[PATCH v14 07/10] drm/mediatek: add hpd debounce

Bo-Chen Chen
2022-07-12T11:13:09Z

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>
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 | 23 +++++++++++++++++++++++
1 file changed, 23 insertions(+)

diff --git a/drivers/gpu/drm/mediatek/mtk_dp.c b/drivers/gpu/drm/mediatek/mtk_dp.c
index 610651dd6365..50a4159095a1 100644
--- a/drivers/gpu/drm/mediatek/mtk_dp.c
+++ b/drivers/gpu/drm/mediatek/mtk_dp.c
@@ -105,6 +105,8 @@ struct mtk_dp {
bool enabled;

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

static struct regmap_config mtk_dp_regmap_config = {
@@ -1551,7 +1553,11 @@ 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_dbg(mtk_dp->dev, "drm_helper_hpd_irq_event\n");
+
drm_helper_hpd_irq_event(mtk_dp->bridge.dev);

if (mtk_dp->train_info.cable_state_change) {
@@ -1614,6 +1620,12 @@ 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;
}

@@ -2058,6 +2070,13 @@ 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;
@@ -2135,6 +2154,9 @@ 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);

@@ -2147,6 +2169,7 @@ 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