From 696c541c8c6cfa05d65aa24ae2b9e720fc01766e Mon Sep 17 00:00:00 2001
From: Johan Hovold <johan@kernel.org>
Date: Sun, 25 Oct 2020 18:45:47 +0100
Subject: [PATCH] USB: serial: keyspan_pda: fix dropped unthrottle interrupts
Git-commit: 696c541c8c6cfa05d65aa24ae2b9e720fc01766e
Patch-mainline: v5.11-rc1
References: git-fixes

Commit c528fcb116e6 ("USB: serial: keyspan_pda: fix receive sanity
checks") broke write-unthrottle handling by dropping well-formed
unthrottle-interrupt packets which are precisely two bytes long. This
could lead to blocked writers not being woken up when buffer space again
becomes available.

Instead, stop unconditionally printing the third byte which is
(presumably) only valid on modem-line changes.

Fixes: c528fcb116e6 ("USB: serial: keyspan_pda: fix receive sanity checks")
Cc: stable <stable@vger.kernel.org>     # 4.11
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/usb/serial/keyspan_pda.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/serial/keyspan_pda.c b/drivers/usb/serial/keyspan_pda.c
index c1333919716b..2d5ad579475a 100644
--- a/drivers/usb/serial/keyspan_pda.c
+++ b/drivers/usb/serial/keyspan_pda.c
@@ -172,11 +172,11 @@ static void keyspan_pda_rx_interrupt(struct urb *urb)
 		break;
 	case 1:
 		/* status interrupt */
-		if (len < 3) {
+		if (len < 2) {
 			dev_warn(&port->dev, "short interrupt message received\n");
 			break;
 		}
-		dev_dbg(&port->dev, "rx int, d1=%d, d2=%d\n", data[1], data[2]);
+		dev_dbg(&port->dev, "rx int, d1=%d\n", data[1]);
 		switch (data[1]) {
 		case 1: /* modemline change */
 			break;
-- 
2.26.2