Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Thu, 10 Mar 2022 14:29:21 +0200 (EET)
From:   =?ISO-8859-15?Q?Ilpo_J=E4rvinen?= <ilpo.jarvinen@linux.intel.com>
To:     Lukas Wunner <lukas@wunner.de>
cc:     linux-serial <linux-serial@vger.kernel.org>,
        Jiri Slaby <jirislaby@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Johan Hovold <johan@kernel.org>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Heikki Krogerus <heikki.krogerus@linux.intel.com>,
        linux-api@vger.kernel.org, Richard Henderson <rth@twiddle.net>,
        Ivan Kokshaysky <ink@jurassic.park.msu.ru>,
        Matt Turner <mattst88@gmail.com>, linux-alpha@vger.kernel.org,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        linux-mips@vger.kernel.org,
        "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>,
        Helge Deller <deller@gmx.de>, linux-parisc@vger.kernel.org,
        Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        linuxppc-dev@lists.ozlabs.org,
        Yoshinori Sato <ysato@users.sourceforge.jp>,
        Rich Felker <dalias@libc.org>, linux-sh@vger.kernel.org,
        "David S. Miller" <davem@davemloft.net>,
        sparclinux@vger.kernel.org, Chris Zankel <chris@zankel.net>,
        Max Filippov <jcmvbkbc@gmail.com>,
        linux-xtensa@linux-xtensa.org, Arnd Bergmann <arnd@arndb.de>,
        linux-arch@vger.kernel.org, linux-doc@vger.kernel.org
Subject: Re: [RFC PATCH 6/7] serial: General support for multipoint
 addresses
In-Reply-To: <20220309190521.GA9832@wunner.de>
Message-ID: <6feb796a-ea58-9a6-f2f9-a11ca72acfd@linux.intel.com>
References: <20220302095606.14818-1-ilpo.jarvinen@linux.intel.com> <20220302095606.14818-7-ilpo.jarvinen@linux.intel.com> <20220306194001.GD19394@wunner.de> <ab43569c-6488-12a6-823-3ef09f2849d@linux.intel.com> <20220309190521.GA9832@wunner.de>
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="8323329-24784813-1646915371=:1973"
Precedence: bulk

  This message is in MIME format.  The first part should be readable text,
  while the remaining parts are likely unreadable without MIME-aware tools.

--8323329-24784813-1646915371=:1973
Content-Type: text/plain; charset=iso-8859-1
Content-Transfer-Encoding: 8BIT

On Wed, 9 Mar 2022, Lukas Wunner wrote:

> On Mon, Mar 07, 2022 at 11:48:01AM +0200, Ilpo J?rvinen wrote:
> > On Sun, 6 Mar 2022, Lukas Wunner wrote:
> > > On Wed, Mar 02, 2022 at 11:56:05AM +0200, Ilpo J?rvinen wrote:
> > > > This change is necessary for supporting devices with RS485
> > > > multipoint addressing [*].
> > > 
> > > If this is only used with RS485, why can't we just store the
> > > addresses in struct serial_rs485 and use the existing TIOCSRS485
> > > and TIOCGRS485 ioctls?  There's 20 bytes of padding left in
> > > struct serial_rs485 which you could use.  No need to add more
> > > user-space ABI.
> > 
> > It could if it is agreed that serial multipoint addressing is just
> > a thing in RS-485 and nowhere else? In that case, there is no point
> > in adding more generic support for it.
> 
> It's just that the above-quoted sentence in the commit message
> specifically mentions RS485.

That sentence is just to justify why addressing mode is needed,
not to take a stance on whether it is only used with RS485 or not.

> If you intend to use it with RS232
> as well, that should be made explicit, otherwise one wonders why
> it wasn't integrated into struct serial_rs485.
> 
> I have no idea how common 9th bit addressing mode is with RS232.
> Goggle turns up links saying it's mainly used with RS485, "but also
> RS232".  Since RS232 isn't a bus but a point-to-point link,
> 9th bit addressing doesn't seem to make as much sense.

While I don't know any better, I can image though that with an 
RS232-to-RS485 converter, it could make some sense.

If I put them back to serial_rs485 / rs485 config, it's basically just 
where I initially started from with this patchset (offlist).


-- 
 i.

--8323329-24784813-1646915371=:1973--