linux-kernel - Re: [RFC] serial: sc16is7xx: Use DT sub-nodes for UART ports

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Date:   Fri, 10 Aug 2018 12:11:41 -0600
From:   Rob Herring <robh@...nel.org>
To:     Andreas Färber <afaerber@...e.de>
Cc:     "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Linux-MIPS <linux-mips@...ux-mips.org>, jringle@...dpoint.com,
        Michael Allwright <allsey87@...il.com>,
        Jakub Kicinski <kubakici@...pl>, liuxuenetmail@...il.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] serial: sc16is7xx: Use DT sub-nodes for UART ports

On Fri, Aug 10, 2018 at 11:45 AM Andreas Färber <afaerber@...e.de> wrote:
>
> Am 10.08.2018 um 19:34 schrieb Rob Herring:
> > On Sun, Aug 5, 2018 at 5:27 PM Andreas Färber <afaerber@...e.de> wrote:
> >>
> >> This is to allow using serdev.
> >>
> >> Signed-off-by: Andreas Färber <afaerber@...e.de>
> >> ---
> >>  drivers/tty/serial/sc16is7xx.c | 25 +++++++++++++++++++++++++
> >>  1 file changed, 25 insertions(+)
> >>
> >> diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
> >> index 243c96025053..ad7267274f65 100644
> >> --- a/drivers/tty/serial/sc16is7xx.c
> >> +++ b/drivers/tty/serial/sc16is7xx.c
> >> @@ -1213,9 +1213,31 @@ static int sc16is7xx_probe(struct device *dev,
> >>                         SC16IS7XX_IOCONTROL_SRESET_BIT);
> >>
> >>         for (i = 0; i < devtype->nr_uart; ++i) {
> >> +#ifdef CONFIG_OF
> >> +               struct device_node *np;
> >> +               struct platform_device *pdev;
> >> +               char name[6] = "uartx";
> >> +#endif
> >> +
> >>                 s->p[i].line            = i;
> >>                 /* Initialize port data */
> >> +#ifdef CONFIG_OF
> >> +               name[4] = '0' + i;
> >> +               np = of_get_child_by_name(dev->of_node, name);
> >> +               if (IS_ERR(np)) {
> >> +                       ret = PTR_ERR(np);
> >> +                       goto out_ports;
> >> +               }
> >> +               pdev = of_platform_device_create(np, NULL, dev);
> >
> > Ideally, you would use of_platform_default_populate here. I think
> > you'd have to add a compatible to the child nodes, but that wouldn't
> > be a bad thing. I could envision that the child nodes ultimately
> > become their own driver utilizing the standard 8250 driver and a
> > compatible string would be needed in that case.
>
> Separate compatibles would mean separate drivers.

No. Having a compatible doesn't mean you have to have a driver.

> Unlike your DUART example this is not an MMIO device that we can easily
> split but a SPI slave (well, regmap due to some I2C models).

A SPI slave could provide a regmap, right?

> I don't see how separate drivers could work, given that the whole
> spi_device has a single interrupt for all functions of this device.

A shared interrupt or a parent driver that creates an irqchip like MFD
drivers often do.

>
> That left me with this ugly but working construct.

In any case, I'm was suggesting that you do any of this now. I just
want the binding to be designed to work either way.

> Is the uartX naming correct, or should it be serialX?

Ah, yes. Should be serial@... I'm fine if both the parent and child
are named serial@...

Rob