Subject: Re: [PATCH 4/4] arm64: pci: acpi: Preserve PCI resources configuration when asked by ACPI

From: Bjorn Helgaas <[email-masked]>
Date: Fri, 21 Jun 2019 15:08:48 -0500

arm64: PCI: Preserve firmware configuration when necessary

On Sat, Jun 15, 2019 at 10:23:59AM +1000, Benjamin Herrenschmidt wrote:
> When _DSM #5 returns 0 for a host bridge, we need to claim the existing
> resources rather than reassign everything.

Use imperative mood.  I'd remove the reference to _DSM #5.  This patch
does not directly reference _DSM, and it's conceivable a kernel
command line parameter or other mechanism could set
host->preserve_config.

> Signed-off-by: Benjamin Herrenschmidt <[email-masked]>
> ---
>  arch/arm64/kernel/pci.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/arch/arm64/kernel/pci.c b/arch/arm64/kernel/pci.c
> index 1419b1b4e9b9..a2c608a3fc41 100644
> --- a/arch/arm64/kernel/pci.c
> +++ b/arch/arm64/kernel/pci.c
> @@ -168,6 +168,7 @@ struct pci_bus *pci_acpi_scan_root(struct acpi_pci_root *root)
>  	struct acpi_pci_generic_root_info *ri;
>  	struct pci_bus *bus, *child;
>  	struct acpi_pci_root_ops *root_ops;
> +	struct pci_host_bridge *hb;
>  
>  	ri = kzalloc(sizeof(*ri), GFP_KERNEL);
>  	if (!ri)
> @@ -193,6 +194,16 @@ struct pci_bus *pci_acpi_scan_root(struct acpi_pci_root *root)
>  	if (!bus)
>  		return NULL;
>  
> +	hb = pci_find_host_bridge(bus);
> +
> +	/* If ACPI tells us to preserve the resource configuration, claim now */
> +	if (hb->preserve_config)
> +		pci_bus_claim_resources(bus);
> +
> +	/*
> +	 * Assign whatever was left unassigned. If we didn't claim above, this will
> +	 * reassign everything.

Wrap the comment so it fits in 80 columns (unless local arch/arm64 style
allows wider lines, but I don't see any other wide lines in the file).

This series generally looks good to me.

> +	 */
>  	pci_assign_unassigned_root_bus_resources(bus);
>  
>  	list_for_each_entry(child, &bus->children, node)
> -- 
> 2.17.1
> 

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