linux-kernel - Re: [PATCH] Enable legacy support for serial ports when SERIAL_8250

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Date:	Mon, 9 Jul 2007 19:30:59 +0200
From:	Luca <kronos.it@...il.com>
To:	"Bjorn Helgaas" <bjorn.helgaas@...com>
Cc:	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Enable legacy support for serial ports when SERIAL_8250_PNP is disabled

On 7/9/07, Bjorn Helgaas <bjorn.helgaas@...com> wrote:
> On Saturday 07 July 2007 05:33:00 pm Luca Tettamanti wrote:
> > your patch:
> >
> > commit 7e92b4fc345f5b6f57585fbe5ffdb0f24d7c9b26
> > Author: Bjorn Helgaas <bjorn.helgaas@...com>
> > Date:   Tue May 8 00:36:07 2007 -0700
> >
> >     x86, serial: convert legacy COM ports to platform devices
> >
> > disables probing using legacy code in favour of ACPI/PNP to avoid double
> > discovery.
> >
> > However if SERIAL_8250_PNP is not enabled the user is left without
> > serial ports (been there, done that - my kernel config suddenly wasn't
> > working anymore). So:
>
> Yes, that's true.  Kconfig should automatically turn on SERIAL_8250_PNP
> if PNP and SERIAL_8250 are selected, but it does give you a choice if
> you have EMBEDDED set.  So I guess you must have this:
>
>   CONFIG_EMBEDDED=y
>   CONFIG_PNP=y
>   CONFIG_SERIAL_8250=y
>   CONFIG_SERIAL_8250_PNP=n
>
> Why do you want PNP support, but not 8250_PNP support?

That's a good question :-) IIRC the serial PNP code used to mess up
the mode of the port on my laptop, making it useless for debugging the
boot. Bug was fixed long ago, but I didn't re-enabled that option.

> If you turn off
> PNP completely, you will have "pnp_platform_devices == 0", and the
> existing code will do what you need.

Well for me it's a non-issue, I'm able to "work-around" it in many
ways. My point is that a configuration that used to work and is still
valid suddenly doesn't work anymore. I missed the dependacy on
CONFIG_EMBEDDED though, so feel free to ignore the patch ;-)

Luca
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