linux-kernel - Re: [PATCH] Stop pmac_zilog from abusing 8250's device numbers.

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Date:	Wed, 4 Apr 2007 15:53:50 +1000
From:	Paul Mackerras <paulus@...ba.org>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Brad Boyer <flar@...andria.com>, linuxppc-dev@...abs.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Stop pmac_zilog from abusing 8250's device numbers.

David Woodhouse writes:

> Why? What's so special about the name 'ttyS'?

It's the name that users of Linux expect built-in serial ports to have.

> > The built-in ports can generally be enumerated early on boot in a
> > stable order, and they should be assigned the low ttySn numbers,
> > regardless of what chip is used to implement them. 
> 
> I don't see why that 'should' be the case. Certainly it _isn't_ the case
> on most supported platforms -- we have separate device numbers, and
> names, for most types of ports. There's only one or two drivers which
> abuse ttySn for anything other than 8250 ports.

It 'should' be the case because that is what is easiest for users and
makes most sense from a user's point of view.

You still haven't given any reason why a user should have to know or
care whether the built-in serial ports on his/her computer are
implemented with a 16C550 chip or a Z85C30 chip or something else.

Now, *maybe* the naming can be fixed up with udev.  I haven't invested
the week of my life that it would take to investigate the twisty maze
of shell scripts that udev seems to involve.

In any case your patch is a user-visible incompatible API change and
will break existing working setups, so it should only be put in after
suitable warning has been given.  Maybe we need a module parameter to
select between the old and new behaviour to ease the transition.

Paul.
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