linux-kernel - Re: PNPACPI probes serial twice, messes up serial console

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Message-ID: <20070324100614.GA13764@flint.arm.linux.org.uk>
Date:	Sat, 24 Mar 2007 10:06:14 +0000
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	Bjorn Helgaas <bjorn.helgaas@...com>
Cc:	Keith Owens <kaos@....com.au>, linux-kernel@...r.kernel.org,
	len.brown@...el.com, Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: PNPACPI probes serial twice, messes up serial console

On Wed, Mar 21, 2007 at 10:40:54AM -0600, Bjorn Helgaas wrote:
> On Wednesday 21 March 2007 10:37, Russell King wrote:
> > On Wed, Mar 21, 2007 at 10:35:38AM -0600, Bjorn Helgaas wrote:
> > > On Tuesday 20 March 2007 08:32, Bjorn Helgaas wrote:
> > > > On Tuesday 20 March 2007 00:46, Keith Owens wrote:
> > > > > Booting with 'console=tty console=ttyS0,9600'.  The serial console on
> > > > > ttyS0 (0x3f8, irq 4) is probed twice, once from serial8250_init() and
> > > > > again from serial_pnp_probe().
> > > > 
> > > > I played with this last summer, but was too timid to finish it
> > > > and post it.  My plan was to remove the legacy SERIAL_PORT_DFNS,
> > > > make platform devices for them, and only register the platform
> > > > devices in the absence of PNP.
> > > > 
> > > > My motivation at the time was to prevent 8250 from claiming IRDA
> > > > devices that happened to live at legacy UART addresses.  I also
> > > > wanted to make IRDA (smsc-ircc2 in my case) smart enough to use
> > > > PNP to locate its devices, since 8250 would no longer claim them.
> > > > 
> > > > Here's the dusty patch (against 2.6.18-rc1-mm2).  If it seems
> > > > like a reasonable thing to do, I can update it, polish it up,
> > > > add a changelog, and post it.
> > > 
> > > Keith, does this patch help?  Russell didn't complain about it, so
> > > if it fixes your problem, maybe we could put it in -mm and see if
> > > it breaks anything else.
> > 
> > Yes I did.
> 
> Sorry.  What I should have said was "Russell gave constructive
> feedback for a minor improvement, but didn't complain about the
> overall approach of converting to platform devices, so if the
> patch solves your (Keith's) problem, I'll incorporate Russell's
> feedback and send an updated patch to Andrew."

I did also point out that the autoconfig should be transparent, and if
it isn't there's probably a bug in there somewhere.

So I partly view this patch as a papering over of the real problem, but
for other reasons it's more or less the right direction for stuff to go.
Except that the x86 definitions should be in arch/i386 rather than
drivers/serial, like the other architectures which have been converted
to this model already do.

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