linux-kernel - [PATCH v11 07/10] drm/mediatek: add hpd debounce

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Date:   Fri, 10 Jun 2022 18:55:19 +0800
From:   Bo-Chen Chen <rex-bc.chen@...iatek.com>
To:     <chunkuang.hu@...nel.org>, <p.zabel@...gutronix.de>,
        <daniel@...ll.ch>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <mripard@...nel.org>,
        <tzimmermann@...e.de>, <matthias.bgg@...il.com>, <deller@....de>,
        <airlied@...ux.ie>
CC:     <msp@...libre.com>, <granquet@...libre.com>,
        <jitao.shi@...iatek.com>, <wenst@...omium.org>,
        <angelogioacchino.delregno@...labora.com>, <ck.hu@...iatek.com>,
        <dri-devel@...ts.freedesktop.org>,
        <linux-mediatek@...ts.infradead.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-fbdev@...r.kernel.org>,
        <Project_Global_Chrome_Upstream_Group@...iatek.com>,
        Bo-Chen Chen <rex-bc.chen@...iatek.com>
Subject: [PATCH v11 07/10] drm/mediatek: add hpd debounce

From: Jitao Shi <jitao.shi@...iatek.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@...iatek.com>
Reviewed-by: Rex-BC Chen <rex-bc.chen@...iatek.com>
Signed-off-by: Jitao Shi <jitao.shi@...iatek.com>
Signed-off-by: Guillaume Ranquet <granquet@...libre.com>
Signed-off-by: Bo-Chen Chen <rex-bc.chen@...iatek.com>
---
 drivers/gpu/drm/mediatek/mtk_dp.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/drivers/gpu/drm/mediatek/mtk_dp.c b/drivers/gpu/drm/mediatek/mtk_dp.c
index 7c2bb2a494dd..2413551bfe9f 100644
--- a/drivers/gpu/drm/mediatek/mtk_dp.c
+++ b/drivers/gpu/drm/mediatek/mtk_dp.c
@@ -129,6 +129,8 @@ 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 = {
@@ -1681,6 +1683,9 @@ 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);
+
 	dev_info(mtk_dp->dev, "drm_helper_hpd_irq_event\n");
 	drm_helper_hpd_irq_event(mtk_dp->bridge.dev);
 
@@ -1766,6 +1771,12 @@ 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;
 }
 
@@ -2216,6 +2227,13 @@ 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;
@@ -2295,6 +2313,9 @@ 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);
 
@@ -2307,6 +2328,7 @@ 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);
 
-- 
2.18.0