[PATCH 1/2] dt-bindings: Add optional gpio property to uartps node to support rs485

[Guntupalli, Manikanta]

Hi Rob Herring,

> -----Original Message-----
> From: Rob Herring <robh at kernel.org>
> Sent: Thursday, April 27, 2023 10:14 PM
> To: Guntupalli, Manikanta <manikanta.guntupalli at amd.com>
> Cc: gregkh at linuxfoundation.org; krzysztof.kozlowski+dt at linaro.org;
> michal.simek at xilinx.com; linux-serial at vger.kernel.org;
> devicetree at vger.kernel.org; linux-kernel at vger.kernel.org;
> jirislaby at kernel.org; linux-arm-kernel at lists.infradead.org; Simek, Michal
> <michal.simek at amd.com>; git (AMD-Xilinx) <git at amd.com>; Pandey,
> Radhey Shyam <radhey.shyam.pandey at amd.com>; Datta, Shubhrajyoti
> <shubhrajyoti.datta at amd.com>; Goud, Srinivas <srinivas.goud at amd.com>;
> manion05gk at gmail.com
> Subject: Re: [PATCH 1/2] dt-bindings: Add optional gpio property to uartps
> node to support rs485
> 
> On Wed, Apr 26, 2023 at 05:59:46PM +0530, Manikanta Guntupalli wrote:
> > Add optional gpio property to uartps node and add reference to rs485.yaml
> 
> The diff tells me that already. Why?
Please check Figure 11-3 (Page number 37) in the below mentioned data sheet, It shows PMOD (ISOW14x2) devices used in half duplex configuration. Driver outputs Y and Z are shorted to A and B respectively. This reduces overall cabling requirements. Also DE/RE are shorted to each other, and at a time, any node acts as either a driver or a receiver.
Using above optional GPIO controlling driver or a receiver. This GPIO is optional because it is not required for uart console node.

Here,
DE - Driver enable. If pin is floating, driver is disabled (internal pull-down resistor)
RE - Receiver enable. If pin is floating, receiver buffer is disabled (internal pull-up resistor)

Datasheet:
https://www.ti.com/lit/ds/symlink/isow1432.pdf?ts=1682607122706&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FISOW1432%252Fpart-details%252FISOW1432DFMR%253FkeyMatch%253DISOW1432DFMR%2526tisearch%253Dsearch-everything%2526usecase%253DOPN

> 
> >
> > Signed-off-by: Manikanta Guntupalli <manikanta.guntupalli at amd.com>
> > ---
> >  Documentation/devicetree/bindings/serial/cdns,uart.yaml | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/serial/cdns,uart.yaml
> b/Documentation/devicetree/bindings/serial/cdns,uart.yaml
> > index a8b323d7bf94..34ed0d80b923 100644
> > --- a/Documentation/devicetree/bindings/serial/cdns,uart.yaml
> > +++ b/Documentation/devicetree/bindings/serial/cdns,uart.yaml
> > @@ -46,6 +46,10 @@ properties:
> >    power-domains:
> >      maxItems: 1
> >
> > +  txrx-gpios:
> > +    description: Optional GPIO to switch transmit and receive modes via
> pmod.
> 
> What's pmod?
Pmod is galvanically-isolated RS-485/RS-422 transceivers with a built-in isolated
DC-DC converter, that eliminates the need for a separate isolated power supply in
space constrained isolated designs.

> 
> > +    maxItems: 1
> > +
> >  required:
> >    - compatible
> >    - reg
> > @@ -55,6 +59,7 @@ required:
> >
> >  allOf:
> >    - $ref: serial.yaml#
> > +  - $ref: rs485.yaml#
> >    - if:
> >        properties:
> >          compatible:
> > --
> > 2.25.1
> >