drm/i915: Do not touch the PCH SSC reference if a PLL is using it

Our PCH refclk init code currently assumes that the PCH SSC reference
can only be used for FDI. That is not true and it can be used by
SPLL/WRPLL for eDP SSC or clock bending as well. Before we go
reconfiguring it let's make sure no PLL is currently using the PCH
SSC reference.

For some reason the hw is not particularly upset about losing
the clock if we immediately follow up with a modeset. Can't
really explain why nothing times out during the crtc disable
at least, but that's what the logs say. With fastboot the
story is quite different and we lose the entire display if
we turn off the PCH SSC reference when it's still being used.

Since we totally skip configuring the PCH SSC reference it
may not be in the proper state for FDI. Hopefully that won't
be a problem in practice.

We really should move this code to be part of the modeset seqeuence
and properly deal with the potentially conflicting requirements
imposed on PLL reference clocks. But that requires actual work.
Let's toss in a TODO for that.

v2: Pimp the commit message with the fastboot vs. not
    details

Cc: Julius B. <freedesktop@blln.gr>
Cc: Johannes Krampf <johannes.krampf@gmail.com>
Tested-by: Johannes Krampf <johannes.krampf@gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=108773Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190604200933.29417-1-ville.syrjala@linux.intel.comReviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>

drivers/gpu/drm/i915/i915_reg.h

@@ -7512,6 +7512,7 @@ enum {
 #define  ILK_eDP_A_DISABLE		(1 << 24)
 #define  HSW_CDCLK_LIMIT		(1 << 24)
 #define  ILK_DESKTOP			(1 << 23)
+#define  HSW_CPU_SSC_ENABLE		(1 << 21)
 
 #define ILK_DSPCLK_GATE_D			_MMIO(0x42020)
 #define   ILK_VRHUNIT_CLOCK_GATE_DISABLE	(1 << 28)

drivers/gpu/drm/i915/intel_display.c

@@ -9126,22 +9126,95 @@ static void lpt_bend_clkout_dp(struct drm_i915_private *dev_priv, int steps)
 
 #undef BEND_IDX
 
+static bool spll_uses_pch_ssc(struct drm_i915_private *dev_priv)
+{
+	u32 fuse_strap = I915_READ(FUSE_STRAP);
+	u32 ctl = I915_READ(SPLL_CTL);
+
+	if ((ctl & SPLL_PLL_ENABLE) == 0)
+		return false;
+
+	if ((ctl & SPLL_PLL_REF_MASK) == SPLL_PLL_SSC &&
+	    (fuse_strap & HSW_CPU_SSC_ENABLE) == 0)
+		return true;
+
+	if (IS_BROADWELL(dev_priv) &&
+	    (ctl & SPLL_PLL_REF_MASK) == SPLL_PLL_NON_SSC)
+		return true;
+
+	return false;
+}
+
+static bool wrpll_uses_pch_ssc(struct drm_i915_private *dev_priv,
+			       enum intel_dpll_id id)
+{
+	u32 fuse_strap = I915_READ(FUSE_STRAP);
+	u32 ctl = I915_READ(WRPLL_CTL(id));
+
+	if ((ctl & WRPLL_PLL_ENABLE) == 0)
+		return false;
+
+	if ((ctl & WRPLL_PLL_REF_MASK) == WRPLL_PLL_SSC)
+		return true;
+
+	if ((IS_BROADWELL(dev_priv) || IS_HSW_ULT(dev_priv)) &&
+	    (ctl & WRPLL_PLL_REF_MASK) == WRPLL_PLL_NON_SSC &&
+	    (fuse_strap & HSW_CPU_SSC_ENABLE) == 0)
+		return true;
+
+	return false;
+}
+
 static void lpt_init_pch_refclk(struct drm_i915_private *dev_priv)
 {
 	struct intel_encoder *encoder;
-	bool has_vga = false;
+	bool pch_ssc_in_use = false;
+	bool has_fdi = false;
 
 	for_each_intel_encoder(&dev_priv->drm, encoder) {
 		switch (encoder->type) {
 		case INTEL_OUTPUT_ANALOG:
-			has_vga = true;
+			has_fdi = true;
 			break;
 		default:
 			break;
 		}
 	}
 
-	if (has_vga) {
+	/*
+	 * The BIOS may have decided to use the PCH SSC
+	 * reference so we must not disable it until the
+	 * relevant PLLs have stopped relying on it. We'll
+	 * just leave the PCH SSC reference enabled in case
+	 * any active PLL is using it. It will get disabled
+	 * after runtime suspend if we don't have FDI.
+	 *
+	 * TODO: Move the whole reference clock handling
+	 * to the modeset sequence proper so that we can
+	 * actually enable/disable/reconfigure these things
+	 * safely. To do that we need to introduce a real
+	 * clock hierarchy. That would also allow us to do
+	 * clock bending finally.
+	 */
+	if (spll_uses_pch_ssc(dev_priv)) {
+		DRM_DEBUG_KMS("SPLL using PCH SSC\n");
+		pch_ssc_in_use = true;
+	}
+
+	if (wrpll_uses_pch_ssc(dev_priv, DPLL_ID_WRPLL1)) {
+		DRM_DEBUG_KMS("WRPLL1 using PCH SSC\n");
+		pch_ssc_in_use = true;
+	}
+
+	if (wrpll_uses_pch_ssc(dev_priv, DPLL_ID_WRPLL2)) {
+		DRM_DEBUG_KMS("WRPLL2 using PCH SSC\n");
+		pch_ssc_in_use = true;
+	}
+
+	if (pch_ssc_in_use)
+		return;
+
+	if (has_fdi) {
 		lpt_bend_clkout_dp(dev_priv, 0);
 		lpt_enable_clkout_dp(dev_priv, true, true);
 	} else {