Re: [PATCH] pci: Workaround Stratus broken PCIE hierarchy

[Matthew Wilcox <matthew@wil.cx>]

On Thu, Nov 10, 2011 at 09:00:13AM -0500, Prarit Bhargava wrote:
> Stratus systems have a hierarchy that includes a PCIE Downstream bridge
> connected to a PCIE Upstream bridge and a PCI Downstream bridge.  The system
> boots with this wrong hierarchy into a crippled mode (USB doesn't work,
> network doesn't work ...).  Avoiding the Downstream bridge check in
> only_one_child() causes all the bridges to be enumerated and the system
> to function properly.

> @@ -1275,7 +1276,15 @@ static int only_one_child(struct pci_bus *bus)
>  	struct pci_dev *parent = bus->self;
>  	if (!parent || !pci_is_pcie(parent))
>  		return 0;
> -	if (parent->pcie_type == PCI_EXP_TYPE_ROOT_PORT ||
> +	if (parent->pcie_type == PCI_EXP_TYPE_ROOT_PORT)
> +		return 1;
> +	/*
> +	 * Stratus/NEC ftServer systems have a broken PCIE hierarchy in which
> +	 * one upstream and one downstream port are plugged into a downstream
> +	 * port.  Avoiding the downstream port check here results in a
> +	 * functional system.
> +	 */
> +	if (!dmi_name_in_vendors("ftServer") &&
>  	    parent->pcie_type == PCI_EXP_TYPE_DOWNSTREAM)
>  		return 1;
>  	return 0;

dmi_name_in_vendors is relatively expensive, so the order of these two
should be swapped, at least:

> 	if (parent->pcie_type == PCI_EXP_TYPE_DOWNSTREAM &&
>  	    !dmi_name_in_vendors("ftServer"))

Plus, this gets called for every PCI bridge.  We should be caching it
somewhere, so it's only called once.

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."