drm/i915: Implement 16GB dimm wa for latency level-0

Memory with 16GB dimms require an increase of 1us in level-0 latency.
This patch implements the same.
Bspec: 4381

changes since V1:
 - s/memdev_info/dram_info
 - make skl_is_16gb_dimm pure function
Changes since V2:
 - make is_16gb_dimm more generic
 - rebase
Changes since V3:
 - Simplify condition (Maarten)

Signed-off-by: Mahesh Kumar <mahesh1.kumar@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180831110942.9234-1-mahesh1.kumar@intel.com

drivers/gpu/drm/i915/i915_drv.c

@@ -1075,6 +1075,21 @@ static enum dram_rank skl_get_dimm_rank(u8 size, u32 rank)
 	return I915_DRAM_RANK_INVALID;
 }
 
+static bool
+skl_is_16gb_dimm(enum dram_rank rank, u8 size, u8 width)
+{
+	if (rank == I915_DRAM_RANK_SINGLE && width == 8 && size == 16)
+		return true;
+	else if (rank == I915_DRAM_RANK_DUAL && width == 8 && size == 32)
+		return true;
+	else if (rank == SKL_DRAM_RANK_SINGLE && width == 16 && size == 8)
+		return true;
+	else if (rank == SKL_DRAM_RANK_DUAL && width == 16 && size == 16)
+		return true;
+
+	return false;
+}
+
 static int
 skl_dram_get_channel_info(struct dram_channel_info *ch, u32 val)
 {
@@ -1112,6 +1127,11 @@ skl_dram_get_channel_info(struct dram_channel_info *ch, u32 val)
 	else
 		ch->rank = I915_DRAM_RANK_SINGLE;
 
+	ch->is_16gb_dimm = skl_is_16gb_dimm(ch->l_info.rank, ch->l_info.size,
+					    ch->l_info.width) ||
+			   skl_is_16gb_dimm(ch->s_info.rank, ch->s_info.size,
+					    ch->s_info.width);
+
 	DRM_DEBUG_KMS("(size:width:rank) L(%dGB:X%d:%s) S(%dGB:X%d:%s)\n",
 		      ch->l_info.size, ch->l_info.width,
 		      ch->l_info.rank ? "dual" : "single",
@@ -1144,6 +1164,8 @@ skl_dram_get_channels_info(struct drm_i915_private *dev_priv)
 		return -EINVAL;
 	}
 
+	dram_info->valid_dimm = true;
+
 	/*
 	 * If any of the channel is single rank channel, worst case output
 	 * will be same as if single rank memory, so consider single rank
@@ -1159,6 +1181,10 @@ skl_dram_get_channels_info(struct drm_i915_private *dev_priv)
 		DRM_INFO("couldn't get memory rank information\n");
 		return -EINVAL;
 	}
+
+	if (ch0.is_16gb_dimm || ch1.is_16gb_dimm)
+		dram_info->is_16gb_dimm = true;
+
 	return 0;
 }
 
@@ -1271,6 +1297,7 @@ bxt_get_dram_info(struct drm_i915_private *dev_priv)
 		return -EINVAL;
 	}
 
+	dram_info->valid_dimm = true;
 	dram_info->valid = true;
 	return 0;
 }
@@ -1283,6 +1310,8 @@ intel_get_dram_info(struct drm_i915_private *dev_priv)
 	int ret;
 
 	dram_info->valid = false;
+	dram_info->valid_dimm = false;
+	dram_info->is_16gb_dimm = false;
 	dram_info->rank = I915_DRAM_RANK_INVALID;
 	dram_info->bandwidth_kbps = 0;
 	dram_info->num_channels = 0;
@@ -1306,9 +1335,9 @@ intel_get_dram_info(struct drm_i915_private *dev_priv)
 		sprintf(bandwidth_str, "unknown");
 	DRM_DEBUG_KMS("DRAM bandwidth:%s, total-channels: %u\n",
 		      bandwidth_str, dram_info->num_channels);
-	DRM_DEBUG_KMS("DRAM rank: %s rank\n",
+	DRM_DEBUG_KMS("DRAM rank: %s rank 16GB-dimm:%s\n",
 		      (dram_info->rank == I915_DRAM_RANK_DUAL) ?
-		      "dual" : "single");
+		      "dual" : "single", yesno(dram_info->is_16gb_dimm));
 }
 
 /**

drivers/gpu/drm/i915/i915_drv.h

@@ -1947,6 +1947,8 @@ struct drm_i915_private {
 
 	struct dram_info {
 		bool valid;
+		bool valid_dimm;
+		bool is_16gb_dimm;
 		u8 num_channels;
 		enum dram_rank {
 			I915_DRAM_RANK_INVALID = 0,
@@ -2175,6 +2177,7 @@ struct dram_channel_info {
 		enum dram_rank rank;
 	} l_info, s_info;
 	enum dram_rank rank;
+	bool is_16gb_dimm;
 };
 
 static inline struct drm_i915_private *to_i915(const struct drm_device *dev)

drivers/gpu/drm/i915/intel_pm.c

@@ -2875,6 +2875,16 @@ static void intel_read_wm_latency(struct drm_i915_private *dev_priv,
 			}
 		}
 
+		/*
+		 * WA Level-0 adjustment for 16GB DIMMs: SKL+
+		 * If we could not get dimm info enable this WA to prevent from
+		 * any underrun. If not able to get Dimm info assume 16GB dimm
+		 * to avoid any underrun.
+		 */
+		if (!dev_priv->dram_info.valid_dimm ||
+		    dev_priv->dram_info.is_16gb_dimm)
+			wm[0] += 1;
+
 	} else if (IS_HASWELL(dev_priv) || IS_BROADWELL(dev_priv)) {
 		uint64_t sskpd = I915_READ64(MCH_SSKPD);