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Date:   Thu, 14 Dec 2023 09:52:13 +0100
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Subject: Re: [PATCH 1/2] dt-bindings: serial: rs485: add rs485-mux-gpios
 binding
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To:     Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc:     Christoph Niedermaier <cniedermaier@dh-electronics.com>,
        Lukas Wunner <lukas@wunner.de>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jirislaby@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Conor Dooley <conor+dt@kernel.org>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-serial@vger.kernel.org" <linux-serial@vger.kernel.org>,
        =?UTF-8?Q?Ilpo_J=C3=A4rvinen?= <ilpo.jarvinen@linux.intel.com>,
        "brenda.streiff@ni.com" <brenda.streiff@ni.com>,
        Crescent CY Hsieh <crescentcy.hsieh@moxa.com>,
        Tomas Paukrt <tomaspaukrt@email.cz>
References: <20231120151056.148450-1-linux@rasmusvillemoes.dk>
 <20231120151056.148450-2-linux@rasmusvillemoes.dk>
 <20231122145344.GA18949@wunner.de>
 <3b8548b1-b8a9-0c9e-4040-5cfda06a85c6@gmx.de>
 <ec66d25162de4cbc92720df1e7008fe8@dh-electronics.com>
 <5c140498-69e3-4187-8703-db0c41e7ca89@gmx.de>
 <fe28eb93-daa1-41af-a005-f21aa87e1984@gmx.de>
 <ZXcJr4VS_uGr_6TV@smile.fi.intel.com>
From:   Lino Sanfilippo <LinoSanfilippo@gmx.de>
In-Reply-To: <ZXcJr4VS_uGr_6TV@smile.fi.intel.com>
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Precedence: bulk

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 t=
o not
> extend the existing serial data structures, we have too many ones with t=
oo many
> fields already. For user space, though, one may use unions and flags, bu=
t for
> internal ones it might be better ways, I think.
>

Ok, thanks. This is still a valuable information. So what if the above str=
ucture (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