linux-kernel - Re: [PATCH] serial: DCC(JTAG) serial and console emulation support

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Message-ID: <1286484678.23836.49.camel@c-dwalke-linux.qualcomm.com>
Date:	Thu, 07 Oct 2010 13:51:18 -0700
From:	Daniel Walker <dwalker@...eaurora.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	linux-kernel@...r.kernel.org,
	"Hyok S. Choi" <hyok.choi@...sung.com>,
	Tony Lindgren <tony@...mide.com>,
	Jeff Ohlstein <johlstei@...cinc.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Ben Dooks <ben-linux@...ff.org>,
	Alan Cox <alan@...ux.intel.com>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Mike Frysinger <vapier@...too.org>,
	Feng Tang <feng.tang@...el.com>,
	Tobias Klauser <tklauser@...tanz.ch>,
	Jason Wessel <jason.wessel@...driver.com>,
	Philippe Langlais <philippe.langlais@...ricsson.com>
Subject: Re: [PATCH] serial: DCC(JTAG) serial and console emulation support

On Thu, 2010-10-07 at 22:05 +0100, Alan Cox wrote:
> On Thu, 07 Oct 2010 13:36:06 -0700
> Daniel Walker <dwalker@...eaurora.org> wrote:
> 
> > On Thu, 2010-10-07 at 21:50 +0100, Alan Cox wrote:
> > > > +	  Say Y here if you want to install DCC driver as a normal serial port
> > > > +	  /dev/ttyS0 (major 4, minor 64). Otherwise, it appears as /dev/ttyJ0
> > > > +	  (major 4, minor 128) and can co-exist with other UARTs, such as
> > > > +	  8250/16C550 compatibles.
> > > > +
> > > 
> > > NAK to both
> > 
> > Both what?
> 
> Both device allocations. Please use the 204,186 assigned for JTAG DCC.
> 
> > I would agree if this wasn't strictly for debugging embedded devices in
> > difficult situations.. After talking to Mike, it's seems like it would
> > be useful to have this as a ttyS* specifically because embedded devices
> > won't always create a ttyJ* for you and ttyS* will likely already exist.
> 
> If you are debugging an embedded device you are capable of changing it
> (otherwise you wouldn't debug it). Therefore the fact you might need to
> tweak the tty creation on the device is not a problem. If you can't
> change the device well there is no point debugging it is there !

Your making too many assumptions .. You might be able to modify the
kernel, and not the userspace. So you couldn't tweak the device
creation .. It's much easier in the server world ..

Hyok should really be addressing this .. If he added for some random
useless reason , then for sure we can rip it out .. Otherwise I think it
deserves some more discussion ..

> We've said no over a period of about ten years to a lot of attempts to
> just borrow the ttyS0 range. If we'd said yes it would have been a
> complete mess by now.
> 
> So the answer is no.

Nothing can be unilateral, there's always room for exceptions. You
should say something more like "it's possible, but unlikely".

Daniel

-- 

Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

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