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

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Date:	Wed, 4 Apr 2007 19:15:32 +0100
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	Theodore Tso <tytso@....edu>, "H. Peter Anvin" <hpa@...or.com>,
	David Miller <davem@...emloft.net>, dwmw2@...radead.org,
	paulus@...ba.org, alan@...rguk.ukuu.org.uk, flar@...andria.com,
	linuxppc-dev@...abs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Stop pmac_zilog from abusing 8250's device numbers.

On Wed, Apr 04, 2007 at 01:41:53PM -0400, Theodore Tso wrote:
> On Wed, Apr 04, 2007 at 09:16:42AM -0700, H. Peter Anvin wrote:
> > One option would be to move the 8250-based serial ports, to, say, 
> > /dev/ttyN* (for National Semiconductors -- the best I could come up 
> > with) and redefine /dev/ttyS* as a serial port multiplexer which maps in 
> > all the types, for the ones that really want dynamic mapping.
> 
> > Of course, now you have the potential of aliasing, again, which tends to 
> > cause all kinds of headaches w.r.t. locking.  
> 
> That would break the 99.9% of the the world using Intel-based systems
> which only have 8250's, for very little gain. 
> 
> Like it or not, /dev/ttySx and 8250 UART's are to serial ports what
> the PCI is to system buses....

And the simple answer to this (oh I've been here before) is to leave
the existing serial allocations well alone.

Then, you allocate a new major number and device name for the dynamically
assigned space and arrange for the serial layer to map these new chardevs
to the real serial ports.

*However* you still run into the issue that you do not know how many
serial ports you will need to register a tty driver with the tty layer.
Solve that technical problem and the idea of having a single namespace
for chosen serial ports and 8250 ports suddenly becomes realistic.

Continue ignoring that problem and this thread will just grow with zero
real progress.

I'm repeating myself though.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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