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

[Stewart Hildebrand <stewart.hildebrand@amd.com>]

On 8/8/24 15:28, Bjorn Helgaas wrote:
> 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.

Yes. When alignment has been specified via pcibios_default_alignment()
or by the user with "pci=resource_alignment=...", and the bridge window
is being reallocated, the specified alignment is lost and the resource
may not be sufficiently aligned after reallocation.

I can expand the commit description.

> 
>> 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
>>