From: "Heiko Stübner" <heiko@sntech.de>
To: Lukas Wunner <lukas@wunner.de>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
gregkh@linuxfoundation.org, jslaby@suse.com,
matwey.kornilov@gmail.com, linux-serial@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/7] serial: 8250: Add rs485 emulation to 8250_dw
Date: Mon, 23 Mar 2020 09:25:57 +0100 [thread overview]
Message-ID: <6241816.LpgjcNKrfa@diego> (raw)
In-Reply-To: <20200319054034.dyq7yydqi6yg7jhf@wunner.de>
Hi,
Am Donnerstag, 19. März 2020, 06:40:34 CET schrieb Lukas Wunner:
> On Wed, Mar 18, 2020 at 07:49:08PM +0100, Heiko Stübner wrote:
> > Looking at tty-next I notice that you're right. When I started working
> > on this I only found the stuff from 2018 I linked to but didn't imagine
> > that in that exact moment someone else would also work on that area.
>
> There are some more patches in the pipeline for the next cycle
> to add support for an rs485 bus termination GPIO. They're on
> the tip of this branch:
>
> https://github.com/RevolutionPi/linux/commits/revpi-4.19
>
> Just so you know in advance and duplicate work is avoided.
do you plan on submitting these soonish? Because looking at your
termination-gpio change makes me want to do something similar for
my RE-gpio ... instead of trying to mangle this into the DTR thingy.
> > > The DTR-for-RE thing seems a bit nonstandard, I'm not sure if this is
> > > eligible for mainline or if it's something that should be kept in your
> > > downstream tree. But no harm in submitting it to the list.
> >
> > I'm fine either way - maybe I also get a pointer on what may be a better
> > approach ;-)
> >
> > At least DTR as "Data Terminal Ready" did sound somewhat matching for
> > the "Receive Enable" of RS485 (and it's also the only other output pin
> > in the mctrl gpio list).
>
> Some UARTs allow disabling the receiver, this can be taken advantage of
> to implement half-duplex mode. It's what I did in 8250_bcm2835aux.c.
>
> On the Revolution Pi devices, !RE is usually connected to ground, so
> reception is always enabled and it cannot be disabled in software
> except by turning off the UART receiver.
>
> There are also boards out there which connect !RE to RTS. Then only
> half-duplex mode is supported by the hardware and there's no way for
> software to work around it.
yep and on our board we have DE and RE on separate gpios, so I guess
it makes sense to use that pin how it was intended ;-) .
So I guess having that as rs485-re-gpios property might be the best way.
Heiko
next prev parent reply other threads:[~2020-03-23 8:26 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-18 14:26 [PATCH 0/7] serial: 8250: Add rs485 emulation to 8250_dw Heiko Stuebner
2020-03-18 14:26 ` [PATCH 1/7] serial: 8250: Make em485_rts_after_send() set mctrl according to rts state Heiko Stuebner
2020-03-18 14:26 ` [PATCH 2/7] serial: 8250: add serial_in_poll_timeout helper Heiko Stuebner
2020-03-18 15:09 ` Andy Shevchenko
2020-03-18 14:26 ` [PATCH 3/7] serial: 8250: Handle case port doesn't have TEMT interrupt using em485 Heiko Stuebner
2020-03-18 14:26 ` [PATCH 4/7] serial: 8250: Start rs485 after registering port if rs485 is enabled in probe Heiko Stuebner
2020-03-18 14:26 ` [PATCH 5/7] serial: 8250: handle DTR in rs485 emulation Heiko Stuebner
2020-03-18 14:26 ` [PATCH 6/7] serial: 8250_dw: add em485 support Heiko Stuebner
2020-03-18 15:15 ` Andy Shevchenko
2020-03-18 14:26 ` [PATCH 7/7] serial: 8250_dw: allow enable rs485 at boot time Heiko Stuebner
2020-03-18 15:16 ` Andy Shevchenko
2020-03-18 18:28 ` Heiko Stübner
2020-03-18 18:31 ` Heiko Stübner
2020-03-18 14:43 ` [PATCH 0/7] serial: 8250: Add rs485 emulation to 8250_dw Andy Shevchenko
2020-03-18 15:37 ` Lukas Wunner
2020-03-18 15:54 ` Andy Shevchenko
2020-03-18 18:49 ` Heiko Stübner
2020-03-19 5:40 ` Lukas Wunner
2020-03-23 8:25 ` Heiko Stübner [this message]
2020-03-23 13:17 ` Lukas Wunner
2020-03-23 13:41 ` Andy Shevchenko
2020-03-25 13:41 ` Heiko Stübner
2020-03-25 14:42 ` Andy Shevchenko
2020-03-18 15:13 ` Andy Shevchenko
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