[PATCH 5.5 148/189] drm/i915: Program MBUS with rmw during initialization

[Greg Kroah-Hartman]

From: Matt Roper <matthew.d.roper@xxxxxxxxx>

commit c725161924f9a5872a3e53b73345a6026a5c170e upstream.

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@xxxxxxxxx>
Signed-off-by: Matt Roper <matthew.d.roper@xxxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20200204011032.582737-1-matthew.d.roper@xxxxxxxxx
Reviewed-by: Matt Atwood <matthew.s.atwood@xxxxxxxxx>
(cherry picked from commit 837b63e6087838d0f1e612d448405419199d8033)
Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20200228004320.127142-1-matthew.d.roper@xxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/gpu/drm/i915/display/intel_display_power.c |   16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

--- a/drivers/gpu/drm/i915/display/intel_display_power.c
+++ b/drivers/gpu/drm/i915/display/intel_display_power.c
@@ -4471,13 +4471,19 @@ static void icl_dbuf_disable(struct drm_
 
 static void icl_mbus_init(struct drm_i915_private *dev_priv)
 {
-	u32 val;
+	u32 mask, val;
 
-	val = MBUS_ABOX_BT_CREDIT_POOL1(16) |
-	      MBUS_ABOX_BT_CREDIT_POOL2(16) |
-	      MBUS_ABOX_B_CREDIT(1) |
-	      MBUS_ABOX_BW_CREDIT(1);
+	mask = MBUS_ABOX_BT_CREDIT_POOL1_MASK |
+		MBUS_ABOX_BT_CREDIT_POOL2_MASK |
+		MBUS_ABOX_B_CREDIT_MASK |
+		MBUS_ABOX_BW_CREDIT_MASK;
 
+	val = I915_READ(MBUS_ABOX_CTL);
+	val &= ~mask;
+	val |= MBUS_ABOX_BT_CREDIT_POOL1(16) |
+		MBUS_ABOX_BT_CREDIT_POOL2(16) |
+		MBUS_ABOX_B_CREDIT(1) |
+		MBUS_ABOX_BW_CREDIT(1);
 	I915_WRITE(MBUS_ABOX_CTL, val);
 }