drm/i915: reuse WRPLL when possible

It seems we do have machines with 3 HDMI/DVI outputs, so sharing
WRPLLs is the only way to get 3 pipes working.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=68485
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_ddi.c

@@ -713,8 +713,6 @@ bool intel_ddi_pll_mode_set(struct drm_crtc *crtc)
 	uint32_t reg, val;
 	int clock = intel_crtc->config.port_clock;
 
-	/* TODO: reuse PLLs when possible (compare values) */
-
 	intel_ddi_put_crtc_pll(crtc);
 
 	if (type == INTEL_OUTPUT_DISPLAYPORT || type == INTEL_OUTPUT_EDP) {
@@ -742,31 +740,40 @@ bool intel_ddi_pll_mode_set(struct drm_crtc *crtc)
 	} else if (type == INTEL_OUTPUT_HDMI) {
 		unsigned p, n2, r2;
 
-		if (plls->wrpll1_refcount == 0) {
+		intel_ddi_calculate_wrpll(clock * 1000, &r2, &n2, &p);
+
+		val = WRPLL_PLL_ENABLE | WRPLL_PLL_SELECT_LCPLL_2700 |
+		      WRPLL_DIVIDER_REFERENCE(r2) | WRPLL_DIVIDER_FEEDBACK(n2) |
+		      WRPLL_DIVIDER_POST(p);
+
+		if (val == I915_READ(WRPLL_CTL1)) {
+			DRM_DEBUG_KMS("Reusing WRPLL 1 on pipe %c\n",
+				      pipe_name(pipe));
+			reg = WRPLL_CTL1;
+		} else if (val == I915_READ(WRPLL_CTL2)) {
+			DRM_DEBUG_KMS("Reusing WRPLL 2 on pipe %c\n",
+				      pipe_name(pipe));
+			reg = WRPLL_CTL2;
+		} else if (plls->wrpll1_refcount == 0) {
 			DRM_DEBUG_KMS("Using WRPLL 1 on pipe %c\n",
 				      pipe_name(pipe));
-			plls->wrpll1_refcount++;
 			reg = WRPLL_CTL1;
-			intel_crtc->ddi_pll_sel = PORT_CLK_SEL_WRPLL1;
 		} else if (plls->wrpll2_refcount == 0) {
 			DRM_DEBUG_KMS("Using WRPLL 2 on pipe %c\n",
 				      pipe_name(pipe));
-			plls->wrpll2_refcount++;
 			reg = WRPLL_CTL2;
-			intel_crtc->ddi_pll_sel = PORT_CLK_SEL_WRPLL2;
 		} else {
 			DRM_ERROR("No WRPLLs available!\n");
 			return false;
 		}
 
-		WARN(I915_READ(reg) & WRPLL_PLL_ENABLE,
-		     "WRPLL already enabled\n");
-
-		intel_ddi_calculate_wrpll(clock * 1000, &r2, &n2, &p);
-
-		val = WRPLL_PLL_ENABLE | WRPLL_PLL_SELECT_LCPLL_2700 |
-		      WRPLL_DIVIDER_REFERENCE(r2) | WRPLL_DIVIDER_FEEDBACK(n2) |
-		      WRPLL_DIVIDER_POST(p);
+		if (reg == WRPLL_CTL1) {
+			plls->wrpll1_refcount++;
+			intel_crtc->ddi_pll_sel = PORT_CLK_SEL_WRPLL1;
+		} else {
+			plls->wrpll2_refcount++;
+			intel_crtc->ddi_pll_sel = PORT_CLK_SEL_WRPLL2;
+		}
 
 	} else if (type == INTEL_OUTPUT_ANALOG) {
 		if (plls->spll_refcount == 0) {