Re: PCI reading without endian conversion

[Matt Sealey <matt@genesi-usa.com>]

On Fri, Feb 20, 2009 at 3:07 PM, Ira Snyder <iws@ovro.caltech.edu> wrote:
> On Fri, Feb 20, 2009 at 02:05:08PM -0600, Matt Sealey wrote:
>> On Fri, Feb 20, 2009 at 1:11 PM, Ira Snyder <iws@ovro.caltech.edu> wrote:
>> > On Fri, Feb 20, 2009 at 12:57:36PM -0600, Matt Sealey wrote:
>> >
>> > I'm pretty sure memcpy_fromio() and memcpy_toio() will get you what you
>> > want. They don't change byte ordering.
>>
>> Are they guaranteed to only do 32-bit, aligned accesses?
>>
>
> I don't think so. I certainly wouldn't count on anything better than a
> byte-by-byte memcpy.
>
>> I made some cheats on my CPLD to ignore byte enables and so on,
>> because it makes the design cleaner and easier to read (for students)
>> plus, saves a ton of logic cells. It's totally within the PCI
>> standard, but it means if you do a byte read memcpy() you get.. very
>> weird results (i.e. not great).
>>
>
> Right, I understand how that works :)
>
> Some usage of cscope shows that __raw_readl() might be what you want,
> as well as __raw_writel() for writing. I'm not sure it is universally
> available, but maybe they are.
>
> The comment on PowerPC says "Non ordered and non-swapping "raw"
> accessors". Looks about right. ARM's implementation uses them to
> implement ioread32() and friends by adding byteswapping.

Am I correct in saying that cpu_to_le32 and le32_to_cpu are the
functions/macros I need to use to do byte swapping to make everything
go little endian (and back again when I read them back in the kernel)?

Or is there some cleverer way already implemented in the kernel?

-- 
Matt Sealey <matt@genesi-usa.com>
Genesi, Manager, Developer Relations