drm/i915/cnl: Fix RMW on ddi vswing sequence.

Paulo noticed that we were missing few bits clear
before writing values back to the register on
these RMW MMIO operations.

v2: Remove "POST_" from CURSOR_COEFF_MASK. (Paulo).
v3: Remove unnecessary braces. (Jani).

Fixes: cf54ca8bc567 ("drm/i915/cnl: Implement voltage swing sequence.")
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Manasi Navare <manasi.d.navare@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1497897572-22520-1-git-send-email-rodrigo.vivi@intel.com

drivers/gpu/drm/i915/i915_reg.h

@@ -1764,8 +1764,11 @@ enum skl_disp_power_wells {
 						    _CNL_PORT_TX_DW2_LN0_AE, \
 						    _CNL_PORT_TX_DW2_LN0_F)
 #define   SWING_SEL_UPPER(x)		((x >> 3) << 15)
+#define   SWING_SEL_UPPER_MASK		(1 << 15)
 #define   SWING_SEL_LOWER(x)		((x & 0x7) << 11)
+#define   SWING_SEL_LOWER_MASK		(0x7 << 11)
 #define   RCOMP_SCALAR(x)		((x) << 0)
+#define   RCOMP_SCALAR_MASK		(0xFF << 0)
 
 #define _CNL_PORT_TX_DW4_GRP_AE		0x162350
 #define _CNL_PORT_TX_DW4_GRP_B		0x1623D0
@@ -1795,8 +1798,11 @@ enum skl_disp_power_wells {
 						    _CNL_PORT_TX_DW4_LN0_F)
 #define   LOADGEN_SELECT		(1 << 31)
 #define   POST_CURSOR_1(x)		((x) << 12)
+#define   POST_CURSOR_1_MASK		(0x3F << 12)
 #define   POST_CURSOR_2(x)		((x) << 6)
+#define   POST_CURSOR_2_MASK		(0x3F << 6)
 #define   CURSOR_COEFF(x)		((x) << 0)
+#define   CURSOR_COEFF_MASK		(0x3F << 6)
 
 #define _CNL_PORT_TX_DW5_GRP_AE		0x162354
 #define _CNL_PORT_TX_DW5_GRP_B		0x1623D4
@@ -1825,7 +1831,9 @@ enum skl_disp_power_wells {
 #define   TX_TRAINING_EN		(1 << 31)
 #define   TAP3_DISABLE			(1 << 29)
 #define   SCALING_MODE_SEL(x)		((x) << 18)
+#define   SCALING_MODE_SEL_MASK		(0x7 << 18)
 #define   RTERM_SELECT(x)		((x) << 3)
+#define   RTERM_SELECT_MASK		(0x7 << 3)
 
 #define _CNL_PORT_TX_DW7_GRP_AE		0x16235C
 #define _CNL_PORT_TX_DW7_GRP_B		0x1623DC
@@ -1852,6 +1860,7 @@ enum skl_disp_power_wells {
 						    _CNL_PORT_TX_DW7_LN0_AE, \
 						    _CNL_PORT_TX_DW7_LN0_F)
 #define   N_SCALAR(x)			((x) << 24)
+#define   N_SCALAR_MASK			(0x7F << 24)
 
 /* The spec defines this only for BXT PHY0, but lets assume that this
  * would exist for PHY1 too if it had a second channel.

drivers/gpu/drm/i915/intel_ddi.c

@@ -1813,11 +1813,14 @@ static void cnl_ddi_vswing_program(struct drm_i915_private *dev_priv,
 
 	/* Set PORT_TX_DW5 Scaling Mode Sel to 010b. */
 	val = I915_READ(CNL_PORT_TX_DW5_LN0(port));
+	val &= ~SCALING_MODE_SEL_MASK;
 	val |= SCALING_MODE_SEL(2);
 	I915_WRITE(CNL_PORT_TX_DW5_GRP(port), val);
 
 	/* Program PORT_TX_DW2 */
 	val = I915_READ(CNL_PORT_TX_DW2_LN0(port));
+	val &= ~(SWING_SEL_LOWER_MASK | SWING_SEL_UPPER_MASK |
+		 RCOMP_SCALAR_MASK);
 	val |= SWING_SEL_UPPER(ddi_translations[level].dw2_swing_sel);
 	val |= SWING_SEL_LOWER(ddi_translations[level].dw2_swing_sel);
 	/* Rcomp scalar is fixed as 0x98 for every table entry */
@@ -1828,6 +1831,8 @@ static void cnl_ddi_vswing_program(struct drm_i915_private *dev_priv,
 	/* We cannot write to GRP. It would overrite individual loadgen */
 	for (ln = 0; ln < 4; ln++) {
 		val = I915_READ(CNL_PORT_TX_DW4_LN(port, ln));
+		val &= ~(POST_CURSOR_1_MASK | POST_CURSOR_2_MASK |
+			 CURSOR_COEFF_MASK);
 		val |= POST_CURSOR_1(ddi_translations[level].dw4_post_cursor_1);
 		val |= POST_CURSOR_2(ddi_translations[level].dw4_post_cursor_2);
 		val |= CURSOR_COEFF(ddi_translations[level].dw4_cursor_coeff);
@@ -1837,12 +1842,14 @@ static void cnl_ddi_vswing_program(struct drm_i915_private *dev_priv,
         /* Program PORT_TX_DW5 */
 	/* All DW5 values are fixed for every table entry */
 	val = I915_READ(CNL_PORT_TX_DW5_LN0(port));
+	val &= ~RTERM_SELECT_MASK;
 	val |= RTERM_SELECT(6);
 	val |= TAP3_DISABLE;
 	I915_WRITE(CNL_PORT_TX_DW5_GRP(port), val);
 
         /* Program PORT_TX_DW7 */
 	val = I915_READ(CNL_PORT_TX_DW7_LN0(port));
+	val &= ~N_SCALAR_MASK;
 	val |= N_SCALAR(ddi_translations[level].dw7_n_scalar);
 	I915_WRITE(CNL_PORT_TX_DW7_GRP(port), val);
 }