drm/i915/dp: fix integer overflow in 128b/132b data rate calculation

The intermediate value 1000000 * 10 * 9671 overflows 32 bits, so force
promotion to a bigger type.

From the logs:

[drm:intel_dp_compute_config [i915]] DP link rate required 3657063 available -580783288

v2: Use mul_u32_u32() (Ville)

Fixes: 48efd014f0ea ("drm/i915/dp: add max data rate calculation for UHBR rates")
Cc: Manasi Navare <manasi.d.navare@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211026093407.11381-1-jani.nikula@intel.com

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index f5dc212..537c689 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -352,7 +352,7 @@ intel_dp_max_data_rate(int max_link_rate, int max_lanes)
                 */
                int max_link_rate_kbps = max_link_rate * 10;
 
-               max_link_rate_kbps = DIV_ROUND_CLOSEST_ULL(max_link_rate_kbps * 9671, 10000);
+               max_link_rate_kbps = DIV_ROUND_CLOSEST_ULL(mul_u32_u32(max_link_rate_kbps, 9671), 10000);
                max_link_rate = max_link_rate_kbps / 8;
        }