On Wednesday 24 October 2007, Alan Cox wrote:
> On Wed, 24 Oct 2007 18:20:52 -0700
> David Brownell <[email protected]> wrote:
>
> > Add a new resource_len() function, so drivers can start using this
> > instead of driver-private code for a common idiom. The call can be
> > useful with at least:
> >
> > - request_region(), release_region()
> > - request_mem_region(), release_mem_region()
> > - ioremap()
> >
> > Candidate drivers include those using platform or PNP busses, and
> > maybe some others. PCI already has a similar function.
> >
> > This patch also updates a representative set of drivers in two
> > subsystems to use this call (SPI, and USB peripheral/gadget).
>
> PCI also increasingly is using functions that allow the user to choose to
> map a resource as a resource (eg pci_iomap). So is it better to have
> functions request_mem_resource(res) free_mem_resource(res) and similar
> instead or as well ?
This was intended to be a minor band-aid. ;)
We already have request_resource(), which does something
different than the request_*region() calls. I think calls
with those names would complicate an already-too-strange
interface, adding oddball siblings to request_resource().
I'd hope that when those resource calls were defined they
made sense ... but to me, they don't do so today. Consider
that the *typical* caller is given a "struct resource", and
then to claim the specified address space it must convert
it into a "start + length" representation before getting
back a *NEW* "struct resource" ... with identical contents,
other than the value of one all-but-undocumented flag bit.
Then, if it's I/O space the address is usable already; but
for memory space, it still needs an ioremap()...
Oh, and PCI has its own resource structs ("BAR") that don't
look or act the same as other resources.
So while I like the notion of starting to abolish that
conversion step, this wasn't an attempt to fix all the
bizarre behaviors of the resource API.
I could imagine a call taking a resource and returning
a "void __iomem *" to use for IO, which implicitly claims
the region (in either memory or i/o space) and does any
ioremap needed for memory space. With a sibling call to
undo all that. If that's the answer, someone else should
develop the patch and update drivers...
- Dave
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