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

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Message-ID: <BANLkTimX1KG-BZ98LH_NweOUOaUbQtZirg@mail.gmail.com>
Date:	Wed, 18 May 2011 07:56:04 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	"Hornung, Michael" <mhornung@...t-ka.de>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: Re: Kernel > 2.6.30: PCI issue causes Kernel freeze at booting

On Wed, May 18, 2011 at 1:44 AM, Hornung, Michael <mhornung@...t-ka.de> wrote:
>>> 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.

Makes sense; that's a common way for attaching UARTs, and they are
normally described via ACPI.  When you do that, I think it will show
up as ttyS4 (be sure you build with CONFIG_SERIAL_8250_PNP=y), so
you'll have to use "console=ttyS4" when you boot.  ttyS0-ttyS3 are
taken by the hard-coded ports in serial.h, even though they may not
exist on your platform.

Bjorn
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