linux-kernel - Re: [PATCH 1/2] PCI: leave MEM and IO decoding disabled during 64-bit BAR sizing, too

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Date:	Thu, 23 Aug 2012 11:20:12 -0700
From:	Olof Johansson <olof@...om.net>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	linux-pci@...r.kernel.org,
	Jacob Pan <jacob.jun.pan@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Ivan Kokshaysky <ink@...assic.park.msu.ru>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	Robert Hancock <hancockrwd@...il.com>,
	linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [PATCH 1/2] PCI: leave MEM and IO decoding disabled during 64-bit
 BAR sizing, too

Hi,

On Thu, Aug 23, 2012 at 11:02 AM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
> On Thu, Aug 23, 2012 at 12:28:23AM -0700, Olof Johansson wrote:
>> Hi,
>>
>> On Mon, Jul 9, 2012 at 11:20 AM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
>> > After 253d2e5498, we disable MEM and IO decoding for most devices while we
>> > size 32-bit BARs.  However, we restore the original COMMAND register before
>> > we size the upper 32 bits of 64-bit BARs, so we can still cause a conflict.
>> >
>> > This patch waits to restore the original COMMAND register until we're
>> > completely finished sizing the BAR.
>> >
>> > Reference: https://lkml.org/lkml/2007/8/25/154
>> > Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
>>
>> This patch causes boot lockup on PA Semi hardware, since it disables
>> the bar on the UART that is used for console, and it has printks
>> between the old and the new re-enable location. If I boot with 'debug'
>> level for printk, I hit this. If I boot with just regular console
>> args, I don't.
>>
>> I'm guessing any other platform that uses MMIO-based UART on PCI for
>> console will have similar issues. I can verify on Chrome OS x86
>> hardware tomorrow if legacy powerpc isn't important enough to care
>> about. :-)
>>
>> I have no proposal for a fix for this. Can you please consider
>> reverting for 3.6 unless someone has a better idea?
>
> Thanks a lot for finding and debugging this!
>
> Can you try the patch below?
>
>
> commit cfc29ece86d648e63fb46de81b2bf8e3e107672c
> Author: Bjorn Helgaas <bhelgaas@...gle.com>
> Date:   Thu Aug 23 10:53:08 2012 -0600
>
>     PCI: Don't print anything while decoding is disabled
>
>     If we try to print to the console device while its decoding is disabled,
>     the system will hang.
>
>     Reported-by: Olof Johansson <olof@...om.net>
>     Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>

Ah yes, of course. Teaches me to try to do anything productive late at
night. Tested fine here.

Acked-by: Olof Johansson <olof@...om.net>


Thanks!

-Olof
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