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From:   "Guntupalli, Manikanta" <manikanta.guntupalli@amd.com>
To:     "m.brock@vanmierlo.com" <m.brock@vanmierlo.com>
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Subject: RE: [PATCH 0/2] Add rs485 support to uartps driver
Thread-Topic: [PATCH 0/2] Add rs485 support to uartps driver
Thread-Index: AQHZfoMOVvbvY/C9EUCU2o5qmO6xr69Tub0g
Date:   Wed, 10 May 2023 16:26:05 +0000
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Hi Maarten,

> -----Original Message-----
> From: m.brock@vanmierlo.com <m.brock@vanmierlo.com>
> Sent: Thursday, May 4, 2023 5:52 PM
> To: Guntupalli, Manikanta <manikanta.guntupalli@amd.com>
> Cc: gregkh@linuxfoundation.org; robh+dt@kernel.org;
> krzysztof.kozlowski+dt@linaro.org; michal.simek@xilinx.com; linux-
> serial@vger.kernel.org; devicetree@vger.kernel.org; linux-
> kernel@vger.kernel.org; jirislaby@kernel.org; linux-arm-
> kernel@lists.infradead.org; Simek, Michal <michal.simek@amd.com>; git
> (AMD-Xilinx) <git@amd.com>; Pandey, Radhey Shyam
> <radhey.shyam.pandey@amd.com>; Datta, Shubhrajyoti
> <shubhrajyoti.datta@amd.com>; Goud, Srinivas <srinivas.goud@amd.com>;
> manion05gk@gmail.com
> Subject: Re: [PATCH 0/2] Add rs485 support to uartps driver
>=20
> Manikanta Guntupalli wrote 2023-04-26 14:29:
> > Add optional gpio property to uartps node to support rs485 Add rs485
> > support to uartps driver
> >
> > Manikanta Guntupalli (2):
> >   dt-bindings: Add optional gpio property to uartps node to support
> >     rs485
> >   tty: serial: uartps: Add rs485 support to uartps driver
> >
> >  .../devicetree/bindings/serial/cdns,uart.yaml |  5 +
> >  drivers/tty/serial/xilinx_uartps.c            | 96 ++++++++++++++++++-
> >  2 files changed, 100 insertions(+), 1 deletion(-)
>=20
> Why would you want to use a GPIO and not RTS for choosing the direction a=
s
> is more common in this case?
In ZynqMp platform Cadence UART Controller RTS signal routed to external th=
rough the PL(Programmable Logic) design not through Multiplexed IO.

> And have you thought about configuring the polarity?
GPIO polarity configured through device tree property.

&uart0 {
        ...
        txrx-gpios =3D <&gpio 72 GPIO_ACTIVE_LOW>;
        linux,rs485-enabled-at-boot-time;
};

> How long will the signal be active before the real transmission begins so=
 the
> driver can settle?
Default is RE(GPIO LOW) and while sending we drive the pin to HIGH. We wait=
 for transmission completion, for that we check Transmitter state machine a=
ctive status to ZERO and TX FIFO EMPTY.=20

Thanks,
Manikanta.