drm: mxsfb: check framebuffer pitch

The lcdif IP does not support a framebuffer pitch (stride) other than
framebuffer width. Check for equality and reject the framebuffer
otherwise.

This prevents a distorted picture when using 640x800 and running the
Mesa graphics stack. Mesa tries to use a cache aligned stride, which
leads at that particular resolution to width != stride. Currently
Mesa has no fallback behavior, but rejecting this configuration allows
userspace to handle the issue correctly.

Fixes: 45d59d70 ("drm: Add new driver for MXSFB controller")
Signed-off-by: Stefan Agner <stefan@agner.ch>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200908141654.266836-1-stefan@agner.ch

drivers/gpu/drm/mxsfb/mxsfb_drv.c

@@ -21,6 +21,7 @@
 #include <drm/drm_connector.h>
 #include <drm/drm_drv.h>
 #include <drm/drm_fb_helper.h>
+#include <drm/drm_fourcc.h>
 #include <drm/drm_gem_cma_helper.h>
 #include <drm/drm_gem_framebuffer_helper.h>
 #include <drm/drm_irq.h>
@@ -81,8 +82,26 @@ void mxsfb_disable_axi_clk(struct mxsfb_drm_private *mxsfb)
 		clk_disable_unprepare(mxsfb->clk_axi);
 }
 
+static struct drm_framebuffer *
+mxsfb_fb_create(struct drm_device *dev, struct drm_file *file_priv,
+		const struct drm_mode_fb_cmd2 *mode_cmd)
+{
+	const struct drm_format_info *info;
+
+	info = drm_get_format_info(dev, mode_cmd);
+	if (!info)
+		return ERR_PTR(-EINVAL);
+
+	if (mode_cmd->width * info->cpp[0] != mode_cmd->pitches[0]) {
+		dev_dbg(dev->dev, "Invalid pitch: fb width must match pitch\n");
+		return ERR_PTR(-EINVAL);
+	}
+
+	return drm_gem_fb_create(dev, file_priv, mode_cmd);
+}
+
 static const struct drm_mode_config_funcs mxsfb_mode_config_funcs = {
-	.fb_create		= drm_gem_fb_create,
+	.fb_create		= mxsfb_fb_create,
 	.atomic_check		= drm_atomic_helper_check,
 	.atomic_commit		= drm_atomic_helper_commit,
 };