linux-kernel - Re: [PATCH v2 35/37] PCI: Make /sys/bus/pci/rescan rescan root

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Date:	Mon, 12 Mar 2012 21:44:37 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Jesse Barnes <jbarnes@...tuousgeek.org>, x86 <x86@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 35/37] PCI: Make /sys/bus/pci/rescan rescan root

On Sat, Mar 10, 2012 at 12:00 AM, Yinghai Lu <yinghai@...nel.org> wrote:
> It will rediscover removed pci root buses.
>
> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
> ---
>  drivers/pci/pci-sysfs.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index 4d122cb..fc0a7de 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -284,6 +284,7 @@ msi_bus_store(struct device *dev, struct device_attribute *attr,
>
>  #ifdef CONFIG_HOTPLUG
>  static DEFINE_MUTEX(pci_remove_rescan_mutex);
> +void __weak arch_pci_root_rescan(void) { }
>  static ssize_t bus_rescan_store(struct bus_type *bus, const char *buf,
>                                size_t count)
>  {
> @@ -295,6 +296,7 @@ static ssize_t bus_rescan_store(struct bus_type *bus, const char *buf,
>
>        if (val) {
>                mutex_lock(&pci_remove_rescan_mutex);
> +               arch_pci_root_rescan();
>                while ((b = pci_find_next_bus(b)) != NULL)
>                        pci_rescan_bus(b);
>                mutex_unlock(&pci_remove_rescan_mutex);

This is gross.  We used to rescan every previously-discovered PCI root bus.

Now, we do the same, plus:
1) Scan the ACPI namespace for PCI host bridges, adding and scanning
any we haven't seen before, and
2) scan domain 0, buses 0 - pcibios_last_bus, looking for any we
haven't seen before.

These just don't fit with the previous functionality.  The scan should
be done on the *ACPI namespace*, which is where any new bridges would
live.  It shouldn't be done in the PCI namespace.  The new bridges
aren't part of PCI.
--
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