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

[Lino Sanfilippo]

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@xxxxxxxx/
>>>>>>
>>>>>
>>>>> 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