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);
>