[RFC] drm/i915/display: Update vtotal math to address 32b build

[Lucas De Marchi]

On Wed, Jun 12, 2024 at 12:02:08AM GMT, Mitul Golani wrote:
>Fix few divisions which may not work on 32b builds.
>
>Use DIV_ROUND_UP, with that expecting deviate params
>from +/- 1 accuracy in value.
>
>Fixes: 1676ecd303ac ("drm/i915: Compute CMRR and calculate vtotal")
>Signed-off-by: Mitul Golani <mitulkumar.ajitkumar.golani at intel.com>
>---
> drivers/gpu/drm/i915/display/intel_vrr.c | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
>diff --git a/drivers/gpu/drm/i915/display/intel_vrr.c b/drivers/gpu/drm/i915/display/intel_vrr.c
>index 05f67dc9d98d..5112961f6964 100644
>--- a/drivers/gpu/drm/i915/display/intel_vrr.c
>+++ b/drivers/gpu/drm/i915/display/intel_vrr.c
>@@ -122,10 +122,11 @@ is_cmrr_frac_required(struct intel_crtc_state *crtc_state)
>
> 	actual_refresh_k =
> 		drm_mode_vrefresh(adjusted_mode) * FIXED_POINT_PRECISION;
>-	pixel_clock_per_line =
>-		adjusted_mode->crtc_clock * 1000 / adjusted_mode->crtc_htotal;
>+	pixel_clock_per_line = DIV_ROUND_UP(adjusted_mode->crtc_clock * 1000,
>+					    adjusted_mode->crtc_htotal);
> 	calculated_refresh_k =
>-		pixel_clock_per_line * FIXED_POINT_PRECISION / adjusted_mode->crtc_vtotal;
>+		DIV_ROUND_UP(pixel_clock_per_line * FIXED_POINT_PRECISION,
>+			     adjusted_mode->crtc_vtotal);
>
> 	if ((actual_refresh_k - calculated_refresh_k) < CMRR_PRECISION_TOLERANCE)
> 		return false;
>@@ -149,7 +150,8 @@ cmrr_get_vtotal(struct intel_crtc_state *crtc_state, bool video_mode_required)
>
> 	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;
>+	vtotal = DIV_ROUND_UP(adjusted_mode->crtc_clock * 1000 * multiplier_n,
>+			      crtc_state->cmrr.cmrr_n);

to fix the 32b build you need to build with DIV_ROUND_UP_ULL().

Lucas De Marchi

> 	adjusted_pixel_rate = adjusted_mode->crtc_clock * 1000 * multiplier_m;
> 	crtc_state->cmrr.cmrr_m = do_div(adjusted_pixel_rate, crtc_state->cmrr.cmrr_n);
>
>-- 
>2.45.2
>