[Intel-gfx] [PATCH] drm/i915/chv: Recomputing CHV watermark.

[abhay.kumar at intel.com]

From: Abhay <abhay.kumar at intel.com>

Current WM calculation is causing regression on SR residency.
Recomputing WM using new formula as provided by VPG

Change-Id: I9dbd6a7b70c84454748dee41738130934230b763
Signed-off-by: Abhay <abhay.kumar at intel.com>
---
 drivers/gpu/drm/i915/intel_pm.c | 26 +++++++++++++++-----------
 1 file changed, 15 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index a960cdd..01a5d79 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -1546,6 +1546,13 @@ static int vlv_compute_wm(struct intel_crtc *crtc,
 			  int fifo_size)
 {
 	int clock, entries, pixel_size;
+	uint32_t line_time = 0,buffer_wm = 0;
+
+	/* using memory DVFS latency of 23usec */
+	int latency = 23000;
+
+	int htotal = crtc->config.adjusted_mode.crtc_htotal;
+	int hdisplay = to_intel_crtc(crtc)->config.pipe_src_w;
 
 	/*
 	 * FIXME the plane might have an fb
@@ -1557,18 +1564,15 @@ static int vlv_compute_wm(struct intel_crtc *crtc,
 	pixel_size = drm_format_plane_cpp(plane->base.fb->pixel_format, 0);
 	clock = crtc->config.adjusted_mode.crtc_clock;
 
-	entries = DIV_ROUND_UP(clock, 1000) * pixel_size;
+	line_time = max(htotal * 1000 / clock, 1);
+
+	/* Max FIFO size */
+	fifo_size = 96 * 1024;
+
+	buffer_wm = (fifo_size -  (((latency /line_time /1000) + 1 ) *
+							hdisplay * pixel_size));
+	return buffer_wm;
 
-	/*
-	 * Set up the watermark such that we don't start issuing memory
-	 * requests until we are within PND's max deadline value (256us).
-	 * Idea being to be idle as long as possible while still taking
-	 * advatange of PND's deadline scheduling. The limit of 8
-	 * cachelines (used when the FIFO will anyway drain in less time
-	 * than 256us) should match what we would be done if trickle
-	 * feed were enabled.
-	 */
-	return fifo_size - clamp(DIV_ROUND_UP(256 * entries, 64), 0, fifo_size - 8);
 }
 
 static bool vlv_compute_sr_wm(struct drm_device *dev,
-- 
2.1.4