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

[Michal Simek]

On 5/2/23 12:19, Krzysztof Kozlowski wrote:
> On 02/05/2023 12:14, Guntupalli, Manikanta wrote:
> > Hi Rob Herring,
> >
> > > -----Original Message-----
> > > From: Rob Herring <robh@xxxxxxxxxx>
> > > Sent: Thursday, April 27, 2023 10:14 PM
> > > To: Guntupalli, Manikanta <manikanta.guntupalli@xxxxxxx>
> > > Cc: gregkh@xxxxxxxxxxxxxxxxxxx; krzysztof.kozlowski+dt@xxxxxxxxxx;
> > > michal.simek@xxxxxxxxxx; linux-serial@xxxxxxxxxxxxxxx;
> > > devicetree@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> > > jirislaby@xxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; Simek, Michal
> > > <michal.simek@xxxxxxx>; git (AMD-Xilinx) <git@xxxxxxx>; Pandey,
> > > Radhey Shyam <radhey.shyam.pandey@xxxxxxx>; Datta, Shubhrajyoti
> > > <shubhrajyoti.datta@xxxxxxx>; Goud, Srinivas <srinivas.goud@xxxxxxx>;
> > > manion05gk@xxxxxxxxx
> > > 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
>
> Your request for us to get into some datasheet somewhere, to get the
> answer to the basic question, is not reasonable. Commit must justify its
> existence, not some external source.

Not really. Manual itself just shows picture of that connection if you are 
interested.
On schematics it looks like that DE and /RE are just handle via one gpio. That's 
why you need 3 wires instead of 4. Definitely it should be described better.

My concern was more about choosing proper name for this functionality.

Thanks,
Michal