linux-kernel - [PATCH 5.10 519/663] drm/modes: Switch to 64bit maths to avoid integer overflow

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Date:   Mon,  1 Mar 2021 17:12:47 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Randy Dunlap <rdunlap@...radead.org>,
        Ville Syrjälä 
        <ville.syrjala@...ux.intel.com>,
        Chris Wilson <chris@...is-wilson.co.uk>
Subject: [PATCH 5.10 519/663] drm/modes: Switch to 64bit maths to avoid integer overflow

From: Ville Syrjälä <ville.syrjala@...ux.intel.com>

commit 5b34ab52401f0f1f191bcb83a182c83b506f4763 upstream.

The new >8k CEA modes have dotclocks reaching 5.94 GHz, which
means our clock*1000 will now overflow the 32bit unsigned
integer. Switch to 64bit maths to avoid it.

Cc: stable@...r.kernel.org
Reported-by: Randy Dunlap <rdunlap@...radead.org>
Signed-off-by: Ville Syrjälä <ville.syrjala@...ux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201022194256.30978-1-ville.syrjala@linux.intel.com
Tested-by: Randy Dunlap <rdunlap@...radead.org>
Reviewed-by: Chris Wilson <chris@...is-wilson.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/gpu/drm/drm_modes.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/gpu/drm/drm_modes.c
+++ b/drivers/gpu/drm/drm_modes.c
@@ -762,7 +762,7 @@ int drm_mode_vrefresh(const struct drm_d
 	if (mode->htotal == 0 || mode->vtotal == 0)
 		return 0;
 
-	num = mode->clock * 1000;
+	num = mode->clock;
 	den = mode->htotal * mode->vtotal;
 
 	if (mode->flags & DRM_MODE_FLAG_INTERLACE)
@@ -772,7 +772,7 @@ int drm_mode_vrefresh(const struct drm_d
 	if (mode->vscan > 1)
 		den *= mode->vscan;
 
-	return DIV_ROUND_CLOSEST(num, den);
+	return DIV_ROUND_CLOSEST_ULL(mul_u32_u32(num, 1000), den);
 }
 EXPORT_SYMBOL(drm_mode_vrefresh);