drm: bridge/dw_hdmi: fix phy enable/disable handling

The dw_hdmi enable/disable handling is particularly weak in several
regards:
* The hotplug interrupt could call hdmi_poweron() or hdmi_poweroff()
  while DRM is setting a mode, which could race with a mode being set.
* Hotplug will always re-enable the phy whenever it detects an active
  hotplug signal, even if DRM has disabled the output.

Resolve all of these by introducing a mutex to prevent races, and a
state-tracking bool so we know whether DRM wishes the output to be
enabled.  We choose to use our own mutex rather than ->struct_mutex
so that we can still process interrupts in a timely fashion.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 22 insertions, 7 deletions

diff --git a/drivers/gpu/drm/bridge/dw_hdmi.c b/drivers/gpu/drm/bridge/dw_hdmi.c
index cef31d5cacb3..c5c4553258b6 100644
--- a/drivers/gpu/drm/bridge/dw_hdmi.c
+++ b/drivers/gpu/drm/bridge/dw_hdmi.c
@@ -125,6 +125,9 @@ struct dw_hdmi {
         bool sink_is_hdmi;
         bool sink_has_audio;
 
+        struct mutex mutex;             /* for state below and previous_mode */
+        bool disabled;                  /* DRM has disabled our bridge */
+
         spinlock_t audio_lock;
         struct mutex audio_mutex;
         unsigned int sample_rate;
@@ -1375,8 +1378,12 @@ static void dw_hdmi_bridge_mode_set(struct drm_bridge *bridge,
 {
         struct dw_hdmi *hdmi = bridge->driver_private;
 
+        mutex_lock(&hdmi->mutex);
+
         /* Store the display mode for plugin/DKMS poweron events */
         memcpy(&hdmi->previous_mode, mode, sizeof(hdmi->previous_mode));
+
+        mutex_unlock(&hdmi->mutex);
 }
 
 static bool dw_hdmi_bridge_mode_fixup(struct drm_bridge *bridge,
@@ -1390,14 +1397,20 @@ static void dw_hdmi_bridge_disable(struct drm_bridge *bridge)
 {
         struct dw_hdmi *hdmi = bridge->driver_private;
 
+        mutex_lock(&hdmi->mutex);
+        hdmi->disabled = true;
         dw_hdmi_poweroff(hdmi);
+        mutex_unlock(&hdmi->mutex);
 }
 
 static void dw_hdmi_bridge_enable(struct drm_bridge *bridge)
 {
         struct dw_hdmi *hdmi = bridge->driver_private;
 
+        mutex_lock(&hdmi->mutex);
         dw_hdmi_poweron(hdmi);
+        hdmi->disabled = false;
+        mutex_unlock(&hdmi->mutex);
 }
 
 static void dw_hdmi_bridge_nop(struct drm_bridge *bridge)
@@ -1520,20 +1533,20 @@ static irqreturn_t dw_hdmi_irq(int irq, void *dev_id)
         phy_int_pol = hdmi_readb(hdmi, HDMI_PHY_POL0);
 
         if (intr_stat & HDMI_IH_PHY_STAT0_HPD) {
+                hdmi_modb(hdmi, ~phy_int_pol, HDMI_PHY_HPD, HDMI_PHY_POL0);
+                mutex_lock(&hdmi->mutex);
                 if (phy_int_pol & HDMI_PHY_HPD) {
                         dev_dbg(hdmi->dev, "EVENT=plugin\n");
 
-                        hdmi_modb(hdmi, 0, HDMI_PHY_HPD, HDMI_PHY_POL0);
-
-                        dw_hdmi_poweron(hdmi);
+                        if (!hdmi->disabled)
+                                dw_hdmi_poweron(hdmi);
                 } else {
                         dev_dbg(hdmi->dev, "EVENT=plugout\n");
 
-                        hdmi_modb(hdmi, HDMI_PHY_HPD, HDMI_PHY_HPD,
-                                  HDMI_PHY_POL0);
-
-                        dw_hdmi_poweroff(hdmi);
+                        if (!hdmi->disabled)
+                                dw_hdmi_poweroff(hdmi);
                 }
+                mutex_unlock(&hdmi->mutex);
                 drm_helper_hpd_irq_event(hdmi->bridge->dev);
         }
 
@@ -1601,7 +1614,9 @@ int dw_hdmi_bind(struct device *dev, struct device *master,
         hdmi->sample_rate = 48000;
         hdmi->ratio = 100;
         hdmi->encoder = encoder;
+        hdmi->disabled = true;
 
+        mutex_init(&hdmi->mutex);
         mutex_init(&hdmi->audio_mutex);
         spin_lock_init(&hdmi->audio_lock);