linux-kernel - Re: [PATCH 1/2] dt-bindings: serial: rs485: add rs485-mux-gpios binding

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Date:   Sat, 9 Dec 2023 12:24:48 +0100
From:   Lino Sanfilippo <LinoSanfilippo@....de>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Christoph Niedermaier <cniedermaier@...electronics.com>,
        Lukas Wunner <lukas@...ner.de>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        "brenda.streiff@...com" <brenda.streiff@...com>,
        Crescent CY Hsieh <crescentcy.hsieh@...a.com>,
        Tomas Paukrt <tomaspaukrt@...il.cz>
Subject: Re: [PATCH 1/2] dt-bindings: serial: rs485: add rs485-mux-gpios
 binding

Hi Andy,

On 07.12.23 13:35, Andy Shevchenko wrote:
> On Wed, Dec 06, 2023 at 04:42:53PM +0100, Lino Sanfilippo wrote:
>> On 27.11.23 13:14, Christoph Niedermaier wrote:
>>> From: Lino Sanfilippo [mailto:LinoSanfilippo@....de]
>>> Sent: Sunday, November 26, 2023 12:40 AM
>
> ...
>
>>> RS-485 (2-wire NO RX_DURING_TX): rs485->flags = SER_RS485_ENABLED|SER_RS485_MODE_HALF_DUPLEX
>>> RS-485 (2-wire RX_DURING_TX):    rs485->flags = SER_RS485_ENABLED|SER_RS485_MODE_HALF_DUPLEX|SER_RS485_RX_DURING_TX
>>
>> I think we can omit the SER_RS485_MODE_HALF_DUPLEX flag if we assume that
>> a missing SER_RS485_MODE_FULL_DUPLEX means half duplex (i.e. controlling
>> the RTS line).
>
> You should be very careful on these assumptions, i.e. one must to check _all_
> existing user space tools (at least that are in use / supplied by main distros)
> on how they behave.
>

Until now the DUPLEX flags do not yet exist, so existing userspace applications are not
concerned. Christoph suggested to introduce two flags to distinguish between
a FULL duplex and a half duplex RS485 mode. My point was that we  do not need the flag
for half duplex, since this would be the default.

BR,
Lino