linux-kernel - Re: [PATCH 3/3 v6] tty/serial/8250: use mctrl

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Date:   Mon, 17 Jun 2019 14:51:15 +0200
From:   Yegor Yefremov <yegorslists@...glemail.com>
To:     Stefan Roese <sr@...x.de>
Cc:     linux-serial@...r.kernel.org,
        kernel list <linux-kernel@...r.kernel.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Giulio Benetti <giulio.benetti@...ronovasrl.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 3/3 v6] tty/serial/8250: use mctrl_gpio helpers

On Mon, Jun 17, 2019 at 2:42 PM Stefan Roese <sr@...x.de> wrote:
>
> On 17.06.19 11:51, Yegor Yefremov wrote:
>
> <snip>
>
> >>> @@ -1944,11 +1948,15 @@ unsigned int serial8250_do_get_mctrl(struct uart_port *port)
> >>>   {
> >>>          struct uart_8250_port *up = up_to_u8250p(port);
> >>>          unsigned int status;
> >>> +       unsigned int val = 0;
> >>>
> >>>          serial8250_rpm_get(up);
> >>>          status = serial8250_modem_status(up);
> >>>          serial8250_rpm_put(up);
> >>>
> >>> +       if (up->gpios)
> >>> +               return mctrl_gpio_get(up->gpios, &val);
> >>> +
> >>
> >> What happens when you have a mixed setup i.e. CTS controlled by UART
> >> but other status pins controlled by GPIO? In this case CTS status
> >> won't be returned. Do I see it right?
>
> Yes, your analysis does seem to be correct. Please note that I did
> not intentionally did change it this way. I was not thinking about
> such a "mixed design".
>
> > What about something like this:
> >
> > unsigned int serial8250_do_get_mctrl(struct uart_port *port)
> >    {
> >            struct uart_8250_port *up = up_to_u8250p(port);
> >            unsigned int status;
> >            unsigned int val;
> >
> >            serial8250_rpm_get(up);
> >            status = serial8250_modem_status(up);
> >            serial8250_rpm_put(up);
> >
> >            val = serial8250_MSR_to_TIOCM(status);
> >            if (up->gpios)
> >                    mctrl_gpio_get(up->gpios, &val);
> >
> >            return val;
> >    }
>
> Looks good to me, thanks. Do you have such a setup with some modem
> control signal handled via GPIO and some via the UART? Could you
> test such a change?

I already have :-)

This my DTS file:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/am335x-baltos-ir5221.dts#n38

Yegor