Re: [PATCH 1/4] serial: 8250: Copy em485 from port to real port.

[Giulio Benetti]

Il 06/06/2018 20:55, Matwey V. Kornilov ha scritto:
> 2018-06-06 16:11 GMT+03:00 Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>:
> > On Wed, 2018-06-06 at 14:15 +0200, Giulio Benetti wrote:
> > > Il 06/06/2018 13:56, Andy Shevchenko ha scritto:
> > > > On Wed, 2018-06-06 at 11:49 +0200, Giulio Benetti wrote:
> > > > > em485 gets lost during
> > > > >
> > > > > Copy em485 to final uart port.
> > > >
> > > > Is it needed at all?
> > > >
> > > > The individual driver decides either to use software emulation (and
> > > > calls explicitly serial8250_em485_init() for that) or do HW assisted
> > > > stuff.
> > >
> > > In 8250_dw.c, during probe(), I need to call dw8250_rs485_config()
> > > against local struct uart_8250_port uart = {};
> > > Inside serial8250_register_8250_port() not all uart fields are
> > > copied(em485 too).
> > > So after probe, em485 is NULL.
> > >
> > > Another way could be to call dw8250_rs485_config() against real uart
> > > port, after calling serial8250_register_8250_port(),
> > > would it make sense?
> >
> > Look at OMAP case closely. They have a callback to configure RS485 which
> > is called in uart_set_rs485_config()  which is called whenever user
> > space does TIOCGRS485 IOCTL.
> >
> > So, it's completely driven by user space which makes sense by my
> > opinion.
>
> AFAIU, Giulio wants to add support for rs485-enabled-at-boot-time
> device tree option (see bindings/serial/rs485.txt for reference).

Yes, I want to add support for "rs485-enabled-at-boot-time" property,
maybe I had to write better commit log and a cover letter. Sorry.

> I suppose it is only important for use-case when rs485 used as slave
> (peripheral role).

It's important also for master, because RTS, if RTS_AFTER_SEND is set, 
remains not asserted(trasnmission) until userspace opens that serial port.

Sorry again for not explaining myself well.

--
Giulio Benetti
CTO

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