linux-kernel - Re: 2.6.24: Serial disabled in BIOS but serial modules still loaded (probably PnP related)

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Date:	Sun, 25 Nov 2007 19:50:05 +0300
From:	Andrey Borzenkov <arvidjaar@...l.ru>
To:	"Yinghai Lu" <yhlu.kernel@...il.com>
Cc:	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-acpi@...r.kernel.org
Subject: Re: 2.6.24: Serial disabled in BIOS but serial modules still loaded (probably PnP related)

On Sunday 25 November 2007, Yinghai Lu wrote:
> On Nov 24, 2007 12:36 PM, Andrey Borzenkov <arvidjaar@...l.ru> wrote:
> > I have no COM port on notebook (without port replicator which I do not have)
> > so COM is disabled in BIOS. No ttyS* is detected during boot (and no device
> > created) but I just noticed that serial modules are still loaded. Well, this
> > partially defeats the purpose of disabling COM port - the intention was to
> > free resources by *not* loading unneeded modules ...
> >
> > This may have something to do with (ACPI) PnP which apparently believes COM is alive.
> > Notebook is Toshiba Portege 4000.
> >
> > {pts/0}% lsmod | grep 82
> > 8250_pnp                9792  0
> > 8250                   24660  1 8250_pnp
> > serial_core            22872  1 8250
> >
> > {pts/0}% lspnp -v
> > 00:00 PNP0c01 System board
> >     state = active
> >         mem 0x0-0x9ffff
> >         mem 0xe0000-0xeffff
> >         mem 0xf0000-0xfffff
> >         mem 0x100000-0x1ef5ffff
> >
> > 00:01 PNP0a03 PCI bus
> >     state = active
> >         io 0xcf8-0xcff
> >
> > 00:02 PNP0200 AT DMA controller
> >     state = active
> >         io 0x0-0xf
> >         io 0x81-0x83
> >         io 0x87-0x87
> >         io 0x89-0x8b
> >         io 0x8f-0x8f
> >         io 0xc0-0xdf
> >         dma 4
> >
> > 00:03 PNP0800 AT speaker
> >     state = active
> >         io 0x61-0x61
> >
> > 00:04 PNP0c04 Math coprocessor
> >     state = active
> >         io 0xf0-0xff
> >         irq 13
> >
> > 00:05 PNP0303 IBM enhanced keyboard (101/102-key, PS/2 mouse support)
> >     state = active
> >         io 0x60-0x60
> >         io 0x64-0x64
> >         irq 1
> >
> > 00:06 PNP0f13 PS/2 port for PS/2-style mice
> >     state = active
> >         irq 12
> >
> > 00:07 PNP0b00 AT real-time clock
> >     state = active
> >         io 0x70-0x71
> >         irq 8
> >
> > 00:08 PNP0c02 Motherboard resources
> >     state = active
> >         io 0x2e-0x2f
> >         io 0x62-0x62
> >         io 0x66-0x66
> >         io 0x80-0x80
> >         io 0x84-0x86
> >         io 0x88-0x88
> >         io 0x8c-0x8e
> >         io 0x92-0x92
> >
> > 00:09 PNP0501 16550A-compatible serial port
> >     state = active
> >         io 0x3f8-0x3ff
> >         irq 5
> >
> > 00:0a SMCf010 SMC Fast Infrared Port
> >     state = disabled
> >
> > 00:0b PNP0401 ECP printer port
> >     state = disabled
> >
> > ..
> > [  126.035809] Serial: 8250/16550 driver $Revision: 1.90 $ 4 ports, IRQ sharing enabled
> ....
> > [  126.107096] serial 00:09: activated
> ....
> 
> Can you cat /sys/firmware/acpi/DSDT and use iasl to decode it?
> it seems that your BIOS has problem about com setup.
> 

DSDT attached.

To illustrate the problem. Here is what I get booting exactly the same kernel
with the only difference that COM is enabled in BIOS:

[  147.721790] Serial: 8250/16550 driver $Revision: 1.90 $ 4 ports, IRQ sharing enabled
[  147.722658] serial8250: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
[  147.813557] 00:09: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A

When COM is disabled I get

[  235.865683] Serial: 8250/16550 driver $Revision: 1.90 $ 4 ports, IRQ sharing enabled
[  236.221995] serial 00:09: activated

No ttyS0 - and it is correct.

I'd expect that either serial driver should not be loaded at all in this case.

View attachment "dsdt.dsl" of type "text/x-objcsrc" (180789 bytes)

Download attachment "signature.asc " of type "application/pgp-signature" (190 bytes)