[RFC v1 2/4] drm/i915/watermark: Add WM0 prefill latency

[Mitul Golani <mitulkumar.ajitkumar.golani@intel.com>]

Calculate WM0 prefill latency which accounts for maximum time
to fill data buffer up to watermark 0.

Signed-off-by: Mitul Golani <mitulkumar.ajitkumar.golani@intel.com>
---
 drivers/gpu/drm/i915/display/skl_watermark.c | 21 ++++++++++++++++++++
 drivers/gpu/drm/i915/display/skl_watermark.h |  1 +
 2 files changed, 22 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/skl_watermark.c b/drivers/gpu/drm/i915/display/skl_watermark.c
index d3bbf335c749..8afa24943333 100644
--- a/drivers/gpu/drm/i915/display/skl_watermark.c
+++ b/drivers/gpu/drm/i915/display/skl_watermark.c
@@ -2260,6 +2260,27 @@ static int skl_max_wm0_lines(const struct intel_crtc_state *crtc_state)
 	return wm0_lines;
 }
 
+int skl_calc_wm0_prefill_latency(struct intel_crtc_state *crtc_state)
+{
+	struct intel_display *display = to_intel_display(crtc_state);
+	int cdclk_prefill_latency, wm0_prefill_latency;
+	int linetime =
+		DIV_ROUND_UP(crtc_state->hw.adjusted_mode.htotal * 1000,
+			     crtc_state->hw.adjusted_mode.crtc_clock);
+	/*
+	 * TODO: DIV_ROUND_UP will also round off to 1, so need to
+	 * check upon if this can be eliminated here
+	 */
+	cdclk_prefill_latency =
+		MIN(1, DIV_ROUND_UP(crtc_state->pixel_rate,
+				    2 * display->cdclk.hw.cdclk));
+	wm0_prefill_latency =
+		20 + (linetime * skl_max_wm0_lines(crtc_state) * cdclk_prefill_latency);
+
+	return intel_usecs_to_scanlines(&crtc_state->hw.adjusted_mode,
+									wm0_prefill_latency);
+}
+
 static int skl_max_wm_level_for_vblank(struct intel_crtc_state *crtc_state,
 				       int wm0_lines)
 {
diff --git a/drivers/gpu/drm/i915/display/skl_watermark.h b/drivers/gpu/drm/i915/display/skl_watermark.h
index e73baec94873..9495a142fbe5 100644
--- a/drivers/gpu/drm/i915/display/skl_watermark.h
+++ b/drivers/gpu/drm/i915/display/skl_watermark.h
@@ -23,6 +23,7 @@ struct skl_wm_level;
 
 u8 intel_enabled_dbuf_slices_mask(struct drm_i915_private *i915);
 
+int skl_calc_wm0_prefill_latency(struct intel_crtc_state *crtc_state);
 void intel_sagv_pre_plane_update(struct intel_atomic_state *state);
 void intel_sagv_post_plane_update(struct intel_atomic_state *state);
 bool intel_can_enable_sagv(struct drm_i915_private *i915,
-- 
2.46.0