linux-kernel - Re: [RFC PATCH 01/16] PCI: Enhance pci_scan_root_bus() to support default IO/MEM resources

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Message-ID: <2447172.ADYWdCTnMP@wuerfel>
Date:	Tue, 18 Nov 2014 10:36:34 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Yijing Wang <wangyijing@...wei.com>,
	Liviu Dudau <liviu@...au.co.uk>,
	Tony Luck <tony.luck@...el.com>,
	Russell King <linux@....linux.org.uk>,
	linux-pci@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org, Xinwei Hu <huxinwei@...wei.com>,
	Thierry Reding <thierry.reding@...il.com>,
	Suravee.Suthikulpanit@....com,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	linux-ia64@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Wuyun <wuyun.wu@...wei.com>, linuxppc-dev@...ts.ozlabs.org,
	Yijing Wang <wangyijing0307@...il.com>
Subject: Re: [RFC PATCH 01/16] PCI: Enhance pci_scan_root_bus() to support default IO/MEM resources

On Tuesday 18 November 2014 15:44:23 Yijing Wang wrote:
> On 2014/11/17 18:08, Arnd Bergmann wrote:
> > On Monday 17 November 2014 18:21:35 Yijing Wang wrote:
> >> -       list_for_each_entry(window, resources, list)
> >> -               if (window->res->flags & IORESOURCE_BUS) {
> >> -                       found = true;
> >> -                       break;
> >> -               }
> >> +       if (!resources) {
> >> +               pci_add_resource(&default_res, &ioport_resource);
> >> +               pci_add_resource(&default_res, &iomem_resource);
> >> +               pci_add_resource(&default_res, &busn_resource);
> >> +       } else {
> >>
> > 
> > Isn't it almost always wrong to do this? You are adding all of the
> > I/O ports and memory to the host bridge, which will prevent you from
> > adding another host bridge, and the iomem_resource normally
> > includes a lot of addresses that are not accessible by the PCI host.
> 
> Hi Arnd, pci host bridge windows are the ranges allow child devices to setup
> from. Add all of IO/MEM here just a limit to child devices, no request for these
> resources, so it won't hurt another host bridge. Some platforms have no dts or ACPI
> report host bridge resources, in this case, we directly assign ioport/iomem_resources
> as the root resources of PCI devices.

But it would be wrong to allow hosts to allocate a device BAR that is not
visible through the host bridge. I think we need to keep these separate
from the general case: if you call any of the modern interfaces you have
to provide the resources and a device. I notice that there is only one
caller of pci_scan_bus_parented(), we should probably change that over to
pci_scan_root_bus() or your new interface and remove the old one, but
keep pci_scan_bus() as the only entry point for all of the legacy users
that do not know about the resources.

	Arnd
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