drm/i915: Disable CLKOUT_DP bending on LPT/WPT as needed

When we want to use SPLL for FDI we want SSC, which means we have to
disable clock bending for the PCH SSC reference (bend and spread are
mutually exclusive). So let's turn off bending when we want spread.
In case the BIOS enabled clock bending for some reason we'll just turn
it off and enable the spread mode instead.

Not sure what happens if the BIOS is actually using the bend source for
HDMI at this time, but I suppose it should be no worse than what already
happens when we simply turn on the spread.

We don't currently use the bend source for anything, and only use the
PCH SSC reference for the SPLL to drive FDI (always with spread).

v2: Fix the %5 vs %10 fumble for SSCDITHPHASE (Paulo)
    Add 'WARN_ON(steps % 5 != 0)' sanity check (Paulo)
    Fix typos in commit message (Paulo)

Cc: Paulo Zanoni <[email protected]>
Signed-off-by: Ville Syrjälä <[email protected]>
Link: http://patchwork.freedesktop.org/patch/msgid/[email protected]
Reviewed-by: Paulo Zanoni <[email protected]>

Author: vsyrjala

drivers/gpu/drm/i915/i915_reg.h

@@ -7327,13 +7327,15 @@ enum skl_disp_power_wells {
 #define  SBI_READY			(0x0<<0)
 
 /* SBI offsets */
+#define  SBI_SSCDIVINTPHASE			0x0200
 #define  SBI_SSCDIVINTPHASE6			0x0600
 #define   SBI_SSCDIVINTPHASE_DIVSEL_MASK	((0x7f)<<1)
 #define   SBI_SSCDIVINTPHASE_DIVSEL(x)		((x)<<1)
 #define   SBI_SSCDIVINTPHASE_INCVAL_MASK	((0x7f)<<8)
 #define   SBI_SSCDIVINTPHASE_INCVAL(x)		((x)<<8)
 #define   SBI_SSCDIVINTPHASE_DIR(x)		((x)<<15)
 #define   SBI_SSCDIVINTPHASE_PROPAGATE		(1<<0)
+#define  SBI_SSCDITHPHASE			0x0204
 #define  SBI_SSCCTL				0x020c
 #define  SBI_SSCCTL6				0x060C
 #define   SBI_SSCCTL_PATHALT			(1<<3)

drivers/gpu/drm/i915/intel_display.c

@@ -8562,6 +8562,67 @@ static void lpt_disable_clkout_dp(struct drm_device *dev)
 	mutex_unlock(&dev_priv->sb_lock);
 }
 
+#define BEND_IDX(steps) ((50 + (steps)) / 5)
+
+static const uint16_t sscdivintphase[] = {
+	[BEND_IDX( 50)] = 0x3B23,
+	[BEND_IDX( 45)] = 0x3B23,
+	[BEND_IDX( 40)] = 0x3C23,
+	[BEND_IDX( 35)] = 0x3C23,
+	[BEND_IDX( 30)] = 0x3D23,
+	[BEND_IDX( 25)] = 0x3D23,
+	[BEND_IDX( 20)] = 0x3E23,
+	[BEND_IDX( 15)] = 0x3E23,
+	[BEND_IDX( 10)] = 0x3F23,
+	[BEND_IDX(  5)] = 0x3F23,
+	[BEND_IDX(  0)] = 0x0025,
+	[BEND_IDX( -5)] = 0x0025,
+	[BEND_IDX(-10)] = 0x0125,
+	[BEND_IDX(-15)] = 0x0125,
+	[BEND_IDX(-20)] = 0x0225,
+	[BEND_IDX(-25)] = 0x0225,
+	[BEND_IDX(-30)] = 0x0325,
+	[BEND_IDX(-35)] = 0x0325,
+	[BEND_IDX(-40)] = 0x0425,
+	[BEND_IDX(-45)] = 0x0425,
+	[BEND_IDX(-50)] = 0x0525,
+};
+
+/*
+ * Bend CLKOUT_DP
+ * steps -50 to 50 inclusive, in steps of 5
+ * < 0 slow down the clock, > 0 speed up the clock, 0 == no bend (135MHz)
+ * change in clock period = -(steps / 10) * 5.787 ps
+ */
+static void lpt_bend_clkout_dp(struct drm_i915_private *dev_priv, int steps)
+{
+	uint32_t tmp;
+	int idx = BEND_IDX(steps);
+
+	if (WARN_ON(steps % 5 != 0))
+		return;
+
+	if (WARN_ON(idx >= ARRAY_SIZE(sscdivintphase)))
+		return;
+
+	mutex_lock(&dev_priv->sb_lock);
+
+	if (steps % 10 != 0)
+		tmp = 0xAAAAAAAB;
+	else
+		tmp = 0x00000000;
+	intel_sbi_write(dev_priv, SBI_SSCDITHPHASE, tmp, SBI_ICLK);
+
+	tmp = intel_sbi_read(dev_priv, SBI_SSCDIVINTPHASE, SBI_ICLK);
+	tmp &= 0xffff0000;
+	tmp |= sscdivintphase[idx];
+	intel_sbi_write(dev_priv, SBI_SSCDIVINTPHASE, tmp, SBI_ICLK);
+
+	mutex_unlock(&dev_priv->sb_lock);
+}
+
+#undef BEND_IDX
+
 static void lpt_init_pch_refclk(struct drm_device *dev)
 {
 	struct intel_encoder *encoder;
@@ -8577,10 +8638,12 @@ static void lpt_init_pch_refclk(struct drm_device *dev)
 		}
 	}
 
-	if (has_vga)
+	if (has_vga) {
+		lpt_bend_clkout_dp(to_i915(dev), 0);
 		lpt_enable_clkout_dp(dev, true, true);
-	else
+	} else {
 		lpt_disable_clkout_dp(dev);
+	}
 }
 
 /*