drm/i915: Simplify intel_cx0_program_phy_lane() with loop

It is possible to generalize the "disable" value for the transmitters to
be a bit mask based on the port width and the port reversal boolean,
with a small exception for DP-alt mode with "x1" port width.

Simplify the code by using such a mask and a for-loop instead of using
switch-case statements.

v2:
  - Use (i < 2) instead of (i / 2 == 0) for PHY lane mask selection.
    (Jani)

BSpec: 64539
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Gustavo Sousa <gustavo.sousa@intel.com>
Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230814131331.69516-3-gustavo.sousa@intel.com

drivers/gpu/drm/i915/display/intel_cx0_phy.c

@@ -2604,7 +2604,8 @@ static void intel_cx0_program_phy_lane(struct drm_i915_private *i915,
 				       struct intel_encoder *encoder, int lane_count,
 				       bool lane_reversal)
 {
-	u8 l0t1, l0t2, l1t1, l1t2;
+	int i;
+	u8 disables;
 	bool dp_alt_mode = intel_tc_port_in_dp_alt_mode(enc_to_dig_port(encoder));
 	enum port port = encoder->port;
 
@@ -2614,66 +2615,26 @@ static void intel_cx0_program_phy_lane(struct drm_i915_private *i915,
 			      C10_VDR_CTRL_MSGBUS_ACCESS,
 			      MB_WRITE_COMMITTED);
 
-	/* TODO: DP-alt MFD case where only one PHY lane should be programmed. */
-	l0t1 = intel_cx0_read(i915, port, INTEL_CX0_LANE0, PHY_CX0_TX_CONTROL(1, 2));
-	l0t2 = intel_cx0_read(i915, port, INTEL_CX0_LANE0, PHY_CX0_TX_CONTROL(2, 2));
-	l1t1 = intel_cx0_read(i915, port, INTEL_CX0_LANE1, PHY_CX0_TX_CONTROL(1, 2));
-	l1t2 = intel_cx0_read(i915, port, INTEL_CX0_LANE1, PHY_CX0_TX_CONTROL(2, 2));
-
-	l0t1 |= CONTROL2_DISABLE_SINGLE_TX;
-	l0t2 |= CONTROL2_DISABLE_SINGLE_TX;
-	l1t1 |= CONTROL2_DISABLE_SINGLE_TX;
-	l1t2 |= CONTROL2_DISABLE_SINGLE_TX;
-
-	if (lane_reversal) {
-		switch (lane_count) {
-		case 4:
-			l0t1 &= ~CONTROL2_DISABLE_SINGLE_TX;
-			fallthrough;
-		case 3:
-			l0t2 &= ~CONTROL2_DISABLE_SINGLE_TX;
-			fallthrough;
-		case 2:
-			l1t1 &= ~CONTROL2_DISABLE_SINGLE_TX;
-			fallthrough;
-		case 1:
-			l1t2 &= ~CONTROL2_DISABLE_SINGLE_TX;
-			break;
-		default:
-			MISSING_CASE(lane_count);
-		}
-	} else {
-		switch (lane_count) {
-		case 4:
-			l1t2 &= ~CONTROL2_DISABLE_SINGLE_TX;
-			fallthrough;
-		case 3:
-			l1t1 &= ~CONTROL2_DISABLE_SINGLE_TX;
-			fallthrough;
-		case 2:
-			l0t2 &= ~CONTROL2_DISABLE_SINGLE_TX;
-			l0t1 &= ~CONTROL2_DISABLE_SINGLE_TX;
-			break;
-		case 1:
-			if (dp_alt_mode)
-				l0t2 &= ~CONTROL2_DISABLE_SINGLE_TX;
-			else
-				l0t1 &= ~CONTROL2_DISABLE_SINGLE_TX;
-			break;
-		default:
-			MISSING_CASE(lane_count);
-		}
+	if (lane_reversal)
+		disables = REG_GENMASK8(3, 0) >> lane_count;
+	else
+		disables = REG_GENMASK8(3, 0) << lane_count;
+
+	if (dp_alt_mode && lane_count == 1) {
+		disables &= ~REG_GENMASK8(1, 0);
+		disables |= REG_FIELD_PREP8(REG_GENMASK8(1, 0), 0x1);
 	}
 
-	/* disable MLs */
-	intel_cx0_write(i915, port, INTEL_CX0_LANE0, PHY_CX0_TX_CONTROL(1, 2),
-			l0t1, MB_WRITE_COMMITTED);
-	intel_cx0_write(i915, port, INTEL_CX0_LANE0, PHY_CX0_TX_CONTROL(2, 2),
-			l0t2, MB_WRITE_COMMITTED);
-	intel_cx0_write(i915, port, INTEL_CX0_LANE1, PHY_CX0_TX_CONTROL(1, 2),
-			l1t1, MB_WRITE_COMMITTED);
-	intel_cx0_write(i915, port, INTEL_CX0_LANE1, PHY_CX0_TX_CONTROL(2, 2),
-			l1t2, MB_WRITE_COMMITTED);
+	/* TODO: DP-alt MFD case where only one PHY lane should be programmed. */
+	for (i = 0; i < 4; i++) {
+		int tx = i % 2 + 1;
+		u8 lane_mask = i < 2 ? INTEL_CX0_LANE0 : INTEL_CX0_LANE1;
+
+		intel_cx0_rmw(i915, port, lane_mask, PHY_CX0_TX_CONTROL(tx, 2),
+			      CONTROL2_DISABLE_SINGLE_TX,
+			      disables & BIT(i) ? CONTROL2_DISABLE_SINGLE_TX : 0,
+			      MB_WRITE_COMMITTED);
+	}
 
 	if (intel_is_c10phy(i915, intel_port_to_phy(i915, port)))
 		intel_cx0_rmw(i915, port, INTEL_CX0_BOTH_LANES,