linux-kernel - Re: [PATCH 0/4] ACPI: kill acpi_pci_root

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Date:	Thu, 04 Oct 2012 21:54:36 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	Yinghai Lu <yinghai@...nel.org>, Len Brown <lenb@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-acpi@...r.kernel.org
Subject: Re: [PATCH 0/4] ACPI: kill acpi_pci_root_start

On Thursday 04 of October 2012 13:44:42 Bjorn Helgaas wrote:
> On Thu, Oct 4, 2012 at 12:36 PM, Yinghai Lu <yinghai@...nel.org> wrote:
> > On Thu, Oct 4, 2012 at 10:47 AM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
> >> On Wed, Oct 03, 2012 at 04:00:10PM -0700, Yinghai Lu wrote:
> >> This is a fundamental difference: at boot-time, all the ACPI devices below the
> >> host bridge already exist before the pci_root.c driver claims the bridge,
> >> while at hot-add time, pci_root.c claims the bridge *before* those ACPI
> >> devices exist.
> >>
> >> I think this is wrong.  The hot-plug case (where the driver is already
> >> loaded and binds to the device as soon as it's discovered, before the
> >> ACPI hierarchy below it is enumerated) seems like the obviously correct
> >> order.  I think we should change the boot-time order to match that, i.e.,
> >> we should register pci_root.c *before* enumerating ACPI devices.
> >
> > in booting path, all device get probed at first, and then register driver...
> > do you want to register all pci driver before probing pci devices?
> 
> I don't think we should have dependencies either way.  It shouldn't
> matter whether we enumerate devices first or we register the driver
> first.  That's why I think the current PCI/ACPI binding is broken --
> it assumes that we fully enumerate ACPI before the driver is
> registered.
> 
> To answer your specific question, yes, I do think drivers that are
> statically built in probably should be registered before devices are
> enumerated.  That way, the boot-time case is more similar to the
> hot-add case.
> 
> Obviously, for drivers that can be modules, the reverse must work as
> well (enumerate devices, then load and register the driver).  And then
> the other order (register driver, then enumerate device) must also
> work so future hot-adds of the same device type work.

Agreed.

Thanks,
Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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