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: <20141118142354.GH12037@e106497-lin.cambridge.arm.com>
Date:	Tue, 18 Nov 2014 14:23:54 +0000
From:	Liviu Dudau <Liviu.Dudau@....com>
To:	Yijing Wang <wangyijing@...wei.com>
Cc:	Arnd Bergmann <arnd@...db.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Liviu Dudau <liviu@...au.co.uk>,
	Tony Luck <tony.luck@...el.com>,
	Russell King <linux@....linux.org.uk>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"huxinwei@...wei.com" <huxinwei@...wei.com>,
	Thierry Reding <thierry.reding@...il.com>,
	"suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Wuyun <wuyun.wu@...wei.com>,
	"linuxppc-dev@...ts.ozlabs.org" <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 Tue, Nov 18, 2014 at 11:46:06AM +0000, Yijing Wang wrote:
> On 2014/11/18 17:36, Arnd Bergmann wrote:
> > 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.
> 
> Ok, I will move this out of the generic interface.

My suggestion would actually be to trigger a warning/error if you detect that the resources
are missing. That way we can force the drivers to clean up.

Best regards,
Liviu

> 
> Thanks!
> Yijing.
> 
> > 
> > 	Arnd
> > 
> > .
> > 
> 
> 
> -- 
> Thanks!
> Yijing
> 
> --
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> 

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