linux-kernel - [PATCH v3] drm: mxsfb: check framebuffer pitch

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Message-Id: <20200908141654.266836-1-stefan@agner.ch>
Date:   Tue,  8 Sep 2020 16:16:54 +0200
From:   Stefan Agner <stefan@...er.ch>
To:     marex@...x.de, stefan@...er.ch
Cc:     laurent.pinchart@...asonboard.com, airlied@...ux.ie,
        daniel@...ll.ch, shawnguo@...nel.org, s.hauer@...gutronix.de,
        kernel@...gutronix.de, festevam@...il.com, tomi.valkeinen@...com,
        linux-imx@....com, dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH v3] 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: 45d59d704080 ("drm: Add new driver for MXSFB controller")
Signed-off-by: Stefan Agner <stefan@...er.ch>
Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
---
Changes in v3:
- Fix typo in commit message
- Add fixes tag

Changes in v2:
- Validate pitch in fb_create callback

 drivers/gpu/drm/mxsfb/mxsfb_drv.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/mxsfb/mxsfb_drv.c b/drivers/gpu/drm/mxsfb/mxsfb_drv.c
index 8c549c3931af..35122aef037b 100644
--- a/drivers/gpu/drm/mxsfb/mxsfb_drv.c
+++ b/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,
 };
-- 
2.28.0