffset = 0;
 	info->var.yoffset = 0;
 	info->var.activate = FB_ACTIVATE_NOW;
 
-	drm_fb_helper_fill_pixel_fmt(&info->var, fb->format->depth);
+	drm_fb_helper_fill_pixel_fmt(&info->var, format);
 
 	info->var.xres = fb_width;
 	info->var.yres = fb_height;
@@ -1781,7 +1829,8 @@ void drm_fb_helper_fill_info(struct fb_info *info,
 {
 	struct drm_framebuffer *fb = fb_helper->fb;
 
-	drm_fb_helper_fill_fix(info, fb->pitches[0], fb->format->depth);
+	drm_fb_helper_fill_fix(info, fb->pitches[0],
+			       fb->format->is_color_indexed);
 	drm_fb_helper_fill_var(info, fb_helper,
 			       sizes->fb_width, sizes->fb_height);