[Intel-gfx] [PATCH 2/2] drm/i915/intel_cdclk: Add vdsc with bigjoiner constraints on min_cdlck

[Ankit Nautiyal]

As per Bsepc:49259, Bigjoiner BW check puts restriction on the
compressed bpp for a given CDCLK, pixelclock in cases where
Bigjoiner + DSC are used.

Currently compressed bpp is computed first, and it is ensured that
the bpp will work at least with the max CDCLK freq.

Since the CDCLK is computed later, lets account for Bigjoiner BW
check while calculating Min CDCLK.

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal at intel.com>
---
 drivers/gpu/drm/i915/display/intel_cdclk.c | 49 ++++++++++++++++++----
 1 file changed, 42 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_cdclk.c b/drivers/gpu/drm/i915/display/intel_cdclk.c
index 084a483f9776..4c0e0d605bf1 100644
--- a/drivers/gpu/drm/i915/display/intel_cdclk.c
+++ b/drivers/gpu/drm/i915/display/intel_cdclk.c
@@ -2400,6 +2400,46 @@ static int intel_planes_min_cdclk(const struct intel_crtc_state *crtc_state)
 	return min_cdclk;
 }
 
+static int intel_vdsc_min_cdclk(const struct intel_crtc_state *crtc_state)
+{
+	struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
+	struct drm_i915_private *i915 = to_i915(crtc->base.dev);
+	int min_cdclk = 0;
+
+	/*
+	 * When we decide to use only one VDSC engine, since
+	 * each VDSC operates with 1 ppc throughput, pixel clock
+	 * cannot be higher than the VDSC clock (cdclk)
+	 */
+	if (!crtc_state->dsc.dsc_split)
+		min_cdclk = max(min_cdclk, (int)crtc_state->pixel_rate);
+
+	if (crtc_state->bigjoiner_pipes) {
+		/*
+		 * According to Bigjoiner bw check:
+		 * compressed_bpp <= PPC * CDCLK * Big joiner Interface bits / Pixel clock
+		 *
+		 * We have already computed compressed_bpp, so now compute the min CDCLK that
+		 * is required to support this compressed_bpp.
+		 *
+		 * => CDCLK >= compressed_bpp * Pixel clock / (PPC * Bigjoiner Interface bits)
+		 *
+		 * Since Num of pipes joined = 2, and PPC = 2 with bigjoiner
+		 * => CDCLK >= compressed_bpp * pixel_rate  / Bigjoiner Interface bits
+		 *
+		 * #TODO Bspec mentions to account for FEC overhead while using pixel clock.
+		 * Check if we need to use FEC overhead in the above calculations.
+		 */
+		int bigjoiner_interface_bits = DISPLAY_VER(i915) > 13 ? 36 : 24;
+		int min_cdclk_bj = crtc_state->dsc.compressed_bpp * crtc_state->pixel_rate /
+				   bigjoiner_interface_bits;
+
+		min_cdclk = max(min_cdclk, min_cdclk_bj);
+	}
+
+	return min_cdclk;
+}
+
 int intel_crtc_compute_min_cdclk(const struct intel_crtc_state *crtc_state)
 {
 	struct drm_i915_private *dev_priv =
@@ -2471,13 +2511,8 @@ int intel_crtc_compute_min_cdclk(const struct intel_crtc_state *crtc_state)
 	/* Account for additional needs from the planes */
 	min_cdclk = max(intel_planes_min_cdclk(crtc_state), min_cdclk);
 
-	/*
-	 * When we decide to use only one VDSC engine, since
-	 * each VDSC operates with 1 ppc throughput, pixel clock
-	 * cannot be higher than the VDSC clock (cdclk)
-	 */
-	if (crtc_state->dsc.compression_enable && !crtc_state->dsc.dsc_split)
-		min_cdclk = max(min_cdclk, (int)crtc_state->pixel_rate);
+	if (crtc_state->dsc.compression_enable)
+		min_cdclk = max(min_cdclk, intel_vdsc_min_cdclk(crtc_state));
 
 	/*
 	 * HACK. Currently for TGL/DG2 platforms we calculate
-- 
2.25.1