linux-kernel - Re: BAR 14: can't assign mem (size 0x200000)

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Message-ID: <CAOULuOaUke-W1W0o=1rhhk43Fy_RAYLdfhXQjdhy2xjHxP0oWA@mail.gmail.com>
Date:	Sat, 29 Mar 2014 20:14:30 -0400
From:	Parag Warudkar <parag.lkml@...il.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Yinghai Lu <yinghai@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>, linux-pci@...r.kernel.org,
	linux-acpi@...r.kernel.org
Subject: Re: BAR 14: can't assign mem (size 0x200000)

On Sat, Mar 29, 2014 at 1:19 PM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
> [+cc Rafael, linux-pci, linux-acpi]
>
> On Sat, Mar 29, 2014 at 09:41:20AM -0700, Linus Torvalds wrote:

>> Parag, can you add a WARN_ON_ONCE() to that message, so that we see
>> what the call chain is for it.
>
> I think we likely get a Bus Check notification when resuming, so we're
> probably in this path:
>
>     acpi_hotplug_notify_cb
>       acpi_hotplug_execute(acpi_device_hotplug, ...)
>         acpi_device_hotplug
>           acpi_scan_bus_check
>             acpi_pci_root_scan_dependent        # .hotplug.scan_dependent
>               acpiphp_check_host_bridge
>                 acpiphp_check_bridge
>                   enable_slot
>                     pcibios_resource_survey_bus
>                       dev_printk("Allocating resources")
>
> It seems like we ought to do the equivalent of a Bus Check from the
> root at boot-time, even if we don't receive an explicit Bus Check
> notification then (ACPI 5.0, sec 5.6.6, says "OSPM will typically
> perform a full enumeration automatically at boot time, but after
> system initialization it is the responsibility of the ACPI AML code to
> notify OSPM whenever a re-enumeration operation is required"), but I
> don't think we do, which makes the resume path different from the boot
> path.
>
> Parag, would you mind collecting an acpidump and attaching it to the
> bugzilla below?

I have attached a single acpidump to the bugzilla.

I realized that I misspoke when I said VTd makes a difference.
Actually on 3.14 exact same message appears on resume irrespective of
whether or not VTd is enabled.

However on 3.11 (3.11.0-18-generic Ubuntu LTS latest kernel) - I don't
see those messages irrespective of VTd status.
I must have accidentally booted into 3.11 kernel after disabling VTd
and thought the messages went away because of disabling VTd.

So we can ignore the VTd part.

>
> Is this a regression?  I guess you said that the message (and the sec-
> latency change, which I don't think is applicable to PCIe anyway) are
> the only ill effects you see, so it might not be too serious even if
> it is.

Not sure if Ubuntu includes any patches on top of 3.11 mainline that
make a difference to this issue - but in case they don't this might be
a regression.
About the seriousness part - I am not seeing any issues in my regular
use. Not sure what that bridge does and if there are any specific
devices involved - so it might just be that I am not using anything
that could be problematic due to this issue.

Thanks,

Parag
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