drm/i915: program iCLKIP on Lynx Point

The iCLKIP clock is used to drive the VGA pixel clock on the PCH. In order
to do so, it must be programmed to properly do the clock ticks according
to the divisor, phase direction, phase increments and a special auxiliary
divisor for 20MHz clock.

v2: calculate divisor values directly instead of relying on a table.

v3: merged a fix from Ben to properly check for invalid divider values.

Reviewed-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -2675,6 +2675,97 @@ static bool intel_crtc_driving_pch(struct drm_crtc *crtc)
 	return true;
 }
 
+/* Program iCLKIP clock to the desired frequency */
+static void lpt_program_iclkip(struct drm_crtc *crtc)
+{
+	struct drm_device *dev = crtc->dev;
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	u32 divsel, phaseinc, auxdiv, phasedir = 0;
+	u32 temp;
+
+	/* It is necessary to ungate the pixclk gate prior to programming
+	 * the divisors, and gate it back when it is done.
+	 */
+	I915_WRITE(PIXCLK_GATE, PIXCLK_GATE_GATE);
+
+	/* Disable SSCCTL */
+	intel_sbi_write(dev_priv, SBI_SSCCTL6,
+				intel_sbi_read(dev_priv, SBI_SSCCTL6) |
+					SBI_SSCCTL_DISABLE);
+
+	/* 20MHz is a corner case which is out of range for the 7-bit divisor */
+	if (crtc->mode.clock == 20000) {
+		auxdiv = 1;
+		divsel = 0x41;
+		phaseinc = 0x20;
+	} else {
+		/* The iCLK virtual clock root frequency is in MHz,
+		 * but the crtc->mode.clock in in KHz. To get the divisors,
+		 * it is necessary to divide one by another, so we
+		 * convert the virtual clock precision to KHz here for higher
+		 * precision.
+		 */
+		u32 iclk_virtual_root_freq = 172800 * 1000;
+		u32 iclk_pi_range = 64;
+		u32 desired_divisor, msb_divisor_value, pi_value;
+
+		desired_divisor = (iclk_virtual_root_freq / crtc->mode.clock);
+		msb_divisor_value = desired_divisor / iclk_pi_range;
+		pi_value = desired_divisor % iclk_pi_range;
+
+		auxdiv = 0;
+		divsel = msb_divisor_value - 2;
+		phaseinc = pi_value;
+	}
+
+	/* This should not happen with any sane values */
+	WARN_ON(SBI_SSCDIVINTPHASE_DIVSEL(divsel) &
+		~SBI_SSCDIVINTPHASE_DIVSEL_MASK);
+	WARN_ON(SBI_SSCDIVINTPHASE_DIR(phasedir) &
+		~SBI_SSCDIVINTPHASE_INCVAL_MASK);
+
+	DRM_DEBUG_KMS("iCLKIP clock: found settings for %dKHz refresh rate: auxdiv=%x, divsel=%x, phasedir=%x, phaseinc=%x\n",
+			crtc->mode.clock,
+			auxdiv,
+			divsel,
+			phasedir,
+			phaseinc);
+
+	/* Program SSCDIVINTPHASE6 */
+	temp = intel_sbi_read(dev_priv, SBI_SSCDIVINTPHASE6);
+	temp &= ~SBI_SSCDIVINTPHASE_DIVSEL_MASK;
+	temp |= SBI_SSCDIVINTPHASE_DIVSEL(divsel);
+	temp &= ~SBI_SSCDIVINTPHASE_INCVAL_MASK;
+	temp |= SBI_SSCDIVINTPHASE_INCVAL(phaseinc);
+	temp |= SBI_SSCDIVINTPHASE_DIR(phasedir);
+	temp |= SBI_SSCDIVINTPHASE_PROPAGATE;
+
+	intel_sbi_write(dev_priv,
+			SBI_SSCDIVINTPHASE6,
+			temp);
+
+	/* Program SSCAUXDIV */
+	temp = intel_sbi_read(dev_priv, SBI_SSCAUXDIV6);
+	temp &= ~SBI_SSCAUXDIV_FINALDIV2SEL(1);
+	temp |= SBI_SSCAUXDIV_FINALDIV2SEL(auxdiv);
+	intel_sbi_write(dev_priv,
+			SBI_SSCAUXDIV6,
+			temp);
+
+
+	/* Enable modulator and associated divider */
+	temp = intel_sbi_read(dev_priv, SBI_SSCCTL6);
+	temp &= ~SBI_SSCCTL_DISABLE;
+	intel_sbi_write(dev_priv,
+			SBI_SSCCTL6,
+			temp);
+
+	/* Wait for initialization time */
+	udelay(24);
+
+	I915_WRITE(PIXCLK_GATE, PIXCLK_GATE_UNGATE);
+}
+
 /*
  * Enable PCH resources required for PCH ports:
  *   - PCH PLLs
@@ -2694,11 +2785,14 @@ static void ironlake_pch_enable(struct drm_crtc *crtc)
 	/* For PCH output, training FDI link */
 	dev_priv->display.fdi_link_train(crtc);
 
-	intel_enable_pch_pll(intel_crtc);
-
-	if (HAS_PCH_CPT(dev)) {
+	if (HAS_PCH_LPT(dev)) {
+		DRM_DEBUG_KMS("LPT detected: programming iCLKIP\n");
+		lpt_program_iclkip(crtc);
+	} else if (HAS_PCH_CPT(dev)) {
 		u32 sel;
 
+		intel_enable_pch_pll(intel_crtc);
+
 		temp = I915_READ(PCH_DPLL_SEL);
 		switch (pipe) {
 		default: