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

CK Hu
2022-09-02T08:14:22Z

Hi, Bo-Chen:

On Thu, 2022-09-01 at 12:41 +0800, Bo-Chen Chen wrote:
> 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)

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

>
> 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>
> Signed-off-by: Bo-Chen Chen <rex-bc.chen@mediatek.com>
> Reviewed-by: AngeloGioacchino Del Regno <
> angelogioacchino.delregno@collabora.com>
> ---
> 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);
>