[Intel-gfx] [PATCH v2] drm/i915: Lock gmbus/aux mutexes while changing cdclk

[Ville Syrjala]

From: Ville Syrjälä <ville.syrjala at linux.intel.com>

gmbus/aux may be clocked by cdclk, thus we should make sure no
transfers are ongoing while the cdclk frequency is being changed.
We do that by simply grabbing all the gmbus/aux mutexes. No one
else should be holding any more than one of those at a time so
the lock ordering here shouldn't matter.

v2: Use mutex_lock_nest_lock() (Chris)

Cc: Chris Wilson <chris at chris-wilson.co.uk>
Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
---
 drivers/gpu/drm/i915/display/intel_cdclk.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_cdclk.c b/drivers/gpu/drm/i915/display/intel_cdclk.c
index 0741d643455b..979a0241fdcb 100644
--- a/drivers/gpu/drm/i915/display/intel_cdclk.c
+++ b/drivers/gpu/drm/i915/display/intel_cdclk.c
@@ -1868,6 +1868,8 @@ static void intel_set_cdclk(struct drm_i915_private *dev_priv,
 			    const struct intel_cdclk_config *cdclk_config,
 			    enum pipe pipe)
 {
+	struct intel_encoder *encoder;
+
 	if (!intel_cdclk_changed(&dev_priv->cdclk.hw, cdclk_config))
 		return;
 
@@ -1876,8 +1878,28 @@ static void intel_set_cdclk(struct drm_i915_private *dev_priv,
 
 	intel_dump_cdclk_config(cdclk_config, "Changing CDCLK to");
 
+	/*
+	 * Lock aux/gmbus while we change cdclk in case those
+	 * functions use cdclk. Not all platforms/ports do,
+	 * but we'll lock them all for simplicity.
+	 */
+	mutex_lock(&dev_priv->gmbus_mutex);
+	for_each_intel_dp(&dev_priv->drm, encoder) {
+		struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
+
+		mutex_lock_nest_lock(&intel_dp->aux.hw_mutex,
+				     &dev_priv->gmbus_mutex);
+	}
+
 	dev_priv->display.set_cdclk(dev_priv, cdclk_config, pipe);
 
+	for_each_intel_dp(&dev_priv->drm, encoder) {
+		struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
+
+		mutex_unlock(&intel_dp->aux.hw_mutex);
+	}
+	mutex_unlock(&dev_priv->gmbus_mutex);
+
 	if (drm_WARN(&dev_priv->drm,
 		     intel_cdclk_changed(&dev_priv->cdclk.hw, cdclk_config),
 		     "cdclk state doesn't match!\n")) {
-- 
2.24.1