drm/i915: Convert BUG_ON(!pll->active) and friends to a WARN

Turn a fatal lockup into a merely blank display with lots of shouty
messages.

v2: Whilst in the area, convert the other BUG_ON into less fatal errors.
In particular, note that we may be called on a PCH platform not using
PLLs, such as Haswell, and so we do not always want to BUG_ON(!pll)

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 15 insertions, 6 deletions

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 956b22899b7..9dc42bf557b 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -1403,14 +1403,18 @@ out_unlock:
 static void intel_enable_pch_pll(struct intel_crtc *intel_crtc)
 {
         struct drm_i915_private *dev_priv = intel_crtc->base.dev->dev_private;
-        struct intel_pch_pll *pll = intel_crtc->pch_pll;
+        struct intel_pch_pll *pll;
         int reg;
         u32 val;
 
-        /* PCH only available on ILK+ */
+        /* PCH PLLs only available on ILK, SNB and IVB */
         BUG_ON(dev_priv->info->gen < 5);
-        BUG_ON(pll == NULL);
-        BUG_ON(pll->refcount == 0);
+        pll = intel_crtc->pch_pll;
+        if (pll == NULL)
+                return;
+
+        if (WARN_ON(pll->refcount == 0))
+                return;
 
         DRM_DEBUG_KMS("enable PCH PLL %x (active %d, on? %d)for crtc %d\n",
                       pll->pll_reg, pll->active, pll->on,
@@ -1448,13 +1452,18 @@ static void intel_disable_pch_pll(struct intel_crtc *intel_crtc)
         if (pll == NULL)
                return;
 
-        BUG_ON(pll->refcount == 0);
+        if (WARN_ON(pll->refcount == 0))
+                return;
 
         DRM_DEBUG_KMS("disable PCH PLL %x (active %d, on? %d) for crtc %d\n",
                       pll->pll_reg, pll->active, pll->on,
                       intel_crtc->base.base.id);
 
-        BUG_ON(pll->active == 0);
+        if (WARN_ON(pll->active == 0)) {
+                assert_pch_pll_disabled(dev_priv, intel_crtc);
+                return;
+        }
+
         if (--pll->active) {
                 assert_pch_pll_enabled(dev_priv, intel_crtc);
                 return;