linux-kernel - AW: Kernel > 2.6.30: PCI issue causes Kernel freeze at booting

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Date:	Wed, 18 May 2011 09:44:22 +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

Hello Bjorn,

>[added linux-pci]

>> On Tue, May 17, 2011 at 1:01 AM, Hornung, Michael <mhornung@...t-ka.de> wrote:
>> the system from which I'm talking about is a Menlow XL (Intel Atom Z510PT and SCH US15WPT) platform with 512 megabyte RAM.
>> There is one PCIe-switch (PI7C9X20404SL) attached to each of both PCIe-ports of the US15WPT (see attached 2.6.30-lspci.txt for details).

>I think you forgot to attach the lspci.

Sorry for that, I attached it to this mail.

>> With both switches enabled, all Kernel versions (vanilla) above 2.6.30 refuse to boot. With only one switch active
>> (the other one with no supply voltage ), all Kernel versions boot properly. It does not matter which switch is removed, it
>> is sufficient just to remove one of the two.
>>
>> There is an UART (FPGA IP Core) in that system located at address 1900h using interrupt 3. In order to get Kernel messages at boot time,
>> I changed file arch/x86/include/asm/serial.h as follows:
>>
>> -        { 0, BASE_BAUD, 0x3F8, 4, STD_COM_FLAGS },      /* ttyS0 */     \
>> +        { 0, BASE_BAUD, 0x1900, 3, STD_COM_FLAGS },     /* ttyS0 */    \
>>
>> that is the only change I made to the kernel sources.

> Is this UART connected via PCI?  I don't think so, because I don't see
> any I/O BARs that include 0x1900. 

The UART is connected via LPC bus.

> However, I don't see any ACPI
> devices that mention that address either (none of the "pnp 00:xx"
> devices include that range).

> Since there's no PCI-enumerable device that uses 0x1900, and ACPI
> doesn't mention it, we think it's available, and I notice the 2.6.38.6
> kernel does assign the [io  0x1000-0x1fff] range to the 00:1c.1 bridge
> I/O window.  Now we probably have two devices claiming accesses to
> 0x1900 (the bridge and the UART).  I don't know whether this is
> causing the problem, but it can't be good.

> I think the best way to fix this would be to change your BIOS to
> include a PNP0501 ACPI device with the appropriate _CRS to tell us
> what resources it uses (then you could drop your serial.h change,
> too).

I do have the BIOS sources so I'll try do to it that way, thank you very
much!

> If changing the BIOS is impossible, you could at least find out if
> this is the problem by adding a quirk in drivers/pnp/quirks.c to
> reserve the 0x1900 region by adding an I/O resource to the PNP0c02
> device.

> Bjorn


Thank you very much again for your help!

With best regards


Michael Hornung


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Michael Hornung
Hardware
Mobile Telematic and Fare Collection Systems

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