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Date: Wed, 28 May 2014 14:04:29 -0600
From: Dann Frazier <dann.frazier@...onical.com>
To: Murali Karicheri <m-karicheri2@...com>
Cc: 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>,
Greg Kroah-Hartman <gregkh@...uxfoundation.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, May 1, 2014 at 1:04 PM, Murali Karicheri <m-karicheri2@...com> 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.
ubuntu@...low:~$ sudo stty -a --file /dev/ttyS0 |tr ' ' '\n' | grep crtscts
crtscts
ubuntu@...low:~$ ls /proc/device-tree/soc/serial@...21000/has-hw-flow-control
/proc/device-tree/soc/serial@...21000/has-hw-flow-control
ubuntu@...low:~$ python
Python 2.7.6 (default, Mar 22 2014, 22:58:30)
[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> UPF_HARDWARE_FLOW = 1 << 21
>>> if 0xB9200000 & UPF_HARDWARE_FLOW:
... print "OK"
...
OK
Hope that's a reasonable test case. Test fails when booted w/o
has-hw-flow-control attribute.
Tested-by: dann frazier <dann.frazier@...onical.com>
>
> 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/Documentation/devicetree/bindings/serial/of-serial.txt b/Documentation/devicetree/bindings/serial/of-serial.txt
> index 1928a3e..7705477 100644
> --- a/Documentation/devicetree/bindings/serial/of-serial.txt
> +++ b/Documentation/devicetree/bindings/serial/of-serial.txt
> @@ -37,6 +37,7 @@ Optional properties:
> - auto-flow-control: one way to enable automatic flow control support. The
> driver is allowed to detect support for the capability even without this
> property.
> +- has-hw-flow-control: the hardware has flow control capability.
>
> Example:
>
> diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
> index 0e1bf88..b69aff2 100644
> --- a/drivers/tty/serial/8250/8250_core.c
> +++ b/drivers/tty/serial/8250/8250_core.c
> @@ -2338,9 +2338,11 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
> * the trigger, or the MCR RTS bit is cleared. In the case where
> * the remote UART is not using CTS auto flow control, we must
> * have sufficient FIFO entries for the latency of the remote
> - * UART to respond. IOW, at least 32 bytes of FIFO.
> + * UART to respond. IOW, at least 32 bytes of FIFO. Also enable
> + * AFE if hw flow control is supported
> */
> - if (up->capabilities & UART_CAP_AFE && port->fifosize >= 32) {
> + if ((up->capabilities & UART_CAP_AFE && (port->fifosize >= 32)) ||
> + (port->flags & UPF_HARD_FLOW)) {
> up->mcr &= ~UART_MCR_AFE;
> if (termios->c_cflag & CRTSCTS)
> up->mcr |= UART_MCR_AFE;
> diff --git a/drivers/tty/serial/of_serial.c b/drivers/tty/serial/of_serial.c
> index 9924660..77ec6a1 100644
> --- a/drivers/tty/serial/of_serial.c
> +++ b/drivers/tty/serial/of_serial.c
> @@ -182,6 +182,10 @@ static int of_platform_serial_probe(struct platform_device *ofdev)
> "auto-flow-control"))
> port8250.capabilities |= UART_CAP_AFE;
>
> + if (of_property_read_bool(ofdev->dev.of_node,
> + "has-hw-flow-control"))
> + port8250.port.flags |= UPF_HARD_FLOW;
> +
> ret = serial8250_register_8250_port(&port8250);
> break;
> }
> 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)) {
> if (tty->hw_stopped) {
> if (status) {
> tty->hw_stopped = 0;
> --
> 1.7.9.5
>
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