Re: PCI reading without endian conversion

[Ira Snyder <iws@ovro.caltech.edu>]

On Fri, Feb 20, 2009 at 12:57:36PM -0600, Matt Sealey wrote:
> Hi guys,
> 
> What's the correct way to read from PCI address space (basically it's
> guaranteed to be non-coherent memory bar) without flipping bits like
> ioread32() does?
> 
> I need to be able to copy a bank of registers from PCI address space
> into a temporary buffer so I can compare them in userspace through
> UIO. Because of the flipping and the difference between the original
> kernel driver (which used ioread32() and therefore "saw" big endian)
> and the userspace app (which has a direct view of the PCI space, and
> therefore "sees" little endian) I decided to give userspace an
> absolutely consistent little-endian view seeing as this may get ported
> to ARM in the coming months.
> 
> I want to put as little code in there as possible and not laboriously
> manually flip from my ioread32() big endian values to little endian
> again (waste of time and code) if I can help it. Being able to read
> the raw value would help a lot, and if I need to do calculations on a
> small portion of the data then I can do the flips manually then (using
> le32_to_cpu and cpu_to_le32 which will be a noop on ARM), reducing the
> amount of porting I need to do in both kernel and userspace alike.
> 
> So, is there something like a direct ioread32le() or so, which will
> not change behaviour across architectures, is present on ARM and PPC,
> and will handle both PCI address space, and "normal" "ioremapped"
> memory?
> 

I'm pretty sure memcpy_fromio() and memcpy_toio() will get you what you
want. They don't change byte ordering.

Ira