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

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Date:   Thu, 14 Dec 2023 09:52:13 +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,

On 11.12.23 14:07, Andy Shevchenko wrote:
> On Sat, Dec 09, 2023 at 12:47:47PM +0100, Lino Sanfilippo wrote:
>> On 06.12.23 16:42, Lino Sanfilippo wrote:
>
>>>>>> Crescent CY Hsieh (+cc) is in parallel trying to add an RS-422 mode bit
>>>>>> to struct serial_rs485:
>>>>>>
>>>>>> https://lore.kernel.org/all/20231121095122.15948-1-crescentcy.hsieh@moxa.com/
>>>>>>
>>>>>
>>>>> That new flag was suggested by me instead of using SER_RS422_ENABLED, which
>>>>> would mostly be redundant to SER_RS485_ENABLED.
>>
>> A cleaner solution would probably be to not handle RS422 with the RS485 settings at
>> all, but to introduce another set of ioctls to set and read it.
>>
>> An own RS422 structure like
>>
>> struct serial_rs422 {
>> 	__u32	flags;
>> #define SER_RS422_ENABLED		(1 << 0)
>> #define SER_RS422_TERMINATE_BUS		(1 << 1)
>> };
>>
>>
>> could be used as the parameter for these new ioctls.
>>
>> Any comments on this?
>
> I have (maybe not so constructive) a comment. Please, at all means try to not
> extend the existing serial data structures, we have too many ones with too many
> fields already. For user space, though, one may use unions and flags, but for
> internal ones it might be better ways, I think.
>

Ok, thanks. This is still a valuable information. So what if the above structure (serial_rs422)
is only used as a parameter of a new TIOCSRS422 ioctl and only internally we set a SER_RS485_MODE_RS422
flag in the serial_rs485 struct?
So we do not have to add something new to uart_port but also do not expose the mixture of RS485 and RS422
settings within the serial_rs485 structure to userspace.

Regards,
Lino