Re: read/write[bwl] endian conversion for big-endian PCI ?

[Paul Mundt <lethal@linux-sh.org>]

On Mon, Mar 09, 2009 at 06:33:48PM +0900, Takashi Yoshii wrote:
> Reading the source code drivers/nic/r8169.c, 
> what I can guess about the system it has been written for, are
> 
> 1. Data structures transfered by PCI DMA are little endian.
>  It users explicit conversion when accessing descriptors.
> 
> 2. Data read/written by PCI target transfer are big(=cpu) endian.
>  MMIO registers are accessed read/write[bwl] without conversion.
>  Or perhaps read/write[bwl]() do the conversion.
>  I'v found some of powerPC platforms have such code for PCI space.
> 
> Because PCI is defined only for little-endian, endian conversion which
> PCI bridge on big-endian hardware provides can vary.
> I know I can not help conversion tasks depend on each platforms.
> 
This is a pretty common problem, we just haven't run in to it much in the
past since almost no one uses any PCI-capable SH part in big-endian mode.

Take a look at the CONFIG_SWAP_IO_SPACE on mips, we should be able to do
something pretty similar without much hassle.