linux-kernel - [PATCH] USB: serial: cp210x: work around silicon bug setting break

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Message-Id: <20230426234221.1867222-1-minyard@acm.org>
Date:   Wed, 26 Apr 2023 18:42:21 -0500
From:   minyard@....org
To:     Craig Shelley <craig@...rotron.org.uk>,
        Johan Hovold <johan@...nel.org>
Cc:     Linux Kernel <linux-kernel@...r.kernel.org>,
        linux-usb@...r.kernel.org, Corey Minyard <cmimyard@...sta.com>
Subject: [PATCH] USB: serial: cp210x: work around silicon bug setting break

From: Corey Minyard <cmimyard@...sta.com>

At least on the CP2105, sending this once doesn't work, you have to send
it twice to make it happen.  If you only send it once, you will get a
really short time (a few bits) where the break is sent, right when the
break is turned off, thus it isn't recognised as a break.  Sending it
twice won't hurt anything, so just do it all the time.

Signed-off-by: Corey Minyard <cmimyard@...sta.com>
---
I played with this a bit, and found this change fixes the issue.  It's
not ideal, I suppose, but it works.

 drivers/usb/serial/cp210x.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/usb/serial/cp210x.c b/drivers/usb/serial/cp210x.c
index cdea1bff3b70..e410a749325b 100644
--- a/drivers/usb/serial/cp210x.c
+++ b/drivers/usb/serial/cp210x.c
@@ -1446,6 +1446,15 @@ static void cp210x_break_ctl(struct tty_struct *tty, int break_state)
 	dev_dbg(&port->dev, "%s - turning break %s\n", __func__,
 		state == BREAK_OFF ? "off" : "on");
 	cp210x_write_u16_reg(port, CP210X_SET_BREAK, state);
+	/*
+	 * At least on the CP2105, sending this once doesn't work, you
+	 * have to send it twice to make it happen.  If you only send
+	 * it once, you will get a really short time (a few bits) where
+	 * the break is sent, right when the break is turned off, thus
+	 * it isn't recognised as a break.  Sending it twice won't hurt
+	 * anything, so just do it all the time.
+	 */
+	cp210x_write_u16_reg(port, CP210X_SET_BREAK, state);
 }
 
 #ifdef CONFIG_GPIOLIB
-- 
2.35.7