linux-kernel - Re: [PATCH v3 10/15] serial: stm32-usart: Add STM32 USART Driver

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Date:	Fri, 27 Mar 2015 13:30:07 +0100
From:	Maxime Coquelin <mcoquelin.stm32@...il.com>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Andreas Färber <afaerber@...e.de>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Rob Herring <robh+dt@...nel.org>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Linus Walleij <linus.walleij@...aro.org>,
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	Peter Meerwald <pmeerw@...erw.net>,
	Paul Bolle <pebolle@...cali.nl>,
	Jonathan Corbet <corbet@....net>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Russell King <linux@....linux.org.uk>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
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Subject: Re: [PATCH v3 10/15] serial: stm32-usart: Add STM32 USART Driver

2015-03-27 12:32 GMT+01:00 Peter Hurley <peter@...leysoftware.com>:
> On 03/26/2015 06:03 PM, Maxime Coquelin wrote:
>>>> +static void stm32_set_termios(struct uart_port *port, struct ktermios *termios,
>>>> +                         struct ktermios *old)
>>>> +{
>>>> +     unsigned int baud;
>>>> +     u32 usardiv, mantissa, fraction;
>>>> +     tcflag_t cflag;
>>>> +     u32 cr1, cr2, cr3;
>>>> +     unsigned long flags;
>>>> +
>>>> +     baud = uart_get_baud_rate(port, termios, old, 0, port->uartclk / 16);
>>>> +     cflag = termios->c_cflag;
>>>> +
>>>> +     spin_lock_irqsave(&port->lock, flags);
>>>> +
>>>> +     /* Stop serial port and reset value */
>>>> +     writel_relaxed(0, port->membase + USART_CR1);
>>>> +
>>>> +     cr1 = USART_CR1_TE | USART_CR1_RE | USART_CR1_UE | USART_CR1_RXNEIE;
>>>> +
>>>> +     if (cflag & CSTOPB)
>>>> +             cr2 = USART_CR2_STOP_2B;
>>>> +
>>>> +     if (cflag & PARENB) {
>>>> +             cr1 |= USART_CR1_PCE;
>>>> +             if ((cflag & CSIZE) == CS8)
>>>> +                     cr1 |= USART_CR1_M;
>>>> +     }
>>>> +
>>>> +     if (cflag & PARODD)
>>>> +             cr1 |= USART_CR1_PS;
>>>> +
>>>> +     if (cflag & CRTSCTS)
>>>> +             cr3 = USART_CR3_RTSE | USART_CR3_CTSE;
>>>
>>> If this means autoflow control, then you need to define
>>> throttle()/unthrottle() methods, otherwise the serial core won't
>>> be able to throttle the remote when input buffers are about
>>> to overflow.
>>>
>>> And you should only enable the autoCTS and let the serial
>>> core enable autoRTS through set_mctrl(TIOCM_RTS).
>>>
>>> Just let me know if you need more info about how to do this.
>>
>> Ok, let's see if I have well understood.
>>
>> USART_CR3_RTSE should be set/cleared in set_mctrl(), depending on
>> TIOCM_RTS  value.
>> The throttle callback should disable the rx interrupt, and the
>> unthrottle enable it.
>> For CTS, it should be enabled in set_termios() if CRTSCTS, as done here.
>>
>> Am I right?
>
> Yeah, basically. You also have to indicate to the serial core that you
> require throttle/unthrottle handling in this mode by setting port->status.
>
> Your set_termios() method would look like:
>
>         port->status &= ~(UPSTAT_AUTOCTS | UPSTAT_AUTORTS);
>         if (cflag & CRTSCTS) {
>                 port->status |= UPSTAT_AUTOCTS | UPSTAT_AUTORTS;
>                 cr3 = USART_CR3_CTSE;
>         }
>
> and your set_mctrl() method would look like:
>
>         if ((mctrl & TIOCM_RTS) && (port->status & UPSTAT_AUTORTS))
>                 stm32_set_bits(port, USART_CR3, USART_CR3_RTSE);
>         else
>                 stm32_clear_bits(port, USART_CR3, USART_CR3_RTSE);
>
> The UPSTAT_AUTOCTS doesn't really do anything right now but please
> use it anyway to indicate this driver has that functionality.

Ok, thanks for your support.

I will implement this in the v4.

Regards,
Maxime

>
> Regards,
> Peter Hurley
>
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