linux-kernel - [PATCH 2/4] USB: serial: io_ti: document reason for drain delay

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Message-Id: <20210412093815.736-3-johan@kernel.org>
Date:   Mon, 12 Apr 2021 11:38:13 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 2/4] USB: serial: io_ti: document reason for drain delay

Document that the device line-status register doesn't tell when the
transmitter shift register has emptied and that this is why the
one-character drain delay is needed.

Signed-off-by: Johan Hovold <johan@...nel.org>
---
 drivers/usb/serial/io_ti.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/usb/serial/io_ti.c b/drivers/usb/serial/io_ti.c
index 75325c2b295e..17720670e06c 100644
--- a/drivers/usb/serial/io_ti.c
+++ b/drivers/usb/serial/io_ti.c
@@ -2590,6 +2590,10 @@ static int edge_port_probe(struct usb_serial_port *port)
 	if (ret)
 		goto err;
 
+	/*
+	 * The LSR does not tell when the transmitter shift register has
+	 * emptied so add a one-character drain delay.
+	 */
 	port->port.drain_delay = 1;
 
 	return 0;
-- 
2.26.3