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

From: Yijing Wang <[email-masked]>
Date: Tue, 18 Nov 2014 19:46:06 +0800

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.

Thanks!
Yijing.

> 	Arnd
> .

-- 
Thanks!
Yijing