Re: [PATCH] imsttfb 2.5.x

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

> Does readl handle byte swapping on the PPC. The registers expect the data 
> feed to them to be little endian. Actually this driver will only work on 
> the PPC and ix86 platform. Other big endian platforms are out of luck. 

Yes, readl/writel will do the right thing. Use of in_le32 here is
probably for pre-historical reasons ;)

All PCI capabale big endian platforms shall have proper byteswapping
readl/writel.

> P.S
>    This whole issue really sucks. I really wish there was a clean standard 
> api to this. 

There is one, and it's readl/writel ;)

The only real problem is that currently, we lack equivalent of the "s"
versions of in/out macros for mmio. This is a bit annoying for the few
rare case where they would be useful as those shouldn't byteswap, but
re-implementing with __raw_read/writel (which doesn't byteswap neither)
is nasty because it exposes the barrier problem to the driver.

It would be convenient to define {read,write}s{b,w,l} so the IO
accessors and MMIO accessors apre perfectly symetric, but that's an
old debate...
 
Ben.



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