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

[Murali Karicheri <m-karicheri2@ti.com>]

On 5/28/2014 4:04 PM, Dann Frazier wrote:
> On Thu, May 1, 2014 at 1:04 PM, Murali Karicheri <m-karicheri2@ti.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@hwflow:~$ sudo stty -a --file /dev/ttyS0 |tr ' ' '\n' | grep crtscts
> crtscts
> ubuntu@hwflow:~$ ls /proc/device-tree/soc/serial@1c021000/has-hw-flow-control
> /proc/device-tree/soc/serial@1c021000/has-hw-flow-control
> ubuntu@hwflow:~$ 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@canonical.com>
What is the verdict? pass/fail? Ok/Not OK to merge?

Murali
>> Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
>>
>> CC: Rob Herring <robh+dt@kernel.org>
>> CC: Pawel Moll <pawel.moll@arm.com>
>> CC: Mark Rutland <mark.rutland@arm.com>
>> CC: Ian Campbell <ijc+devicetree@hellion.org.uk>
>> CC: Kumar Gala <galak@codeaurora.org>
>> CC: Randy Dunlap <rdunlap@infradead.org>
>> CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>> CC: Jiri Slaby <jslaby@suse.cz>
>> CC: Santosh Shilimkar <santosh.shilimkar@ti.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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