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

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Date:   Thu, 14 Dec 2023 18:24:34 +0800
From:   Crescent CY Hsieh <crescentcy.hsieh@...a.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Lino Sanfilippo <LinoSanfilippo@....de>,
        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>,
        Tomas Paukrt <tomaspaukrt@...il.cz>
Subject: Re: [PATCH 1/2] dt-bindings: serial: rs485: add rs485-mux-gpios
 binding

On Mon, Dec 11, 2023 at 03:07:59PM +0200, 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.

How about revising the name of 'TIOCSRS485' and 'serial_rs485' to a
general one, and put RS422 and RS485 configuration flags into that
structure?

So that in userspace it could set RS422 or RS485 configurations using a
single ioctl command and one structure.

In this way, it won't be confused in userspace and won't add new data
structure internally as well.

---
Sincerely,
Crescent Hsieh.