drm/i915/kbl+: Enable IPC only for symmetric memory configurations

IPC may cause underflows if not used with dual channel symmetric
memory configuration. Disable IPC for non symmetric configurations in
affected platforms.
Display WA #1141

Changes Since V1:
 - Re-arrange the code.
 - update wrapper to return if memory is symmetric (Rodrigo)

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/20180824093225.12598-6-mahesh1.kumar@intel.com

drivers/gpu/drm/i915/i915_drv.c

@@ -1141,21 +1141,32 @@ skl_dram_get_channel_info(struct dram_channel_info *ch, u32 val)
 	return 0;
 }
 
+static bool
+intel_is_dram_symmetric(u32 val_ch0, u32 val_ch1,
+			struct dram_channel_info *ch0)
+{
+	return (val_ch0 == val_ch1 &&
+		(ch0->s_info.size == 0 ||
+		 (ch0->l_info.size == ch0->s_info.size &&
+		  ch0->l_info.width == ch0->s_info.width &&
+		  ch0->l_info.rank == ch0->s_info.rank)));
+}
+
 static int
 skl_dram_get_channels_info(struct drm_i915_private *dev_priv)
 {
 	struct dram_info *dram_info = &dev_priv->dram_info;
 	struct dram_channel_info ch0, ch1;
-	u32 val;
+	u32 val_ch0, val_ch1;
 	int ret;
 
-	val = I915_READ(SKL_MAD_DIMM_CH0_0_0_0_MCHBAR_MCMAIN);
-	ret = skl_dram_get_channel_info(&ch0, val);
+	val_ch0 = I915_READ(SKL_MAD_DIMM_CH0_0_0_0_MCHBAR_MCMAIN);
+	ret = skl_dram_get_channel_info(&ch0, val_ch0);
 	if (ret == 0)
 		dram_info->num_channels++;
 
-	val = I915_READ(SKL_MAD_DIMM_CH1_0_0_0_MCHBAR_MCMAIN);
-	ret = skl_dram_get_channel_info(&ch1, val);
+	val_ch1 = I915_READ(SKL_MAD_DIMM_CH1_0_0_0_MCHBAR_MCMAIN);
+	ret = skl_dram_get_channel_info(&ch1, val_ch1);
 	if (ret == 0)
 		dram_info->num_channels++;
 
@@ -1185,6 +1196,12 @@ skl_dram_get_channels_info(struct drm_i915_private *dev_priv)
 	if (ch0.is_16gb_dimm || ch1.is_16gb_dimm)
 		dram_info->is_16gb_dimm = true;
 
+	dev_priv->dram_info.symmetric_memory = intel_is_dram_symmetric(val_ch0,
+								       val_ch1,
+								       &ch0);
+
+	DRM_DEBUG_KMS("memory configuration is %sSymmetric memory\n",
+		      dev_priv->dram_info.symmetric_memory ? "" : "not ");
 	return 0;
 }