From ce0cb93a5adb283f577cd4661f511047b5e39028 Mon Sep 17 00:00:00 2001
From: Colin Ian King <colin.king@canonical.com>
Date: Tue, 15 Sep 2020 17:20:49 +0100
Subject: drm/rockchip: cdn-dp: fix sign extension on an int multiply for a u64
 result
Git-commit: ce0cb93a5adb283f577cd4661f511047b5e39028
Patch-mainline: v5.14-rc1
References: bsc#1129770

The variable bit_per_pix is a u8 and is promoted in the multiplication
to an int type and then sign extended to a u64. If the result of the
int multiplication is greater than 0x7fffffff then the upper 32 bits will
be set to 1 as a result of the sign extension. Avoid this by casting
tu_size_reg to u64 to avoid sign extension and also a potential overflow.

Fixes: 1a0f7ed3abe2 ("drm/rockchip: cdn-dp: add cdn DP support for rk3399")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20200915162049.36434-1-colin.king@canonical.com
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
---
 drivers/gpu/drm/rockchip/cdn-dp-reg.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/gpu/drm/rockchip/cdn-dp-reg.c
+++ b/drivers/gpu/drm/rockchip/cdn-dp-reg.c
@@ -666,7 +666,7 @@ int cdn_dp_config_video(struct cdn_dp_de
 	 */
 	do {
 		tu_size_reg += 2;
-		symbol = tu_size_reg * mode->clock * bit_per_pix;
+		symbol = (u64)tu_size_reg * mode->clock * bit_per_pix;
 		do_div(symbol, dp->link.num_lanes * link_rate * 8);
 		rem = do_div(symbol, 1000);
 		if (tu_size_reg > 64) {