drm: Define DRM_FORMAT_MAX_PLANES

DRM uses a magic number of 4 for the maximum number of planes per color
format. Declare this constant via DRM_FORMAT_MAX_PLANES and update the
related code. Some code depends on the length of arrays that are now
declared with DRM_FORMAT_MAX_PLANES. Convert it from '4' to ARRAY_SIZE.

v2:
	* mention usage of ARRAY_SIZE() in the commit message (Maxime)
	* also fix error handling in drm_gem_fb_init_with_funcs()
	  (kernel test robot)
	* include <drm/drm_fourcc.h> for DRM_FORMAT_MAX_PLANES
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210730183511.20080-2-tzimmermann@suse.de

drivers/gpu/drm/drm_gem_framebuffer_helper.c

@@ -48,7 +48,7 @@
 struct drm_gem_object *drm_gem_fb_get_obj(struct drm_framebuffer *fb,
 					  unsigned int plane)
 {
-	if (plane >= 4)
+	if (plane >= ARRAY_SIZE(fb->obj))
 		return NULL;
 
 	return fb->obj[plane];
@@ -62,7 +62,8 @@ drm_gem_fb_init(struct drm_device *dev,
 		 struct drm_gem_object **obj, unsigned int num_planes,
 		 const struct drm_framebuffer_funcs *funcs)
 {
-	int ret, i;
+	unsigned int i;
+	int ret;
 
 	drm_helper_mode_fill_fb_struct(dev, fb, mode_cmd);
 
@@ -86,9 +87,9 @@ drm_gem_fb_init(struct drm_device *dev,
  */
 void drm_gem_fb_destroy(struct drm_framebuffer *fb)
 {
-	int i;
+	size_t i;
 
-	for (i = 0; i < 4; i++)
+	for (i = 0; i < ARRAY_SIZE(fb->obj); i++)
 		drm_gem_object_put(fb->obj[i]);
 
 	drm_framebuffer_cleanup(fb);
@@ -145,8 +146,9 @@ int drm_gem_fb_init_with_funcs(struct drm_device *dev,
 			       const struct drm_framebuffer_funcs *funcs)
 {
 	const struct drm_format_info *info;
-	struct drm_gem_object *objs[4];
-	int ret, i;
+	struct drm_gem_object *objs[DRM_FORMAT_MAX_PLANES];
+	unsigned int i;
+	int ret;
 
 	info = drm_get_format_info(dev, mode_cmd);
 	if (!info) {
@@ -187,9 +189,10 @@ int drm_gem_fb_init_with_funcs(struct drm_device *dev,
 	return 0;
 
 err_gem_object_put:
-	for (i--; i >= 0; i--)
+	while (i > 0) {
+		--i;
 		drm_gem_object_put(objs[i]);
-
+	}
 	return ret;
 }
 EXPORT_SYMBOL_GPL(drm_gem_fb_init_with_funcs);

include/drm/drm_fourcc.h

@@ -25,6 +25,11 @@
 #include <linux/types.h>
 #include <uapi/drm/drm_fourcc.h>
 
+/**
+ * DRM_FORMAT_MAX_PLANES - maximum number of planes a DRM format can have
+ */
+#define DRM_FORMAT_MAX_PLANES	4u
+
 /*
  * DRM formats are little endian.  Define host endian variants for the
  * most common formats here, to reduce the #ifdefs needed in drivers.
@@ -78,7 +83,7 @@ struct drm_format_info {
 		 * triplet @char_per_block, @block_w, @block_h for better
 		 * describing the pixel format.
 		 */
-		u8 cpp[4];
+		u8 cpp[DRM_FORMAT_MAX_PLANES];
 
 		/**
 		 * @char_per_block:
@@ -104,7 +109,7 @@ struct drm_format_info {
 		 * information from their drm_mode_config.get_format_info hook
 		 * if they want the core to be validating the pitch.
 		 */
-		u8 char_per_block[4];
+		u8 char_per_block[DRM_FORMAT_MAX_PLANES];
 	};
 
 	/**
@@ -113,7 +118,7 @@ struct drm_format_info {
 	 * Block width in pixels, this is intended to be accessed through
 	 * drm_format_info_block_width()
 	 */
-	u8 block_w[4];
+	u8 block_w[DRM_FORMAT_MAX_PLANES];
 
 	/**
 	 * @block_h:
@@ -121,7 +126,7 @@ struct drm_format_info {
 	 * Block height in pixels, this is intended to be accessed through
 	 * drm_format_info_block_height()
 	 */
-	u8 block_h[4];
+	u8 block_h[DRM_FORMAT_MAX_PLANES];
 
 	/** @hsub: Horizontal chroma subsampling factor */
 	u8 hsub;

include/drm/drm_framebuffer.h

@@ -27,12 +27,12 @@
 #include <linux/list.h>
 #include <linux/sched.h>
 
+#include <drm/drm_fourcc.h>
 #include <drm/drm_mode_object.h>
 
 struct drm_clip_rect;
 struct drm_device;
 struct drm_file;
-struct drm_format_info;
 struct drm_framebuffer;
 struct drm_gem_object;
 
@@ -147,7 +147,7 @@ struct drm_framebuffer {
 	 * @pitches: Line stride per buffer. For userspace created object this
 	 * is copied from drm_mode_fb_cmd2.
 	 */
-	unsigned int pitches[4];
+	unsigned int pitches[DRM_FORMAT_MAX_PLANES];
 	/**
 	 * @offsets: Offset from buffer start to the actual pixel data in bytes,
 	 * per buffer. For userspace created object this is copied from
@@ -165,7 +165,7 @@ struct drm_framebuffer {
 	 * data (even for linear buffers). Specifying an x/y pixel offset is
 	 * instead done through the source rectangle in &struct drm_plane_state.
 	 */
-	unsigned int offsets[4];
+	unsigned int offsets[DRM_FORMAT_MAX_PLANES];
 	/**
 	 * @modifier: Data layout modifier. This is used to describe
 	 * tiling, or also special layouts (like compression) of auxiliary
@@ -210,7 +210,7 @@ struct drm_framebuffer {
 	 * This is used by the GEM framebuffer helpers, see e.g.
 	 * drm_gem_fb_create().
 	 */
-	struct drm_gem_object *obj[4];
+	struct drm_gem_object *obj[DRM_FORMAT_MAX_PLANES];
 };
 
 #define obj_to_fb(x) container_of(x, struct drm_framebuffer, base)

include/drm/drm_gem_atomic_helper.h

@@ -5,6 +5,7 @@
 
 #include <linux/dma-buf-map.h>
 
+#include <drm/drm_fourcc.h>
 #include <drm/drm_plane.h>
 
 struct drm_simple_display_pipe;
@@ -40,7 +41,7 @@ struct drm_shadow_plane_state {
 	 * The memory mappings stored in map should be established in the plane's
 	 * prepare_fb callback and removed in the cleanup_fb callback.
 	 */
-	struct dma_buf_map map[4];
+	struct dma_buf_map map[DRM_FORMAT_MAX_PLANES];
 };
 
 /**