Subject: Re: [PATCH] powerpc/pci: save P2P bridge resource if possible

From: Benjamin Herrenschmidt <[email-masked]>
Date: Mon, 04 Jun 2012 18:55:22 +1000

On Mon, 2012-06-04 at 16:15 +0800, Gavin Shan wrote:
> When PCI probe flag PCI_REASSIGN_ALL_RSRC has been passed into PCI
> core, it's hoped that all resources to be reassigned by PCI core.
> As to particular P2P (PCI-to-PCI) bridge, the size of the corresponding
> BAR (I/O, MMIO, prefetchable MMIO) is calculated by the resources
> required by the PCI devices behind the P2P bridge. That means that
> the information like start/end address retrieved from the hardware
> registers of the P2P bridge is meainingless in the case. However,
> we still count that in and the BARs might have been configured by
> firmware with non-zero size. That leads to space waste.
> 
> The patch explicitly sets the size of P2P bridge BARs to zero in
> case that resource reassignment is expected with PCI probe flag
> PCI_REASSIGN_ALL_RSRC. In the result, it will save overall resource
> required by the system without waste.

Hrm... there was a reason I wasn't doing that .... but I can't
remember what it was, it's possible it no longer applies. I'll
have to make sure this patch is tested on various 4xx and FSL
configs.

Cheers,
Ben.

> Signed-off-by: Gavin Shan <[email-masked]>
> ---
>  arch/powerpc/kernel/pci-common.c |   16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/pci-common.c b/arch/powerpc/kernel/pci-common.c
> index 8e78e93..0fe214d 100644
> --- a/arch/powerpc/kernel/pci-common.c
> +++ b/arch/powerpc/kernel/pci-common.c
> @@ -966,13 +966,14 @@ static void __devinit pcibios_fixup_bridge(struct pci_bus *bus)
>  		if (i >= 3 && bus->self->transparent)
>  			continue;
>  
> -		/* If we are going to re-assign everything, mark the resource
> -		 * as unset and move it down to 0
> +		/* If we're going to reassign everything, we can
> +		 * shrink the P2P resource to have size as being
> +		 * of 0 in order to save space.
>  		 */
>  		if (pci_has_flag(PCI_REASSIGN_ALL_RSRC)) {
>  			res->flags |= IORESOURCE_UNSET;
> -			res->end -= res->start;
>  			res->start = 0;
> +			res->end = -1;
>  			continue;
>  		}
>  
> @@ -1234,7 +1235,14 @@ void pcibios_allocate_bus_resources(struct pci_bus *bus)
>  		pr_warning("PCI: Cannot allocate resource region "
>  			   "%d of PCI bridge %d, will remap\n", i, bus->number);
>  	clear_resource:
> -		res->start = res->end = 0;
> +		/* The resource might be figured out when doing
> +		 * reassignment based on the resources required
> +		 * by the downstream PCI devices. Here we set
> +		 * the size of the resource to be 0 in order to
> +		 * save more space.
> +		 */
> +		res->start = 0;
> +		res->end = -1;
>  		res->flags = 0;
>  	}
>