Re: [PATCH v3 3/8] PCI: Restore resource alignment

[Bjorn Helgaas <helgaas@kernel.org>]

On Wed, Aug 07, 2024 at 11:17:12AM -0400, Stewart Hildebrand wrote:
> Devices with alignment specified will lose their alignment in cases when
> the bridge resources have been released, e.g. due to insufficient bridge
> window size. Restore the alignment.

I guess this fixes a problem when the user has specified
"pci=resource_alignment=..." and we've decided to release and
reallocate a bridge window?  Just looking for a bit more concrete
description of what this problem would look like to a user.

> Signed-off-by: Stewart Hildebrand <stewart.hildebrand@amd.com>
> ---
> v2->v3:
> * no change
> 
> v1->v2:
> * capitalize subject text
> ---
>  drivers/pci/setup-bus.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
> index 23082bc0ca37..ab7510ce6917 100644
> --- a/drivers/pci/setup-bus.c
> +++ b/drivers/pci/setup-bus.c
> @@ -1594,6 +1594,23 @@ static void __pci_bridge_assign_resources(const struct pci_dev *bridge,
>  	}
>  }
>  
> +static void restore_child_resource_alignment(struct pci_bus *bus)
> +{
> +	struct pci_dev *dev;
> +
> +	list_for_each_entry(dev, &bus->devices, bus_list) {
> +		struct pci_bus *b;
> +
> +		pci_reassigndev_resource_alignment(dev);
> +
> +		b = dev->subordinate;
> +		if (!b)
> +			continue;
> +
> +		restore_child_resource_alignment(b);
> +	}
> +}
> +
>  #define PCI_RES_TYPE_MASK \
>  	(IORESOURCE_IO | IORESOURCE_MEM | IORESOURCE_PREFETCH |\
>  	 IORESOURCE_MEM_64)
> @@ -1648,6 +1665,8 @@ static void pci_bridge_release_resources(struct pci_bus *bus,
>  		r->start = 0;
>  		r->flags = 0;
>  
> +		restore_child_resource_alignment(bus);
> +
>  		/* Avoiding touch the one without PREF */
>  		if (type & IORESOURCE_PREFETCH)
>  			type = IORESOURCE_PREFETCH;
> -- 
> 2.46.0
>