[PATCH v3 4/5] drm/i915/scaler: Check if vblank is sufficient for scaler

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

Check if vblank is too short for scaler prefill latency.

--v2:
- Use hweight* family of functions for counting bits. [Jani]
- Update precision handling for hscale and vscale. [Ankit]
- Consider chroma downscaling factor during latency
calculation. [Ankit]
- Replace function name from scaler_prefill_time to
scaler_prefill_latency.

Signed-off-by: Mitul Golani <mitulkumar.ajitkumar.golani@intel.com>
---
 drivers/gpu/drm/i915/display/skl_watermark.c | 31 ++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/skl_watermark.c b/drivers/gpu/drm/i915/display/skl_watermark.c
index 29e8ea91c858..95f60819fe0a 100644
--- a/drivers/gpu/drm/i915/display/skl_watermark.c
+++ b/drivers/gpu/drm/i915/display/skl_watermark.c
@@ -2292,6 +2292,36 @@ static int icl_build_plane_wm(struct intel_crtc_state *crtc_state,
 	return 0;
 }
 
+static int
+scaler_prefill_latency(const struct intel_crtc_state *crtc_state)
+{
+	const struct intel_crtc_scaler_state *scaler_state =
+					&crtc_state->scaler_state;
+	int count = hweight32(scaler_state->scaler_users);
+	int latency;
+	long long  hscale_k =
+		mul_u32_u32(scaler_state->scalers[0].hscale, 1000);
+	long long vscale_k =
+		mul_u32_u32(scaler_state->scalers[0].vscale, 1000);
+
+	if (!count)
+		return 0;
+
+	if (count > 1) {
+		int chroma_downscaling_factor =
+			crtc_state->output_format == INTEL_OUTPUT_FORMAT_YCBCR444 ? 2 : 1;
+
+		latency = (4 * crtc_state->linetime) +
+			  (chroma_downscaling_factor *
+			   DIV_ROUND_UP_ULL((4 * crtc_state->linetime * hscale_k * vscale_k),
+					    USHRT_MAX));
+	} else {
+		latency = 4 * crtc_state->linetime;
+	}
+
+	return latency;
+}
+
 static bool
 skl_is_vblank_too_short(const struct intel_crtc_state *crtc_state,
 			int wm0_lines, int latency)
@@ -2302,6 +2332,7 @@ skl_is_vblank_too_short(const struct intel_crtc_state *crtc_state,
 	/* FIXME missing scaler and DSC pre-fill time */
 	return crtc_state->framestart_delay +
 		intel_usecs_to_scanlines(adjusted_mode, latency) +
+		scaler_prefill_latency(crtc_state) +
 		wm0_lines >
 		adjusted_mode->crtc_vtotal - adjusted_mode->crtc_vblank_start;
 }
-- 
2.46.0