linux-kernel - Re: [STLinux Kernel] [PATCH 2/3] serial: st-asc: Provide RTS functionality

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Date:   Tue, 6 Dec 2016 12:31:31 +0000
From:   Peter Griffin <peter.griffin@...aro.org>
To:     Patrice Chotard <patrice.chotard@...com>
Cc:     Lee Jones <lee.jones@...aro.org>, gregkh@...uxfoundation.org,
        jslaby@...e.com, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kernel@...inux.com
Subject: Re: [STLinux Kernel] [PATCH 2/3] serial: st-asc: Provide RTS
 functionality

Hi Lee,

On Mon, 05 Dec 2016, Patrice Chotard wrote:

> Hi Lee
> 
> On 12/02/2016 03:11 PM, Lee Jones wrote:
> > Until this point, it has not been possible for serial applications
> > to toggle the UART RTS line.  This can be useful with certain
> > configurations. For example, when using a Mezzanine on a Linaro
> > 96board, RTS line is used to take the the on-board microcontroller
> 
> typo "the the on"
> 
> > in and out of reset.
> > 
> > Signed-off-by: Lee Jones <lee.jones@...aro.org>
> > ---
> >  drivers/tty/serial/st-asc.c | 14 ++++++++++++++
> >  1 file changed, 14 insertions(+)
> > 
> > diff --git a/drivers/tty/serial/st-asc.c b/drivers/tty/serial/st-asc.c
> > index 379e5bd..ce46898 100644
> > --- a/drivers/tty/serial/st-asc.c
> > +++ b/drivers/tty/serial/st-asc.c
> > @@ -30,6 +30,7 @@
> >  #include <linux/of_platform.h>
> >  #include <linux/serial_core.h>
> >  #include <linux/clk.h>
> > +#include <linux/gpio/consumer.h>
> >  
> >  #define DRIVER_NAME "st-asc"
> >  #define ASC_SERIAL_NAME "ttyAS"
> > @@ -38,6 +39,7 @@
> >  
> >  struct asc_port {
> >  	struct uart_port port;
> > +	struct gpio_desc *rts;
> >  	struct clk *clk;
> >  	unsigned int hw_flow_control:1;
> >  	unsigned int force_m1:1;
> > @@ -381,12 +383,16 @@ static unsigned int asc_tx_empty(struct uart_port *port)
> >  
> >  static void asc_set_mctrl(struct uart_port *port, unsigned int mctrl)
> >  {
> > +	struct asc_port *ascport = to_asc_port(port);
> > +
> >  	/*
> >  	 * This routine is used for seting signals of: DTR, DCD, CTS/RTS
> >  	 * We use ASC's hardware for CTS/RTS, so don't need any for that.
> >  	 * Some boards have DTR and DCD implemented using PIO pins,
> >  	 * code to do this should be hooked in here.
> >  	 */
> > +
> > +	gpiod_set_value(ascport->rts, mctrl & TIOCM_RTS);

This now puts the code and the comment above out of sync with each
other.

However just checking the stih410 datasheet and I don't think this patch
to control RTS via a GPIO is required anyway.

The correct way of handling this is to add UART10_RTS and UART10_CTS pins
to the pinctrl_serial0 group so they are properly configured for their cts/rts
alternate function. Once the pins are correctly configured, the IP block should
control the signals correctly like the comment says.

regards,

Peter.