Re: [PATCH v12 07/10] drm/mediatek: add hpd debounce
From: AngeloGioacchino Del Regno
Date: Mon Jun 27 2022 - 06:19:21 EST
Il 27/06/22 10:03, Bo-Chen Chen ha scritto:
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)
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>