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

On Wed, Oct 07, 2015 at 06:40:11PM +0800, Yakir Yang wrote:

On 10/07/2015 05:48 PM, Russell King - ARM Linux wrote:

quoted

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

quoted

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.

Strangely, I do see bridge enable/disable in my side, past the log and
dump_stack bellow.

And I guess your HDMI maybe not really hot pluged, could you confirm that
the "status" of HDMI display card have been changed between "connected"
and "disconnected".

It does.

Do see bridge_disable when I unpluging the HDMI cable
[   16.358717] dwhdmi-rockchip ff980000.hdmi: EVENT=plugout
[   20.613221] [<c010e030>] (unwind_backtrace) from [<c010a4e0>]
(show_stack+0x20/0x24)
[   20.631561] [<c010a4e0>] (show_stack) from [<c0896828>]
(dump_stack+0x70/0x8c)
[   20.649337] [<c0896828>] (dump_stack) from [<c0414038>]
(dw_hdmi_bridge_disable+0x1c/0x88)
[   20.668178] [<c0414038>] (dw_hdmi_bridge_disable) from [<c03e3888>]
(drm_encoder_disable+0x34/0x78)
[   20.687857] [<c03e3888>] (drm_encoder_disable) from [<c03e3b1c>]
(__drm_helper_disable_unused_functions+0x68/0xe4)
[   20.708975] [<c03e3b1c>] (__drm_helper_disable_unused_functions) from
[<c03e4320>] (drm_crtc_helper_set_config+0x128/0x85c)
[   20.731180] [<c03e4320>] (drm_crtc_helper_set_config) from [<c03f5e3c>]
(drm_mode_set_config_internal+0x58/0xdc)
[   20.752507] [<c03f5e3c>] (drm_mode_set_config_internal) from [<c0405ed0>]
(commit_crtc_state+0x124/0x1ec)
[   20.773342] [<c0405ed0>] (commit_crtc_state) from [<c04055d4>]
(atomic_commit.isra.3+0x5c/0xc8)
[   20.793397] [<c04055d4>] (atomic_commit.isra.3) from [<c040565c>]
(drm_atomic_commit+0x1c/0x20)
[   20.813467] [<c040565c>] (drm_atomic_commit) from [<c03fa480>]
(drm_mode_setcrtc+0x324/0x3e4)
[   20.833379] [<c03fa480>] (drm_mode_setcrtc) from [<c03eb320>]
(drm_ioctl+0x304/0x478)
[   20.852557] [<c03eb320>] (drm_ioctl) from [<c021f024>]
(do_vfs_ioctl+0x494/0x5a8)
[   20.871377] [<c021f024>] (do_vfs_ioctl) from [<c021f194>]
(SyS_ioctl+0x5c/0x84)
[   20.890038] [<c021f194>] (SyS_ioctl) from [<c010646c>]
(__sys_trace_return+0x0/0x14)

Your userspace is issuing an ioctl to disable the output.  I guess you
have other active outputs besides HDMI.

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