Re: [PATCH 3/3] drm/i915/display: Update calculation to avoid overflow

[Nautiyal, Ankit K]

On 6/12/2024 3:24 PM, Mitul Golani wrote:

Update calculation to avoid overflow.

Fixes: 1676ecd303ac ("drm/i915: Compute CMRR and calculate vtotal")
Cc: Mitul Golani <mitulkumar.ajitkumar.gol...@intel.com>
Cc: Ankit Nautiyal <ankit.k.nauti...@intel.com>
Cc: Suraj Kandpal <suraj.kand...@intel.com>
Cc: Jani Nikula <jani.nik...@linux.intel.com>
Cc: Stephen Rothwell <s...@canb.auug.org.au>

Signed-off-by: Mitul Golani <mitulkumar.ajitkumar.gol...@intel.com>

Reviewed-by: Ankit Nautiyal <ankit.k.nauti...@intel.com>

---
  drivers/gpu/drm/i915/display/intel_vrr.c | 9 +++++----
  1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_vrr.c 
b/drivers/gpu/drm/i915/display/intel_vrr.c
index dc9cf7ddafe9..5da9d5b9936e 100644
--- a/drivers/gpu/drm/i915/display/intel_vrr.c
+++ b/drivers/gpu/drm/i915/display/intel_vrr.c
@@ -147,10 +147,11 @@ cmrr_get_vtotal(struct intel_crtc_state *crtc_state, bool 
video_mode_required)
                multiplier_n = 1000;
        }

- crtc_state->cmrr.cmrr_n =

-               desired_refresh_rate * adjusted_mode->crtc_htotal * 
multiplier_n;
-       vtotal = (adjusted_mode->crtc_clock * 1000 * multiplier_n) / 
crtc_state->cmrr.cmrr_n;
-       adjusted_pixel_rate = adjusted_mode->crtc_clock * 1000 * multiplier_m;
+       crtc_state->cmrr.cmrr_n = mul_u32_u32(desired_refresh_rate * 
adjusted_mode->crtc_htotal,
+                                             multiplier_n);
+       vtotal = DIV_ROUND_UP_ULL(mul_u32_u32(adjusted_mode->crtc_clock * 1000, 
multiplier_n),
+                                 crtc_state->cmrr.cmrr_n);
+       adjusted_pixel_rate = mul_u32_u32(adjusted_mode->crtc_clock * 1000, 
multiplier_m);
        crtc_state->cmrr.cmrr_m = do_div(adjusted_pixel_rate, 
crtc_state->cmrr.cmrr_n);

return vtotal;