[Intel-gfx] [PATCH 1/1] drm/i915/adlp: Keep hardware default dbox B credits

[Yokoyama, Caz]

From: Caz Yokoyama <caz.yokoyama at intel.com>

Do not overwrite registers that don't need to change from default
value to 0.

bspec 49213
Cc: Radhakrishna Sripada <radhakrishna.sripada at intel.com>
Cc: José Roberto de Souza <jose.souza at intel.com>
Cc: Matt Roper <matthew.d.roper at intel.com>
Signed-off-by: Caz Yokoyama <caz.yokoyama at intel.com>
---
 drivers/gpu/drm/i915/display/intel_display.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
index a7ca38613f89..9190a3bc28a8 100644
--- a/drivers/gpu/drm/i915/display/intel_display.c
+++ b/drivers/gpu/drm/i915/display/intel_display.c
@@ -2955,18 +2955,23 @@ static void icl_pipe_mbus_enable(struct intel_crtc *crtc, bool joined_mbus)
 {
 	struct drm_i915_private *dev_priv = to_i915(crtc->base.dev);
 	enum pipe pipe = crtc->pipe;
-	u32 val;
+	u32 val = intel_de_read(dev_priv, PIPE_MBUS_DBOX_CTL(pipe));
 
+	val &= ~MBUS_DBOX_A_CREDIT_MASK;
 	/* Wa_22010947358:adl-p */
 	if (IS_ALDERLAKE_P(dev_priv))
-		val = joined_mbus ? MBUS_DBOX_A_CREDIT(6) : MBUS_DBOX_A_CREDIT(4);
+		val |= joined_mbus ? MBUS_DBOX_A_CREDIT(6) : MBUS_DBOX_A_CREDIT(4);
 	else
-		val = MBUS_DBOX_A_CREDIT(2);
+		val |= MBUS_DBOX_A_CREDIT(2);
 
-	if (DISPLAY_VER(dev_priv) >= 12) {
+	if (IS_ALDERLAKE_P(dev_priv)) {
+		/* Take effect hardware default MBUS_DBOX_B_CREDIT(8) */
+	} else if (DISPLAY_VER(dev_priv) >= 12) {
+		val &= ~(MBUS_DBOX_BW_CREDIT_MASK | MBUS_DBOX_B_CREDIT_MASK);
 		val |= MBUS_DBOX_BW_CREDIT(2);
 		val |= MBUS_DBOX_B_CREDIT(12);
 	} else {
+		val &= ~(MBUS_DBOX_BW_CREDIT_MASK | MBUS_DBOX_B_CREDIT_MASK);
 		val |= MBUS_DBOX_BW_CREDIT(1);
 		val |= MBUS_DBOX_B_CREDIT(8);
 	}
-- 
2.31.1.362.g311531c9de