Re: [linux-usb-devel] Re: SLAB vs. pci_alloc_xxx in usb-uhci patch [RFC: API]

[David Brownell <david-b@pacbell.net>]

> >  > Do lots of drivers need the reverse mapping? It wasn't on my todo list
> >  > yet.
> > 
> > I am against any API which provides this.  It can be extremely
> > expensive to do this on some architectures, 

The implementation I posted needed no architecture-specific
knowledge.  If cost is the issue, fine -- this makes it finite,
(not infinite), and some drivers can eliminate that cost.


> >        and since the rest
> > of the PCI dma API does not provide such an interface neither
> > should the pool routines.
> 
> The API I hacked together for uhci.c didn't have this.

But it didn't handle the OHCI done-list processing, and we've heard
a lot more about pci_*_consistent being needed with OHCI than
with UHCI; it's more common on non-Intel architectures.

Given that some hardware must return the dma addresses, why
should it be a good thing to have an API that doesn't expose
the notion of a reverse mapping?  At this level -- not the lower
level code touching hardware PTEs.

- Dave