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 <przanoni@gmail.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1449260379-14093-1-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>

1 files changed, 65 insertions, 2 deletions

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index c6854de94b1f..c69a0d6c5a1e 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/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);
+	}
 }
 
 /*