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

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

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

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.

Best regards, - Yakir

}

• mutex_unlock(&hdmi->mutex);
  

  drm_helper_hpd_irq_event(hdmi->bridge->dev); }

@@ -1617,7 +1630,9 @@ 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);