Date: Wed, 8 May 2013 12:45:12 -0400 (EDT)
From: Nicolas Pitre <nicolas.pitre@linaro.org>
To: Arnd Bergmann <arnd@arndb.de>
cc: Greg KH <gregkh@linuxfoundation.org>,
        Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>,
        Srinivas KANDAGATLA <srinivas.kandagatla@st.com>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Will Deacon <will.deacon@arm.com>, jslaby@suse.cz,
        Russell King <linux@arm.linux.org.uk>,
        Samuel Ortiz <sameo@linux.intel.com>, linux-doc@vger.kernel.org,
        Stephen Gallimore <stephen.gallimore@st.com>,
        linux-serial@vger.kernel.org, Jason Cooper <jason@lakedaemon.net>,
        devicetree-discuss@lists.ozlabs.org,
        Rob Herring <rob.herring@calxeda.com>,
        Stuart Menefy <stuart.menefy@st.com>,
        Stephen Warren <swarren@nvidia.com>,
        Dong Aisheng <dong.aisheng@linaro.org>,
        linux-arm-kernel@lists.infradead.org,
        Mark Brown <broonie@opensource.wolfsonmicro.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [RFC 1/8] serial:st-asc: Add ST ASC driver.
In-Reply-To: <201305081831.48566.arnd@arndb.de>
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On Wed, 8 May 2013, Arnd Bergmann wrote:

> On Wednesday 08 May 2013, Greg KH wrote:
> > > just mention there is not hardware reason to not use the generic ttySx
> > > in place of ttyAS as we have only one IP that handle serial on this
> > > family of SoC
> > > 
> > > personally I'll switch to ttySx
> > 
> > Great, then you can use the same major/minor range as well, so there's
> > no more objection from me about this :)
> 
> Does that work these days when you have kernel with multiple built-in
> uart drivers?
> 
> I think it would be good if all uarts were using the same name space
> and major/minor numbers, but I think the mess we currently have is
> the result of the tty_register_driver() interface reserving the
> device number range at driver load time, independent of the presence
> of devices.  I would assume that normal distro kernels always ship
> with an 8250 driver built-in to allow using that as the console,
> and if I read the code correctly, that currently prevents another
> uart driver from registering the same major/minor numbers.

I tried to fix this up over 10 years ago.  RMK tried as well. This 
failed because X86 people insisted on always having COM1 as /dev/ttyS0, 
COM3 as /dev/ttyS2 and so on, even when some of them weren't present.

A common and dynamic namespace eventually succeeded for hard disks.
Maybe people are ready to accept it for serial ports as well now?


Nicolas
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