Message-ID: <334319B2EBE0B144BAE1402B79D82DC5CE13B082@srvpegasus>
Date:	Fri, 27 May 2011 08:48:24 +0200
From:	"Hornung, Michael" <mhornung@...t-ka.de>
To:	'Bjorn Helgaas' <bhelgaas@...gle.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: AW: Kernel > 2.6.30: PCI issue causes Kernel freeze at booting

Hi Bjorn,

>>> Hi Michael,
>>>
>>> Any update on this problem?  Did it make any difference to put the
>>> UART in the ACPI namespace?
>>
>> thank you very much for your support. Unfortunately I'm not able to get it to work. I changed
>> the BIOS and added PNP0500 device nodes for all 21 UARTS (all located in the FPGA, all connected
>> via LPC, all located at addresses between 0x1900 and 0x19a7h and all using IRQ3), but the kernel does not care about
>> that nodes. CONFIG_SERIAL_8250_PNP is set to "y" (see attached config.txt) but the kernel output does not show
>> up any differences (2.6.38.6.log).
>
> Hmm, let's see...  It's been a while since I really worked in this area.
>
> I think there are two problems here: 
>
> 1) Something must be wrong with your PNP0500 devices because we only
> found seven PNP/ACPI devices, the same as we found in the original
> boot.Your most recent boot didn't have "debug" on the command line;
> that should show us the PNP devices we did find.  Can you post the
> DSDT?  Maybe it will have a clue about why we didn't find 28 (the
> original 7 + the new 21 UARTs) devices.

The BIOS sources were a little bit confusing at that point, but finally
I am able to add PNP device nodes.

> 2) Even if the PNP0500 devices were all there, Linux has a
> long-standing problem that we don't actually *do* anything with PNP
> resources until a driver claims the device.  This PCI assignment is
> happening before the serial driver would claim the devices, so I'm
> afraid it won't help with the problem you're seeing.  Ugh.  I've been
> wanting to fix this for years, but haven't had a chance to dig into
> it.

> It does seem unnecessary to assign I/O resources to the 00:1c.1 bridge
> at all, since there's no device below the bridge that needs I/O
> resources.  But changing that is a bigger project, too.

> There *is* an exception to the "Linux ignores PNP resources" rule,
> though -- maybe we could take advantage of that.  We do reserve
> "motherboard" resources (PNP0C01 and PNP0C02 devices), and there's
> even a comment in drivers/pnp/system.c about doing it early, before
> PCI assigns resources.  So if you change your new PNP0500 devices to
> PNP0C02 (and fix whatever is preventing PNPACPI from finding them),
> that might fix the PCI bridge assignment.  Then you'd have to keep the
> serial.h hack, since the serial driver wouldn't be able to claim the
> UARTs.

Thank you so much, that actually did the trick. I got it done to add a 
PNP0C02 device with a memory region from 0x1900 to 0x1947 and that is 
sufficient to get the kernel booting. 

> Ugh.  I'm really sorry you're tripping over this ugliness in Linux.

Don't mind, 21 UARTs, all starting at address 0x1900 is a little bit "special".

> The way this is *supposed* to work is that first, ACPI tells us where
> all the fixed hardware is.  The UARTs and PCI host bridges are
> examples of this fixed hardware.  Then we're supposed to enumerate
> things below the host bridges and assign unused space when necessary.
> But Linux has always discovered PCI stuff first, mostly ignoring ACPI,
> so keep tripping over problems like this.

> Bjorn


Again Bjorn, thank you very very much!

With best regards

Michael Hornung


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