[Intel-gfx] [PATCH 1/2] drm/i915: Program MBUS with rmw during initialization

[Matt Roper]

It wasn't terribly clear from the bspec's wording, but after discussion
with the hardware folks, it turns out that we need to preserve the
pre-existing contents of the MBUS ABOX control register when
initializing a few specific bits.

Bspec: 49213
Bspec: 50096
Fixes: 4cb4585e5a7f ("drm/i915/icl: initialize MBus during display init")
Cc: Stanislav Lisovskiy <stanislav.lisovskiy at intel.com>
Signed-off-by: Matt Roper <matthew.d.roper at intel.com>
---
 drivers/gpu/drm/i915/display/intel_display_power.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_display_power.c b/drivers/gpu/drm/i915/display/intel_display_power.c
index 6d91e180db99..529319c962e8 100644
--- a/drivers/gpu/drm/i915/display/intel_display_power.c
+++ b/drivers/gpu/drm/i915/display/intel_display_power.c
@@ -4504,14 +4504,18 @@ static void icl_dbuf_disable(struct drm_i915_private *dev_priv)
 
 static void icl_mbus_init(struct drm_i915_private *dev_priv)
 {
-	u32 val;
+	u32 mask, val;
 
+	mask = MBUS_ABOX_BT_CREDIT_POOL1_MASK |
+		MBUS_ABOX_BT_CREDIT_POOL2_MASK |
+		MBUS_ABOX_B_CREDIT_MASK |
+		MBUS_ABOX_BW_CREDIT_MASK;
 	val = MBUS_ABOX_BT_CREDIT_POOL1(16) |
-	      MBUS_ABOX_BT_CREDIT_POOL2(16) |
-	      MBUS_ABOX_B_CREDIT(1) |
-	      MBUS_ABOX_BW_CREDIT(1);
+		MBUS_ABOX_BT_CREDIT_POOL2(16) |
+		MBUS_ABOX_B_CREDIT(1) |
+		MBUS_ABOX_BW_CREDIT(1);
 
-	intel_de_write(dev_priv, MBUS_ABOX_CTL, val);
+	intel_de_rmw(dev_priv, MBUS_ABOX_CTL, mask, val);
 }
 
 static void hsw_assert_cdclk(struct drm_i915_private *dev_priv)
-- 
2.24.1