[PATCH AUTOSEL 4.20 246/304] fbdev: fbmem: behave better with small rotated displays and many CPUs

[Sasha Levin]

From: Peter Rosin <peda at axentia.se>

[ Upstream commit f75df8d4b4fabfad7e3cba2debfad12741c6fde7 ]

Blitting an image with "negative" offsets is not working since there
is no clipping. It hopefully just crashes. For the bootup logo, there
is protection so that blitting does not happen as the image is drawn
further and further to the right (ROTATE_UR) or further and further
down (ROTATE_CW). There is however no protection when drawing in the
opposite directions (ROTATE_UD and ROTATE_CCW).

Add back this protection.

The regression is 20-odd years old but the mindless warning-killing
mentality displayed in commit 34bdb666f4b2 ("fbdev: fbmem: remove
positive test on unsigned values") is also to blame, methinks.

Fixes: 448d479747b8 ("fbdev: fb_do_show_logo() updates")
Signed-off-by: Peter Rosin <peda at axentia.se>
Cc: Tomi Valkeinen <tomi.valkeinen at ti.com>
Cc: Fabian Frederick <ffrederick at users.sourceforge.net>
Cc: Geert Uytterhoeven <geert+renesas at glider.be>
cc: Geoff Levand <geoff at infradead.org>
Cc: James Simmons <jsimmons at users.sf.net>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie at samsung.com>
Signed-off-by: Sasha Levin <sashal at kernel.org>
---
 drivers/video/fbdev/core/fbmem.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index 861bf8081619..7dd6924feaa8 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -436,7 +436,9 @@ static void fb_do_show_logo(struct fb_info *info, struct fb_image *image,
 			image->dx += image->width + 8;
 		}
 	} else if (rotate == FB_ROTATE_UD) {
-		for (x = 0; x < num; x++) {
+		u32 dx = image->dx;
+
+		for (x = 0; x < num && image->dx <= dx; x++) {
 			info->fbops->fb_imageblit(info, image);
 			image->dx -= image->width + 8;
 		}
@@ -448,7 +450,9 @@ static void fb_do_show_logo(struct fb_info *info, struct fb_image *image,
 			image->dy += image->height + 8;
 		}
 	} else if (rotate == FB_ROTATE_CCW) {
-		for (x = 0; x < num; x++) {
+		u32 dy = image->dy;
+
+		for (x = 0; x < num && image->dy <= dy; x++) {
 			info->fbops->fb_imageblit(info, image);
 			image->dy -= image->height + 8;
 		}
-- 
2.19.1