Re: [PATCH v17 09/10] drm/mediatek: dp: Add hpd debounce

[CK Hu]

Hi, Bo-Chen:

On Thu, 2022-09-01 at 12:41 +0800, Bo-Chen Chen wrote:
> From: Jitao Shi <jitao.shi@xxxxxxxxxxxx>
> 
> 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)

Reviewed-by: CK Hu <ck.hu@xxxxxxxxxxxx>

> 
> Tested-by: Rex-BC Chen <rex-bc.chen@xxxxxxxxxxxx>
> Reviewed-by: Rex-BC Chen <rex-bc.chen@xxxxxxxxxxxx>
> Signed-off-by: Jitao Shi <jitao.shi@xxxxxxxxxxxx>
> Signed-off-by: Guillaume Ranquet <granquet@xxxxxxxxxxxx>
> Signed-off-by: Bo-Chen Chen <rex-bc.chen@xxxxxxxxxxxx>
> Reviewed-by: AngeloGioacchino Del Regno <
> angelogioacchino.delregno@xxxxxxxxxxxxx>
> ---
>  drivers/gpu/drm/mediatek/mtk_dp.c | 25 ++++++++++++++++++++++++-
>  1 file changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_dp.c
> b/drivers/gpu/drm/mediatek/mtk_dp.c
> index 11a94927c0d0..dd34dae417e5 100644
> --- a/drivers/gpu/drm/mediatek/mtk_dp.c
> +++ b/drivers/gpu/drm/mediatek/mtk_dp.c
> @@ -87,6 +87,7 @@ struct mtk_dp_efuse_fmt {
>  
>  struct mtk_dp {
>  	bool enabled;
> +	bool need_debounce;
>  	u8 max_lanes;
>  	u8 max_linkrate;
>  	u8 rx_cap[DP_RECEIVER_CAP_SIZE];
> @@ -109,6 +110,7 @@ struct mtk_dp {
>  	struct platform_device *phy_dev;
>  	struct phy *phy;
>  	struct regmap *regs;
> +	struct timer_list debounce_timer;
>  };
>  
>  struct mtk_dp_data {
> @@ -1475,14 +1477,24 @@ static irqreturn_t
> mtk_dp_hpd_event_thread(int hpd, void *dev)
>  	unsigned long flags;
>  	u32 status;
>  
> +	if (mtk_dp->need_debounce && mtk_dp-
> >train_info.cable_plugged_in)
> +		msleep(100);
> +
>  	spin_lock_irqsave(&mtk_dp->irq_thread_lock, flags);
>  	status = mtk_dp->irq_thread_handle;
>  	mtk_dp->irq_thread_handle = 0;
>  	spin_unlock_irqrestore(&mtk_dp->irq_thread_lock, flags);
>  
> -	if (status & MTK_DP_THREAD_CABLE_STATE_CHG)
> +	if (status & MTK_DP_THREAD_CABLE_STATE_CHG) {
>  		drm_helper_hpd_irq_event(mtk_dp->bridge.dev);
>  
> +		if (!mtk_dp->train_info.cable_plugged_in) {
> +			mtk_dp->need_debounce = false;
> +			mod_timer(&mtk_dp->debounce_timer,
> +				  jiffies + msecs_to_jiffies(100) - 1);
> +		}
> +	}
> +
>  	if (status & MTK_DP_THREAD_HPD_EVENT)
>  		dev_dbg(mtk_dp->dev, "Receive IRQ from sink
> devices\n");
>  
> @@ -1996,6 +2008,13 @@ 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;
> @@ -2069,6 +2088,9 @@ static int mtk_dp_probe(struct platform_device
> *pdev)
>  
>  	drm_bridge_add(&mtk_dp->bridge);
>  
> +	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);
>  
> @@ -2081,6 +2103,7 @@ static int mtk_dp_remove(struct platform_device
> *pdev)
>  
>  	pm_runtime_put(&pdev->dev);
>  	pm_runtime_disable(&pdev->dev);
> +	del_timer_sync(&mtk_dp->debounce_timer);
>  	drm_bridge_remove(&mtk_dp->bridge);
>  	platform_device_unregister(mtk_dp->phy_dev);
>