[Intel-gfx] [PATCH 51/89] drm/i915/gen9: Add 2us read latency to WM level

[Damien Lespiau]

From: Vandana Kannan <vandana.kannan at intel.com>

According to the updated Bspec, The mailbox response data is not currently
accounting for memory read latency. Add 2 microseconds to the result for
each level.
This patch adds 2us to latency of level 0 for all cases and
for all other levels (1-7) only if latency[level] > 0.

v2: Slightly rework the patch and add a big comment (Damien)

Signed-off-by: Vandana Kannan <vandana.kannan at intel.com> (v1)
Signed-off-by: Damien Lespiau <damien.lespiau at intel.com>
Reviewed-by: M, Satheeshakrishna <satheeshakrishna.m at intel.com> (v1)
Cc: Lespiau, Damien <damien.lespiau at intel.com>
Cc: M, Satheeshakrishna <satheeshakrishna.m at intel.com>
---
 drivers/gpu/drm/i915/intel_pm.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 1e56067..16ad008 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -2254,6 +2254,7 @@ static void intel_read_wm_latency(struct drm_device *dev, uint16_t wm[8])
 	if (IS_GEN9(dev)) {
 		uint32_t val;
 		int ret;
+		int level, max_level = ilk_wm_max_level(dev);
 
 		/* read the first set of memory latencies[0:3] */
 		val = 0; /* data0 to be programmed to 0 for first set */
@@ -2267,6 +2268,7 @@ static void intel_read_wm_latency(struct drm_device *dev, uint16_t wm[8])
 			DRM_ERROR("SKL Mailbox read error = %d\n", ret);
 			return;
 		}
+
 		wm[0] = val & GEN9_MEM_LAT_LEVEL_MASK;
 		wm[1] = (val >> GEN9_MEM_LAT_LEVEL_1_5_SHIFT) &
 				GEN9_MEM_LAT_LEVEL_MASK;
@@ -2293,6 +2295,22 @@ static void intel_read_wm_latency(struct drm_device *dev, uint16_t wm[8])
 				GEN9_MEM_LAT_LEVEL_MASK;
 		wm[7] = (val >> GEN9_MEM_LAT_LEVEL_3_7_SHIFT) &
 				GEN9_MEM_LAT_LEVEL_MASK;
+
+		/*
+		 * punit doesn't take into account the read latency so we need
+		 * to add 2us to the various latency levels we retrieve from
+		 * the punit.
+		 *   - W0 is a bit special in that it's the only level that
+		 *   can't be disabled if we want to have display working, so
+		 *   we always add 2us there.
+		 *   - For levels >=1, punit returns 0us latency when they are
+		 *   disabled, so we respect that and don't add 2us then
+		 */
+		wm[0] += 2;
+		for (level = 1; level <= max_level; level++)
+			if (wm[level] != 0)
+				wm[level] += 2;
+
 	} else if (IS_HASWELL(dev) || IS_BROADWELL(dev)) {
 		uint64_t sskpd = I915_READ64(MCH_SSKPD);
 
-- 
1.8.3.1