[PATCH 10/12] drm: bridge/dw_hdmi: fix phy enable/disable handling

On Wed, Oct 07, 2015 at 12:05:37PM +0800, Yakir Yang wrote:

On 08/09/2015 12:04 AM, Russell King wrote:

quoted

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 <redacted>
---
 drivers/gpu/drm/bridge/dw_hdmi.c | 29 ++++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/bridge/dw_hdmi.c b/drivers/gpu/drm/bridge/dw_hdmi.c
index 7b8a4e942a71..0ee188930d26 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;

@@ -1389,8 +1392,12 @@ 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,

@@ -1404,14 +1411,20 @@ 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)

@@ -1534,20 +1547,20 @@ 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);

Just like my reply on 08/12, I thought this could be removed, so
poweron/poweroff would only be called with bridge->enable/
bridge->disable, them maybe no need mutex here.

The bridge enable/disable methods do not get called on hotplug changes.

[    1.363011] dwhdmi-imx 120000.hdmi: Detected HDMI controller 0x13:0xa:0xa0:0xc1
[    1.371341] dwhdmi-imx 120000.hdmi: dw_hdmi_irq(I:RX----,HPD P:RX3210,HPD S:RX----,HPD)
[    1.381345] imx-drm display-subsystem: bound 120000.hdmi (ops dw_hdmi_imx_ops)
[    1.448691] dwhdmi-imx 120000.hdmi: dw_hdmi_bridge_disable()
[    1.450963] dwhdmi-imx 120000.hdmi: dw_hdmi_bridge_enable()

and then unplugging and re-plugging the HDMI cable:

[   68.307505] dwhdmi-imx 120000.hdmi: dw_hdmi_irq(I:RX----,HPD P:RX3210,--- S:RX----,---)
[   73.813970] dwhdmi-imx 120000.hdmi: dw_hdmi_irq(I:RX----,HPD P:RX3210,HPD S:RX----,HPD)

As you can see, during the period of disconnection for five seconds,
dw_hdmi_bridge_disable() was not called.

So, without the code above, we'd be needlessly wasting power with the
bridge enabled, trying to drive a disconnected display.

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