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    SubjectRe: [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:
    > >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.

    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.

    --
    FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
    according to speedtest.net.


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