linux-kernel - Re: [PATCH] drm/mediatek: DP HPD Detect with debounce

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Date:   Wed, 26 Jan 2022 00:44:14 +0800
From:   Chun-Kuang Hu <chunkuang.hu@...nel.org>
To:     Jitao Shi <jitao.shi@...iatek.com>
Cc:     Chun-Kuang Hu <chunkuang.hu@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        CK Hu <ck.hu@...iatek.com>, stonea168@....com,
        huijuan.xie@...iatek.com, Rex-BC Chen <rex-bc.chen@...iatek.com>,
        shuijing.li@...iatek.com, Rob Herring <robh+dt@...nel.org>,
        DTML <devicetree@...r.kernel.org>,
        Guillaume Ranquet <granquet@...libre.com>
Subject: Re: [PATCH] drm/mediatek: DP HPD Detect with debounce

Hi, Jitao:

Jitao Shi <jitao.shi@...iatek.com> 於 2022年1月12日 週三 下午11:01寫道：
>
> DP Spec 1.4a 3.3 requires dp detect the hpd with debounce.
>
> Upstream implementations should implement HPD signal de-bouncing on
> an external connection. A period of 100ms should be used for
> detecting an HPD connect event (i.e., the event, “HPD high,” is
> confirmed only after HPD has been continuously asserted for 100ms).
> Care should be taken to not implement de-bouncing on an IRQ_HPD and
> on a downstream device-generated pair of HPD disconnect/reconnect
> events (typically HPD shall be de-asserted for more than 2ms, but
> less than 100ms in this case). To cover these cases, HPD de-bounce
> should be implemented only after HPD low has been detected for 100ms.
>  Timing requirements in this Standard related to the detection of
> HPD high are to be interpreted as applying from the completion of an
> implementation-dependent de-bounce period.
>
> Signed-off-by: Jitao Shi <jitao.shi@...iatek.com>
> ---

mtk dp driver has not been upstreamed yet. This patch seems depend on
another series [1]. Please describe the dependency information here.

[1] https://patchwork.kernel.org/project/linux-mediatek/list/?series=597485

Regards,
Chun-Kuang.

>  drivers/gpu/drm/mediatek/mtk_dp.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
>
> diff --git a/drivers/gpu/drm/mediatek/mtk_dp.c b/drivers/gpu/drm/mediatek/mtk_dp.c
> index a256d55346a2..05f401a024a4 100644
> --- a/drivers/gpu/drm/mediatek/mtk_dp.c
> +++ b/drivers/gpu/drm/mediatek/mtk_dp.c
> @@ -193,6 +193,8 @@ struct mtk_dp {
>         struct mutex eld_lock;
>         u8 connector_eld[MAX_ELD_BYTES];
>         struct drm_connector *conn;
> +       bool need_debounce;
> +       struct timer_list debounce_timer;
>  };
>
>  enum mtk_dp_sdp_type {
> @@ -2217,6 +2219,9 @@ 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);
> @@ -2296,6 +2301,14 @@ static irqreturn_t mtk_dp_hpd_isr_handler(struct mtk_dp *mtk_dp)
>                 mtk_dp->train_state = MTK_DP_TRAIN_STATE_STARTUP;
>         }
>         train_info->cable_state_change = true;
> +
> +       if (train_info->cable_state_change) {
> +               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;
>  }
>
> @@ -2903,6 +2916,13 @@ static int mtk_dp_register_audio_driver(struct device *dev)
>         return 0;
>  }
>
> +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;
> @@ -2990,6 +3010,9 @@ 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);
> +
>         mtk_dp->bridge.ops =
>                 DRM_BRIDGE_OP_DETECT | DRM_BRIDGE_OP_EDID | DRM_BRIDGE_OP_HPD;
>         drm_bridge_add(&mtk_dp->bridge);
> @@ -3008,6 +3031,7 @@ static int mtk_dp_remove(struct platform_device *pdev)
>
>         mtk_dp_video_mute(mtk_dp, true);
>         mtk_dp_audio_mute(mtk_dp, true);
> +       del_timer_sync(&mtk_dp->debounce_timer);
>
>         pm_runtime_disable(&pdev->dev);
>
> --
> 2.12.5
>