Re: [RFC PATCH 0/3] generic hypercall support

Arnd Bergmann
2009-05-07T22:13:21Z

On Thursday 07 May 2009, Chris Wright wrote:
>
> > Chris, is that issue with the non ioread/iowrite access of a mangled
> > pointer still an issue here?  I would think so, but I am a bit fuzzy on
> > whether there is still an issue of non-wrapped MMIO ever occuring.
>
> Arnd was saying it's a bug for other reasons, so perhaps it would work
> out fine.

Well, maybe. I only said that __raw_writel and pointer dereference is
bad, but not writel.

IIRC when we had that discussion about io-workarounds on powerpc,
the outcome was that passing an IORESOURCE_MEM resource into pci_iomap
must still result in something that can be passed into writel in addition
to iowrite32, while an IORESOURCE_IO resource may or may not be valid for
writel and/or outl.

Unfortunately, this means that either readl/writel needs to be adapted
in some way (e.g. the address also ioremapped to the mangled pointer)
or the mechanism will be limited to I/O space accesses.

Maybe BenH remembers the details better than me.