linux-kernel - Re: How to access serial port that is set in BIOS as OS Controlled

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Message-ID: <Pine.LNX.4.64.1108121443200.26481@boston.corp.fedex.com>
Date:	Fri, 12 Aug 2011 15:01:11 +0800 (SGT)
From:	Jeff Chua <jeff.chua.linux@...il.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
cc:	Andrey Panin <pazke@...trinvest.ru>,
	lkml <linux-kernel@...r.kernel.org>,
	Matthew Garrett <mjg@...hat.com>
Subject: Re: How to access serial port that is set in BIOS as OS Controlled



On Fri, Aug 12, 2011 at 5:49 AM, Bjorn Helgaas <bhelgaas@...gle.com> 
wrote:

> Oops, my mistake.  You now need "pnp.debug=1" to turn the extra debug

Now, I do see more messages and "resources" show "active" ...


# dmesg
pnp 00:00: parse allocated resources
pnp 00:01: parse allocated resources
pnp 00:01: PNP0c02: calling 0xc11c8a0c
pnp 00:02: parse allocated resources
pnp 00:02: PNP0c02: calling 0xc11c8a0c
pnp 00:03: parse allocated resources
pnp 00:04: parse allocated resources
pnp 00:05: parse allocated resources
pnp 00:06: parse allocated resources
pnp 00:07: parse allocated resources
pnp 00:08: parse resource options
pnp 00:08:   dependent set 0 (acceptable) io  min 0x3f8 max 0x3f8 align 
1 size 8 flags 0x1
pnp 00:08:   dependent set 0 (acceptable) irq 4 flags 0x1
pnp 00:08: parse allocated resources
pnp 00:08: set resources
pnp 00:09: parse resource options
pnp 00:09:   dependent set 0 (acceptable) io  min 0x2f8 max 0x2f8 align 
1 size 8 flags 0x1
pnp 00:09:   dependent set 0 (acceptable) irq 3 flags 0x1
pnp 00:09: parse allocated resources
pnp 00:09: set resources
pnp 00:0a: parse resource options
pnp 00:0a:   dependent set 0 (acceptable) io  min 0x3e8 max 0x3e8 align 
pnp 00:0a:   dependent set 0 (acceptable) irq 6 flags 0x1
pnp 00:0a: pnp_assign_resources, try dependent set 0
pnp 00:0a: pnp_assign_resources succeeded: current resources:
pnp 00:0a: [io  0x03e8-0x03ef flags 0x40000101]
pnp 00:0a:   dependent set 0 (acceptable) irq 6 flags 0x1
pnp 00:0a: pnp_assign_resources, try dependent set 0
pnp 00:0a: pnp_assign_resources succeeded: current resources:
pnp 00:0a: [io  0x03e8-0x03ef flags 0x40000101]
pnp 00:0a: [irq 6 flags 0x40000401]
pnp 00:0a: set resources
pnp 00:0b: parse resource options
pnp 00:0b:   dependent set 0 (acceptable) io  min 0x2e8 max 0x2e8 align 
1 size 8 flags 0x1
pnp 00:0b:   dependent set 0 (acceptable) irq 12 flags 0x1
pnp 00:0b: parse allocated resources
pnp 00:0b: set resources
serial 00:0a: pnp_assign_resources, try dependent set 0
serial 00:0a: pnp_assign_resources succeeded: current resources:
serial 00:0a: [io  0x03e8-0x03ef flags 0x40000101]
serial 00:0a: [irq 6 flags 0x40000401]
serial 00:0a: pnp_start_dev: current resources:
serial 00:0a: [io  0x03e8-0x03ef flags 0x40000101]
serial 00:0a: [irq 6 flags 0x40000401]
serial 00:0a: set resources
serial 00:0a: encode 2 resources
serial 00:0a:   encode io 0x3e8-0x3ef decode 0x1
serial 00:0a:   encode irq 6 edge high exclusive (2-byte descriptor)


# cat /sys/bus/pnp/devices/00:0a/resources
state = active
io 0x3e8-0x3ef
irq 6


# setserial /dev/ttyS2
/dev/ttyS2, UART: 16550A, Port: 0x03e8, IRQ: 6


# echo activate > /sys/bus/pnp/devices/00:0a/resources
-bash: echo: write error: Device or resource busy

# dmesg
serial 00:0a: in use; can't configure
serial 00:0a: in use; can't configure


# echo disable > /sys/bus/pnp/devices/00:0a/resources
-bash: echo: write error: Device or resource busy

# dmesg
serial 00:0a: in use; can't configure
serial 00:0a: in use; can't configure


> This *should* work.  My guess is that it's failing because the I/O ports 
> at 0x3e8 are still reserved.  The PNP core doesn't actually reserve 
> anything, so it would have to be the 8250 driver.  It doesn't mention 
> those ports in dmesg, so maybe they get reserved when you do the 
> "setserial."

It's working better now. But, the port is now always active and can't be 
disabled.


> The 8250 driver has no idea that you disabled the PNP device, so it 
> would never release them.  Then when you try to activate it again, 
> they're still in use.  You can test this idea a little bit by looking at 
> /proc/ioports (1) immediately after boot, (2) before "setserial", (3) 
> after "setserial", and (4) after you disable the PNP device.

It always shows the same info, except I can't disable the port.

# cat /proc/ioports
   03e8-03ef : serial


Thanks,
Jeff
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