linux-kernel - Re: [PATCH v2 09/10] PCI: Sort pci root bus resources list

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Date:	Mon, 25 Nov 2013 21:18:41 -0700
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Gu Zheng <guz.fnst@...fujitsu.com>,
	Guo Chao <yan@...ux.vnet.ibm.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 09/10] PCI: Sort pci root bus resources list

On Mon, Nov 25, 2013 at 6:28 PM, Yinghai Lu <yinghai@...nel.org> wrote:
> Some x86 systems expose above 4G 64bit mmio in _CRS as non-pref mmio range.
> [   49.415281] PCI host bridge to bus 0000:00
> [   49.419921] pci_bus 0000:00: root bus resource [bus 00-1e]
> [   49.426107] pci_bus 0000:00: root bus resource [io  0x0000-0x0cf7]
> [   49.433041] pci_bus 0000:00: root bus resource [io  0x1000-0x5fff]
> [   49.440010] pci_bus 0000:00: root bus resource [mem 0x000a0000-0x000bffff]
> [   49.447768] pci_bus 0000:00: root bus resource [mem 0xfed8c000-0xfedfffff]
> [   49.455532] pci_bus 0000:00: root bus resource [mem 0x90000000-0x9fffbfff]
> [   49.463259] pci_bus 0000:00: root bus resource [mem 0x380000000000-0x381fffffffff]
>
> During assign unassigned 64bit mmio resource, it will go through
> every non-pref mmio for root bus in pci_bus_alloc_resource().
> As the loop is with pci_bus_for_each_resource(), and could have chance
> to use under 4G mmio range instead of above 4G mmio range if the requested
> range is not big enough, even it could handle above 4G 64bit pref mmio.
>
> For root bus, we can order list from high to low in pci_add_resource_offset(),
> during creating root bus, it will still keep the same order in final bus
> resource list.
>         pci_acpi_scan_root
>                 ==> add_resources
>                         ==> pci_add_resource_offset: # Add to temp resources
>                 ==> pci_create_root_bus
>                         ==> pci_bus_add_resource # add to final bus resources.
>
> After that, we can make sure 64bit pref mmio for pci bridges will be allocated
> higest of mmio non-pref, and in this case it is above 4G instead of under 4G.

Sorry I'm so slow; I'd like to know what problem this solves, too.
I'm trying to help people at distros figure out whether they will need
to backport this change.

> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
> ---
>  drivers/pci/bus.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
> index f801f6a..adf17858 100644
> --- a/drivers/pci/bus.c
> +++ b/drivers/pci/bus.c
> @@ -21,7 +21,8 @@
>  void pci_add_resource_offset(struct list_head *resources, struct resource *res,
>                              resource_size_t offset)
>  {
> -       struct pci_host_bridge_window *window;
> +       struct pci_host_bridge_window *window, *tmp;
> +       struct list_head *n;
>
>         window = kzalloc(sizeof(struct pci_host_bridge_window), GFP_KERNEL);
>         if (!window) {
> @@ -31,7 +32,17 @@ void pci_add_resource_offset(struct list_head *resources, struct resource *res,
>
>         window->res = res;
>         window->offset = offset;
> -       list_add_tail(&window->list, resources);
> +
> +       /* sorted it according to res end */
> +       n = resources;
> +       list_for_each_entry(tmp, resources, list)
> +               if (window->res->end > tmp->res->end) {
> +                       n = &tmp->list;
> +                       break;
> +               }
> +
> +       /* Insert it just before n */
> +       list_add_tail(&window->list, n);
>  }
>  EXPORT_SYMBOL(pci_add_resource_offset);
>
> --
> 1.8.1.4
>
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