drm/i915: Fix bounds check in intel_get_shared_dpll_id()

Fix an off-by-one error in the upper-bound check and while at it clear
up a bit the function.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200226203455.23032-2-imre.deak@intel.com

diff --git a/drivers/gpu/drm/i915/display/intel_dpll_mgr.c b/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
index e5bfe52..6cf2917 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
+++ b/drivers/gpu/drm/i915/display/intel_dpll_mgr.c
@@ -103,11 +103,14 @@ enum intel_dpll_id
 intel_get_shared_dpll_id(struct drm_i915_private *dev_priv,
                         struct intel_shared_dpll *pll)
 {
-       if (drm_WARN_ON(&dev_priv->drm, pll < dev_priv->shared_dplls ||
-                       pll > &dev_priv->shared_dplls[dev_priv->num_shared_dpll]))
+       long pll_idx = pll - dev_priv->shared_dplls;
+
+       if (drm_WARN_ON(&dev_priv->drm,
+                       pll_idx < 0 ||
+                       pll_idx >= dev_priv->num_shared_dpll))
                return -1;
 
-       return (enum intel_dpll_id) (pll - dev_priv->shared_dplls);
+       return pll_idx;
 }
 
 /* For ILK+ */