[PATCH] drm/i915: Don't try to use negative pll_id.

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

It is unlikely we are getting the -1 here.
But if we propagate that pll_id -1 to the rest of the code
we might have funny calculations on link_clock and who
knows what registers we end up accessing.

Better to protect the code.

Also better with errno number instead of generic -1.

Cc: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
---
 drivers/gpu/drm/i915/intel_ddi.c      | 10 ++++++++++
 drivers/gpu/drm/i915/intel_dpll_mgr.c |  2 +-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
index ace674cd79b9..2c6abdbf33ea 100644
--- a/drivers/gpu/drm/i915/intel_ddi.c
+++ b/drivers/gpu/drm/i915/intel_ddi.c
@@ -1283,6 +1283,11 @@ static void cnl_ddi_clock_get(struct intel_encoder *encoder,
 
 	pll_id = intel_get_shared_dpll_id(dev_priv, pipe_config->shared_dpll);
 
+	if (pll_id < 0) {
+		DRM_ERROR("PLL not found\n");
+		return;
+	}
+
 	cfgcr0 = I915_READ(CNL_DPLL_CFGCR0(pll_id));
 
 	if (cfgcr0 & DPLL_CFGCR0_HDMI_MODE) {
@@ -1337,6 +1342,11 @@ static void skl_ddi_clock_get(struct intel_encoder *encoder,
 
 	pll_id = intel_get_shared_dpll_id(dev_priv, pipe_config->shared_dpll);
 
+	if (pll_id < 0) {
+		DRM_ERROR("PLL not found\n");
+		return;
+	}
+
 	dpll_ctl1 = I915_READ(DPLL_CTRL1);
 
 	if (dpll_ctl1 & DPLL_CTRL1_HDMI_MODE(pll_id)) {
diff --git a/drivers/gpu/drm/i915/intel_dpll_mgr.c b/drivers/gpu/drm/i915/intel_dpll_mgr.c
index a83bf1c38e05..c4a7f39e173a 100644
--- a/drivers/gpu/drm/i915/intel_dpll_mgr.c
+++ b/drivers/gpu/drm/i915/intel_dpll_mgr.c
@@ -102,7 +102,7 @@ intel_get_shared_dpll_id(struct drm_i915_private *dev_priv,
 {
 	if (WARN_ON(pll < dev_priv->shared_dplls||
 		    pll > &dev_priv->shared_dplls[dev_priv->num_shared_dpll]))
-		return -1;
+		return -ENOENT;
 
 	return (enum intel_dpll_id) (pll - dev_priv->shared_dplls);
 }
-- 
2.13.6

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