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

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Date:   Tue, 2 May 2023 12:19:07 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     "Guntupalli, Manikanta" <manikanta.guntupalli@....com>,
        Rob Herring <robh@...nel.org>
Cc:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "michal.simek@...inx.com" <michal.simek@...inx.com>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "jirislaby@...nel.org" <jirislaby@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "Simek, Michal" <michal.simek@....com>,
        "git (AMD-Xilinx)" <git@....com>,
        "Pandey, Radhey Shyam" <radhey.shyam.pandey@....com>,
        "Datta, Shubhrajyoti" <shubhrajyoti.datta@....com>,
        "Goud, Srinivas" <srinivas.goud@....com>,
        "manion05gk@...il.com" <manion05gk@...il.com>
Subject: Re: [PATCH 1/2] dt-bindings: Add optional gpio property to uartps
 node to support rs485

On 02/05/2023 12:14, Guntupalli, Manikanta wrote:
> Hi Rob Herring,
> 
>> -----Original Message-----
>> From: Rob Herring <robh@...nel.org>
>> Sent: Thursday, April 27, 2023 10:14 PM
>> To: Guntupalli, Manikanta <manikanta.guntupalli@....com>
>> Cc: gregkh@...uxfoundation.org; krzysztof.kozlowski+dt@...aro.org;
>> michal.simek@...inx.com; linux-serial@...r.kernel.org;
>> devicetree@...r.kernel.org; linux-kernel@...r.kernel.org;
>> jirislaby@...nel.org; linux-arm-kernel@...ts.infradead.org; Simek, Michal
>> <michal.simek@....com>; git (AMD-Xilinx) <git@....com>; Pandey,
>> Radhey Shyam <radhey.shyam.pandey@....com>; Datta, Shubhrajyoti
>> <shubhrajyoti.datta@....com>; Goud, Srinivas <srinivas.goud@....com>;
>> manion05gk@...il.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

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.

> 
>>
>>>
>>> Signed-off-by: Manikanta Guntupalli <manikanta.guntupalli@....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.

It's not about explaining it here, but making your changes justified and
obvious once implemented.

Best regards,
Krzysztof