drm/i915: Improve WRPLL reference clock readout on HSW/BDW

On non-ULT HSW the "special" WRPLL reference clock select
actually means non-SSC. Take that into account when reading
out the WRPLL state.

Also the non-SSC reference may be either 24MHz or 135MHz,
which we can read out from FUSE_STRAP3. The BDW docs actually
say: "also indicates whether the CPU and PCH are in a single
package or separate packages", so it may be that this is not
actually required and we could just assume 135 MHz (just like
the code already did). But it doesn't really hurt to read this
out as the HSW docs aren't quite so clear.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190604200933.29417-5-ville.syrjala@linux.intel.comReviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>

drivers/gpu/drm/i915/i915_reg.h

@@ -7514,6 +7514,9 @@ enum {
 #define  ILK_DESKTOP			(1 << 23)
 #define  HSW_CPU_SSC_ENABLE		(1 << 21)
 
+#define FUSE_STRAP3			_MMIO(0x42020)
+#define  HSW_REF_CLK_SELECT		(1 << 1)
+
 #define ILK_DSPCLK_GATE_D			_MMIO(0x42020)
 #define   ILK_VRHUNIT_CLOCK_GATE_DISABLE	(1 << 28)
 #define   ILK_DPFCUNIT_CLOCK_GATE_DISABLE	(1 << 9)

drivers/gpu/drm/i915/intel_ddi.c

@@ -1231,6 +1231,19 @@ static int hsw_ddi_calc_wrpll_link(struct drm_i915_private *dev_priv,
 	wrpll = I915_READ(reg);
 	switch (wrpll & WRPLL_REF_MASK) {
 	case WRPLL_REF_SPECIAL_HSW:
+		/*
+		 * muxed-SSC for BDW.
+		 * non-SSC for non-ULT HSW. Check FUSE_STRAP3
+		 * for the non-SSC reference frequency.
+		 */
+		if (IS_HASWELL(dev_priv) && !IS_HSW_ULT(dev_priv)) {
+			if (I915_READ(FUSE_STRAP3) & HSW_REF_CLK_SELECT)
+				refclk = 24;
+			else
+				refclk = 135;
+			break;
+		}
+		/* fall through */
 	case WRPLL_REF_PCH_SSC:
 		/*
 		 * We could calculate spread here, but our checking
@@ -1243,7 +1256,7 @@ static int hsw_ddi_calc_wrpll_link(struct drm_i915_private *dev_priv,
 		refclk = 2700;
 		break;
 	default:
-		WARN(1, "bad wrpll refclk\n");
+		MISSING_CASE(wrpll);
 		return 0;
 	}