linux-kernel - [PATCH 5.10 165/299] power: supply: cpcap-charger: Add usleep to cpcap charger to avoid usb plug bounce

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Message-Id: <20210510102010.401939099@linuxfoundation.org>
Date:   Mon, 10 May 2021 12:19:22 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Carl Philipp Klemm <philipp@...s.xyz>,
        Tony Lindgren <tony@...mide.com>,
        Sebastian Reichel <sebastian.reichel@...labora.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.10 165/299] power: supply: cpcap-charger: Add usleep to cpcap charger to avoid usb plug bounce

From: Carl Philipp Klemm <philipp@...s.xyz>

[ Upstream commit 751faedf06e895a17e985a88ef5b6364ffd797ed ]

Adds 80000 us sleep when the usb cable is plugged in to hopefully avoid
bouncing contacts.

Upon pluging in the usb cable vbus will bounce for some time, causing cpcap to
dissconnect charging due to detecting an undervoltage condition. This is a
scope of vbus on xt894 while quickly inserting the usb cable with firm force,
probed at the far side of the usb socket and vbus loaded with approx 1k:
http://uvos.xyz/maserati/usbplug.jpg.

As can clearly be seen, vbus is all over the place for the first 15 ms or so
with a small blip at ~40 ms this causes the cpcap to trip up and disable
charging again.

The delay helps cpcap_usb_detect avoid the worst of this. It is, however, still
not ideal as strong vibrations can cause the issue to reapear any time during
charging. I have however not been able to cause the device to stop charging due
to this in practice as it is hard to vibrate the device such that the vbus pins
start bouncing again but cpcap_usb_detect is not called again due to a detected
disconnect/reconnect event.

Signed-off-by: Carl Philipp Klemm <philipp@...s.xyz>
Tested-by: Tony Lindgren <tony@...mide.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@...labora.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/power/supply/cpcap-charger.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/power/supply/cpcap-charger.c b/drivers/power/supply/cpcap-charger.c
index 22fff01425d6..891e1eb8e39d 100644
--- a/drivers/power/supply/cpcap-charger.c
+++ b/drivers/power/supply/cpcap-charger.c
@@ -633,6 +633,9 @@ static void cpcap_usb_detect(struct work_struct *work)
 		return;
 	}

+	/* Delay for 80ms to avoid vbus bouncing when usb cable is plugged in */
+	usleep_range(80000, 120000);
+
 	/* Throttle chrgcurr2 interrupt for charger done and retry */
 	switch (ddata->state) {
 	case CPCAP_CHARGER_CHARGING:
-- 
2.30.2