linux-kernel - [PATCH v2] drm/bridge: nwl-dsi: Avoid potential multiplication overflow on 32-bit

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Date:   Wed, 14 Jul 2021 11:48:06 +0200
From:   Geert Uytterhoeven <geert+renesas@...der.be>
To:     Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Robert Foss <robert.foss@...aro.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Fabio Estevam <festevam@...il.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Subject: [PATCH v2] drm/bridge: nwl-dsi: Avoid potential multiplication overflow on 32-bit

As nwl_dsi.lanes is u32, and NSEC_PER_SEC is 1000000000L, the second
multiplication in

    dsi->lanes * 8 * NSEC_PER_SEC

will overflow on a 32-bit platform.  Fix this by making the constant
unsigned long long, forcing 64-bit arithmetic.

As iMX8 is arm64, this driver is currently used on 64-bit platforms
only, where long is 64-bit, so this cannot happen.  But the issue will
start to happen when the driver is reused for a 32-bit SoC (e.g.
i.MX7ULP), or when code is copied for a new driver.

Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
Reviewed-by: Fabio Estevam <festevam@...il.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
---
Compile-tested only.

v2:
  - Add Reviewed-by,
  - Add reference to i.MX7ULP.
---
 drivers/gpu/drm/bridge/nwl-dsi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/bridge/nwl-dsi.c b/drivers/gpu/drm/bridge/nwl-dsi.c
index 873995f0a7416e58..6002404ffcb9df08 100644
--- a/drivers/gpu/drm/bridge/nwl-dsi.c
+++ b/drivers/gpu/drm/bridge/nwl-dsi.c
@@ -196,7 +196,7 @@ static u32 ps2bc(struct nwl_dsi *dsi, unsigned long long ps)
 	u32 bpp = mipi_dsi_pixel_format_to_bpp(dsi->format);
 
 	return DIV64_U64_ROUND_UP(ps * dsi->mode.clock * bpp,
-				  dsi->lanes * 8 * NSEC_PER_SEC);
+				  dsi->lanes * 8ULL * NSEC_PER_SEC);
 }
 
 /*
-- 
2.25.1