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

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

[Geert Uytterhoeven]

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@glider.be>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.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