On Fri, Sep 20, 2019 at 02:49:51PM -0500, John Goerzen wrote: > Hello, > > I have narrowed down the issue I'm about to describe to keyspan.c; a > Digi Edgeport/1 with identical configuration works fine. > > I am configuring a Raspberry Pi running 4.19.66 (though keyspan.c hasn't > changed since 2017) to talk to a real-live vt420. Configuring agetty > with systemd worked easy enough, but I found that XON/XOFF wasn't > working. stty -a shows ixon and ixoff as appropriate, but sending > Ctrl-S (tested from multiple ways of sending) had no effect on output in > bash, or scrolling output. (Emacs, though, recognized it as the start > of a search, so I knew it was getting down the line.) > > > After a great deal of head-scratching on this, I went to look at the > kernel source and found that keyspan.c does not appear to be honoring > XOFF. I also have a Digi Edgeport/1 on hand (which uses io_ti.c), and > when I swapped to that, everything worked fine - Ctrl-S caused the > expected pause. > > As far as I can tell, keyspan.c simply never implemented handling of > XOFF, but you guys are the experts there. That's correct, the driver does not support software flow control even if the hardware seems to have some support for assisted XON/XOFF. Would you mind testing the below patch which may be enough to turn sw-flow control always on. If that works, I can probably find time to cook up a proper patch to make this configurable later this week. Johan >From 55b46d78fe63f182923e4674659fa18f4624d6b8 Mon Sep 17 00:00:00 2001 From: Johan Hovold <johan@xxxxxxxxxx> Date: Mon, 23 Sep 2019 12:14:56 +0200 Subject: [PATCH] USB: serial: keyspan: enable XON flow control Signed-off-by: Johan Hovold <johan@xxxxxxxxxx> --- drivers/usb/serial/keyspan.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/drivers/usb/serial/keyspan.c b/drivers/usb/serial/keyspan.c index d34779fe4a8d..934430cbdfc4 100644 --- a/drivers/usb/serial/keyspan.c +++ b/drivers/usb/serial/keyspan.c @@ -2118,7 +2118,7 @@ static int keyspan_usa26_send_setup(struct usb_serial *serial, msg.setLcr = 0xff; msg.ctsFlowControl = (p_priv->flow_control == flow_cts); - msg.xonFlowControl = 0; + msg.xonFlowControl = 1; msg.setFlowControl = 0xff; msg.forwardingLength = 16; msg.xonChar = 17; @@ -2234,7 +2234,7 @@ static int keyspan_usa28_send_setup(struct usb_serial *serial, msg.parity = 0; /* XXX for now */ msg.ctsFlowControl = (p_priv->flow_control == flow_cts); - msg.xonFlowControl = 0; + msg.xonFlowControl = 1; /* Do handshaking outputs, DTR is inverted relative to RTS */ msg.rts = p_priv->rts_state; @@ -2388,7 +2388,7 @@ static int keyspan_usa49_send_setup(struct usb_serial *serial, msg.setLcr = 0xff; msg.ctsFlowControl = (p_priv->flow_control == flow_cts); - msg.xonFlowControl = 0; + msg.xonFlowControl = 1; msg.setFlowControl = 0xff; msg.forwardingLength = 16; @@ -2690,7 +2690,7 @@ static int keyspan_usa67_send_setup(struct usb_serial *serial, msg.setLcr = 0xff; msg.ctsFlowControl = (p_priv->flow_control == flow_cts); - msg.xonFlowControl = 0; + msg.xonFlowControl = 1; msg.setFlowControl = 0xff; msg.forwardingLength = 16; msg.xonChar = 17; -- 2.23.0
