linux-kernel - Re: [PATCH v2 25/26] PCI: Disable mem in the ioapic removing path

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Date:	Fri, 8 Feb 2013 16:18:35 -0700
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 25/26] PCI: Disable mem in the ioapic removing path

On Fri, Feb 8, 2013 at 3:33 PM, Yinghai Lu <yinghai@...nel.org> wrote:
> On Fri, Feb 8, 2013 at 1:14 PM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
>> On Fri, Feb 8, 2013 at 12:28 PM, Yinghai Lu <yinghai@...nel.org> wrote:
>>> For physical hot plug should be ok, but for remove/rescan path will
>>> need us to disable that.
>>>
>>> otherwise rescan mmio resource for pci ioapic device will not be
>>> sized and allocated, aka skiped.
>>
>> When we scan other PCI devices, we can size memory BARs even if
>> PCI_COMMAND_MEMORY is already set.  So there must be something
>> different about IOAPICs?  Or maybe it's something different about
>> rescan vs. the initial scan?
>
> it is in drivers/pci/setup-bus.c::__dev_sort_resources()
> it will skip the reallocation for ioapic controller.
>
> ...
>         /* Don't touch ioapic devices already enabled by firmware */
>         if (class == PCI_CLASS_SYSTEM_PIC) {
>                 u16 command;
>                 pci_read_config_word(dev, PCI_COMMAND, &command);
>                 if (command & (PCI_COMMAND_IO | PCI_COMMAND_MEMORY))
>                         return;
>         }
>
>>
>>> For ioapic_probe:pci_enable_device will not enable the device
>>> correctly, and will bail out early.
>>
>> Exactly where and why do we bail out early?  The only early bail out I
>> see is where __pci_enable_device_flags() returns if "dev->enable_cnt >
>> 1".  Is that what you mean?
>
> pci_enable_device==>pci_enable_device_flags
> ==>do_pci_enable_device==>pcibios_enable_device==>pci_enable_resources
> ...
>                 if (!r->parent) {
>                         dev_err(&dev->dev, "device not available "
>                                 "(can't reserve %pR)\n", r);
>                         return -EINVAL;
>                 }
> ...
>
> only reassign one will have get it's parent.

Hmmm, OK.  So basically this patch is a hack to work around previous
hacks elsewhere.

We are like flies in a spider's web, bound tighter and tighter by
every loop of silk.
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