linux-kernel - Re: commit 7e92b4fc34 - x86, serial: convert legacy COM ports to platform devices

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Date:	Wed, 25 Jul 2007 15:38:39 +0200
From:	Sébastien Dugué <sebastien.dugue@...l.net>
To:	Sébastien Dugué <sebastien.dugue@...l.net>
Cc:	Bjorn Helgaas <bjorn.helgaas@...com>,
	linux-kernel <linux-kernel@...r.kernel.org>, ambx1@....rr.com,
	akpm@...ux-foundation.org, lenb@...nel.org, rmk@....linux.org.uk,
	mjg59@...f.ucam.org, castet.matthieu@...e.fr, shaohua.li@...el.com
Subject: Re: commit 7e92b4fc34 - x86, serial: convert legacy COM ports to
 platform devices - broke my serial console

On Wed, 25 Jul 2007 15:32:53 +0200 Sébastien Dugué <sebastien.dugue@...l.net> wrote:

> 
>   Hi Bjorn,
> 
> On Wed, 25 Jul 2007 07:16:44 -0600 Bjorn Helgaas <bjorn.helgaas@...com> wrote:
> 
> > On Wednesday 25 July 2007 01:45:54 am Sébastien Dugué wrote:
> > >   looks like the commit was dropped, nevertheless here is some more info
> > > to try and understand what may be going on so it may benefit the posterity ;-)
> > 
> > Thank you very much.
> > 
> > Your machine does indeed describe both UARTs in ACPI, and the PNP probe
> > finds them correctly.  The only wrinkle is that the PNP probe names the
> > ports in the order they appear in the ACPI namespace, and your firmware
> > has them "backwards":
> > 
> >                     Device (COMB)
> >                     {
> >                         Name (_HID, EisaId ("PNP0501"))
> >                         Name (_DDN, "COM2")
> >                         Name (_UID, 0x02)
> > 
> >                     Device (COMA)
> >                     {
> >                         Name (_HID, EisaId ("PNP0501"))
> >                         Name (_DDN, "COM1")
> >                         Name (_UID, 0x01)
> 
> 
>   Yes, that's what I thought was weird in the DSDT, but thought the PnP layer
> would map those devices according to UID or at least DDN. It seems that's
> not the case.
> 
> > 
> > There's nothing illegal about this, but with the current PNPACPI,
> > it causes the names to be reversed.  The blind probe tries 0x3f8
> > first, and names that ttyS0.  But the PNP probe, using the namespace
> > order, finds the "COM2" port at 0x2f8 first:
> > 
> >   00:0b: ttyS0 at I/O 0x2f8 (irq = 3) is a 16550A
> >   00:0c: ttyS1 at I/O 0x3f8 (irq = 4) is a 16550A
> 
>   Oh I see, didn't notice this though.
> 
> > 
> > So I think your serial console would work without "legacy_serial.force"
> > if you used "console=ttyS1" instead of "console=ttyS0".  But you
> > shouldn't have to do that, of course.
> 
>   Will try ttyS1 just to confirm...
> 
>   Waiting for reboot...
> 
>   OK boots fine with the serial console fully operational again.

  But I also need to change my inittab. At least it confirms the
root cause of the problem.

  Sébastien.
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