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

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Date:	Fri, 8 Feb 2013 14:33:17 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
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 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.

Thanks

Yinghai
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