linux-kernel - Re: [PATCH v2] serial: uart: add hw flow control support configuration

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Date:	Thu, 7 Aug 2014 10:12:54 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Murali Karicheri <m-karicheri2@...com>
Cc:	Peter Hurley <peter@...leysoftware.com>,
	devicetree@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	Jiri Slaby <jslaby@...e.cz>,
	Santosh Shilimkar <santosh.shilimkar@...com>
Subject: Re: [PATCH v2] serial: uart: add hw flow control support
 configuration

On Thu, Aug 07, 2014 at 12:16:59PM -0400, Murali Karicheri wrote:
> On 08/07/2014 11:29 AM, Peter Hurley wrote:
> >On 05/01/2014 03:04 PM, Murali Karicheri wrote:
> >>8250 uart driver currently supports only software assisted hw flow
> >>control. The software assisted hw flow control maintains a hw_stopped
> >>flag in the tty structure to stop and start transmission and use modem
> >>status interrupt for the event to drive the handshake signals. This is
> >>not needed if hw has flow control capabilities. This patch adds a
> >>DT attribute for enabling hw flow control for a uart port. Also skip
> >>stop and start if this flag is present in flag field of the port
> >>structure.
> >>
> >>Signed-off-by: Murali Karicheri<m-karicheri2@...com>
> >>
> >>CC: Rob Herring<robh+dt@...nel.org>
> >>CC: Pawel Moll<pawel.moll@....com>
> >>CC: Mark Rutland<mark.rutland@....com>
> >>CC: Ian Campbell<ijc+devicetree@...lion.org.uk>
> >>CC: Kumar Gala<galak@...eaurora.org>
> >>CC: Randy Dunlap<rdunlap@...radead.org>
> >>CC: Greg Kroah-Hartman<gregkh@...uxfoundation.org>
> >>CC: Jiri Slaby<jslaby@...e.cz>
> >>CC: Santosh Shilimkar<santosh.shilimkar@...com>
> >>---
> >>  .../devicetree/bindings/serial/of-serial.txt       |    1 +
> >>  drivers/tty/serial/8250/8250_core.c                |    6 ++++--
> >>  drivers/tty/serial/of_serial.c                     |    4 ++++
> >>  drivers/tty/serial/serial_core.c                   |   12 +++++++++---
> >>  4 files changed, 18 insertions(+), 5 deletions(-)
> >>
> >[...]
> >
> >>diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> >>index b68550d..851707a 100644
> >>--- a/drivers/tty/serial/serial_core.c
> >>+++ b/drivers/tty/serial/serial_core.c
> >>@@ -174,8 +174,12 @@ static int uart_port_startup(struct tty_struct *tty, struct uart_state *state,
> >>  			if (tty->termios.c_cflag&  CBAUD)
> >>  				uart_set_mctrl(uport, TIOCM_RTS | TIOCM_DTR);
> >>  		}
> >>-
> >>-		if (tty_port_cts_enabled(port)) {
> >>+		/*
> >>+		 * if hw support flow control without software intervention,
> >>+		 * then skip the below check
> >>+		 */
> >>+		if (tty_port_cts_enabled(port)&&
> >>+		    !(uport->flags&  UPF_HARD_FLOW)) {
> >>  			spin_lock_irq(&uport->lock);
> >>  			if (!(uport->ops->get_mctrl(uport)&  TIOCM_CTS))
> >>  				tty->hw_stopped = 1;
> >>@@ -2772,7 +2776,9 @@ void uart_handle_cts_change(struct uart_port *uport, unsigned int status)
> >>
> >>  	uport->icount.cts++;
> >>
> >>-	if (tty_port_cts_enabled(port)) {
> >>+	/* skip below code if the hw flow control is supported */
> >>+	if (tty_port_cts_enabled(port)&&
> >>+	    !(uport->flags&  UPF_HARD_FLOW)) {
> >Why is a modem status interrupt being generated for DCTS
> >if autoflow control is enabled?
> >
> >This should be:
> >
> >	WARN_ON_ONCE(uport->flags&  UPF_HARD_FLOW);
> >
> >to indicate a mis-configured driver/device.
> This patch is already merged to the upstream branch and if you see any
> issue, please
> post a patch for review.

If someone points out a problem in a patch of yours that is accepted
upstream, it is nice to provide a fix, otherwise I will just revert it
upstream, as it looks to be incorrect.

So, should I just revert it?

greg k-h
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