Re: [PATCH 03/15] drm/i915/skl_watermark: Pass linetime as argument to latency helpers

[Nautiyal, Ankit K]

On 9/11/2025 7:28 PM, Ville Syrjälä wrote:
On Thu, Sep 11, 2025 at 08:15:42AM +0530, Ankit Nautiyal wrote:
Refactor dsc_prefill_latency and scaler_prefill_latency to take
linetime as an explicit parameter instead of computing it internally.

This avoids redundant calculations and simplifies scanline conversion
logic in skl_is_vblank_too_short().

This change also facilitates future extraction of these helpers for use
cases where latencies are computed for an optimized guardband, based on the
highest resolution mode, rather than the current mode.

Signed-off-by: Ankit Nautiyal <ankit.k.nauti...@intel.com>
Reviewed-by: Mitul Golani <mitulkumar.ajitkumar.gol...@intel.com>
---
  drivers/gpu/drm/i915/display/skl_watermark.c | 18 ++++++++----------
  1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/skl_watermark.c 
b/drivers/gpu/drm/i915/display/skl_watermark.c
index 51548447f4aa..49d424f5b305 100644
--- a/drivers/gpu/drm/i915/display/skl_watermark.c
+++ b/drivers/gpu/drm/i915/display/skl_watermark.c
@@ -2176,13 +2176,11 @@ cdclk_prefill_adjustment(const struct intel_crtc_state 
*crtc_state)
  }
  
  static int
-dsc_prefill_latency(const struct intel_crtc_state *crtc_state)
+dsc_prefill_latency(const struct intel_crtc_state *crtc_state, int linetime)
  {
        struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
        const struct intel_crtc_scaler_state *scaler_state =
                                        &crtc_state->scaler_state;
-       int linetime = DIV_ROUND_UP(1000 * crtc_state->hw.adjusted_mode.htotal,
-                                   crtc_state->hw.adjusted_mode.clock);
        int num_scaler_users = hweight32(scaler_state->scaler_users);
        int chroma_downscaling_factor =
                crtc_state->output_format == INTEL_OUTPUT_FORMAT_YCBCR420 ? 4 : 
1;
@@ -2206,18 +2204,16 @@ dsc_prefill_latency(const struct intel_crtc_state 
*crtc_state)
  
  	dsc_prefill_latency *= cdclk_prefill_adjustment(crtc_state);
  
-	return intel_usecs_to_scanlines(&crtc_state->hw.adjusted_mode, dsc_prefill_latency);
+       return dsc_prefill_latency;
  }
  
  static int
-scaler_prefill_latency(const struct intel_crtc_state *crtc_state)
+scaler_prefill_latency(const struct intel_crtc_state *crtc_state, int linetime)
  {
        const struct intel_crtc_scaler_state *scaler_state =
                                        &crtc_state->scaler_state;
        int num_scaler_users = hweight32(scaler_state->scaler_users);
        int scaler_prefill_latency = 0;
-       int linetime = DIV_ROUND_UP(1000 * crtc_state->hw.adjusted_mode.htotal,
-                                   crtc_state->hw.adjusted_mode.clock);
  
  	if (!num_scaler_users)
                return scaler_prefill_latency;
@@ -2238,7 +2234,7 @@ scaler_prefill_latency(const struct intel_crtc_state 
*crtc_state)
  
  	scaler_prefill_latency *= cdclk_prefill_adjustment(crtc_state);
  
-	return intel_usecs_to_scanlines(&crtc_state->hw.adjusted_mode, scaler_prefill_latency);
+       return scaler_prefill_latency;
  }
  
  static bool
@@ -2247,11 +2243,13 @@ skl_is_vblank_too_short(const struct intel_crtc_state 
*crtc_state,
  {
        const struct drm_display_mode *adjusted_mode =
                &crtc_state->hw.adjusted_mode;
+       int linetime = DIV_ROUND_UP(1000 * adjusted_mode->htotal,
+                                   adjusted_mode->clock);
  
  	return crtc_state->framestart_delay +
                intel_usecs_to_scanlines(adjusted_mode, latency) +
-               scaler_prefill_latency(crtc_state) +
-               dsc_prefill_latency(crtc_state) +
+               DIV_ROUND_UP(scaler_prefill_latency(crtc_state, linetime), 
linetime) +
+               DIV_ROUND_UP(dsc_prefill_latency(crtc_state, linetime), 
linetime) +
Looks like you could just add up all the usec latency numbers and
convert the whole thing with a single intel_usecs_to_scanlines() call
instead of this mismash of hand rolled and non-hand rolled stuff.

Hmm.. sure can use intel_usecs_to_scanlines() here. Will change this in 
next revision.


Regards,

Ankit

                wm0_lines >
                adjusted_mode->crtc_vtotal - adjusted_mode->crtc_vblank_start;
  }
--
2.45.2