Re: [PATCH 14/14] PCI/P2PDMA: Introduce pci_p2pdma_[un]map_resource()

Christoph Hellwig
2019-07-25T11:50:43Z

On Wed, Jul 24, 2019 at 10:06:22AM -0600, Logan Gunthorpe wrote:
> Yes. This is the downside of dealing only with a phys_addr_t: we have to
> look up against it. Unfortunately, I believe it's possible for different
> BARs on a device to be in different windows, so something like this is
> necessary unless we already know the BAR the phys_addr_t belongs to. It
> might probably be sped up a bit by storing the offsets of each bar
> instead of looping through all the bridge windows, but I don't think it
> will get you *that* much.
>
> As this is an example with no users, the answer here will really depend
> on what the use-case is doing. If they can lookup, ahead of time, the
> mapping type and offset then they don't have to do this work on the hot
> path and it means that pci_p2pdma_map_resource() is simply not a
> suitable API.

Ok. So lets just keep this out as an RFC and don't merge it until an
actual concrete user shows up.