[Intel-gfx] [PATCH V2 5/5] drm/i915/kbl+: Enable IPC only for symmetric memory configurations

[Mahesh Kumar]

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 at intel.com>
---
 drivers/gpu/drm/i915/i915_drv.c | 27 ++++++++++++++++++++++-----
 drivers/gpu/drm/i915/i915_drv.h |  1 +
 drivers/gpu/drm/i915/intel_pm.c |  5 +++++
 3 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 2bc74c01a0e5..61d756ae7bf0 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -1154,21 +1154,32 @@ 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++;
 
@@ -1198,6 +1209,12 @@ 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;
 }
 
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 6c432684c721..e7faa046f78a 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1955,6 +1955,7 @@ struct drm_i915_private {
 			I915_DRAM_RANK_DUAL
 		} rank;
 		u32 bandwidth_kbps;
+		bool symmetric_memory;
 	} dram_info;
 
 	struct i915_runtime_pm runtime_pm;
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 77970e38d939..c27646fb4cec 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -6124,6 +6124,11 @@ void intel_enable_ipc(struct drm_i915_private *dev_priv)
 	if (IS_SKYLAKE(dev_priv))
 		dev_priv->ipc_enabled = false;
 
+	/* Display WA #1141: SKL:all KBL:all CFL */
+	if ((IS_KABYLAKE(dev_priv) || IS_COFFEELAKE(dev_priv)) &&
+	    !dev_priv->dram_info.symmetric_memory)
+		dev_priv->ipc_enabled = false;
+
 	val = I915_READ(DISP_ARB_CTL2);
 
 	if (dev_priv->ipc_enabled)
-- 
2.16.2