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    Subject[PATCH v10 20/21] drm/mediatek: add hpd debounce
    Date
    From: Jitao Shi <jitao.shi@mediatek.com>

    From the DP spec 1.4a chapter 3.3, upstream devices should implement
    HPD signal de-bouncing on an external connection.
    A period of 100ms should be used to detect an HPD connect event.
    To cover these cases, HPD de-bounce should be implemented only after
    HPD low has been detected for at least 100ms.

    Therefore,
    1. If HPD is low (which means plugging out) for longer than 100ms:
    we need to do de-bouncing (which means we need to wait for 100ms).
    2. If HPD low is for less than 100ms:
    we don't need to care about the de-bouncing.

    In this patch, we start a 100ms timer and use a need_debounce boolean
    to implement the feature.

    Two cases when HPD is high:
    1. If the timer is expired (>100ms):
    - need_debounce is true.
    - When HPD high (plugging event comes), need_debounce will be true
    and then we need to do de-bouncing (wait for 100ms).
    2. If the timer is not expired (<100ms):
    - need_debounce is false.
    - When HPD high (plugging event comes), need_debounce will be false
    and no need to do de-bouncing.

    HPD_______ __________________
    | |<- 100ms ->
    |____________|
    <- 100ms ->

    Without HPD de-bouncing, USB-C to HDMI Adapaters will not be detected.

    The change has been successfully tested with the following devices:
    - Dell Adapter - USB-C to HDMI
    - Acer 1in1 HDMI dongle
    - Ugreen 1in1 HDMI dongle
    - innowatt HDMI + USB3 hub
    - Acer 2in1 HDMI dongle
    - Apple 3in1 HDMI dongle (A2119)
    - J5Create 3in1 HDMI dongle (JAC379)

    Tested-by: Rex-BC Chen <rex-bc.chen@mediatek.com>
    Reviewed-by: Rex-BC Chen <rex-bc.chen@mediatek.com>
    Signed-off-by: Jitao Shi <jitao.shi@mediatek.com>
    Signed-off-by: Guillaume Ranquet <granquet@baylibre.com>
    ---
    drivers/gpu/drm/mediatek/mtk_dp.c | 21 +++++++++++++++++++++
    1 file changed, 21 insertions(+)

    diff --git a/drivers/gpu/drm/mediatek/mtk_dp.c b/drivers/gpu/drm/mediatek/mtk_dp.c
    index 4789853ec5ff..c056bc3ca9f6 100644
    --- a/drivers/gpu/drm/mediatek/mtk_dp.c
    +++ b/drivers/gpu/drm/mediatek/mtk_dp.c
    @@ -154,6 +154,8 @@ struct mtk_dp {
    struct mutex dp_lock;

    struct drm_connector *conn;
    + bool need_debounce;
    + struct timer_list debounce_timer;
    };

    static struct regmap_config mtk_dp_regmap_config = {
    @@ -1970,6 +1972,9 @@ static irqreturn_t mtk_dp_hpd_event_thread(int hpd, void *dev)
    if (event < 0)
    return IRQ_HANDLED;

    + if (mtk_dp->need_debounce && mtk_dp->train_info.cable_plugged_in)
    + msleep(100);
    +
    if (mtk_dp->drm_dev) {
    dev_info(mtk_dp->dev, "drm_helper_hpd_irq_event\n");
    drm_helper_hpd_irq_event(mtk_dp->bridge.dev);
    @@ -2047,6 +2052,11 @@ static irqreturn_t mtk_dp_hpd_isr_handler(struct mtk_dp *mtk_dp)
    }
    train_info->cable_state_change = true;

    + if (!train_info->cable_plugged_in) {
    + mod_timer(&mtk_dp->debounce_timer, jiffies + msecs_to_jiffies(100) - 1);
    + mtk_dp->need_debounce = false;
    + }
    +
    return IRQ_WAKE_THREAD;
    }

    @@ -2474,6 +2484,13 @@ static const struct drm_bridge_funcs mtk_dp_bridge_funcs = {
    .detect = mtk_dp_bdg_detect,
    };

    +static void mtk_dp_debounce_timer(struct timer_list *t)
    +{
    + struct mtk_dp *mtk_dp = from_timer(mtk_dp, t, debounce_timer);
    +
    + mtk_dp->need_debounce = true;
    +}
    +
    static int mtk_dp_probe(struct platform_device *pdev)
    {
    struct mtk_dp *mtk_dp;
    @@ -2547,6 +2564,9 @@ static int mtk_dp_probe(struct platform_device *pdev)
    else
    mtk_dp->bridge.type = DRM_MODE_CONNECTOR_DisplayPort;

    + mtk_dp->need_debounce = true;
    + timer_setup(&mtk_dp->debounce_timer, mtk_dp_debounce_timer, 0);
    +
    pm_runtime_enable(dev);
    pm_runtime_get_sync(dev);

    @@ -2559,6 +2579,7 @@ static int mtk_dp_remove(struct platform_device *pdev)

    platform_device_unregister(mtk_dp->phy_dev);
    mtk_dp_video_mute(mtk_dp, true);
    + del_timer_sync(&mtk_dp->debounce_timer);

    pm_runtime_disable(&pdev->dev);

    --
    2.35.1
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