On Wednesday 08 August 2007 15:38:50 Andi Kleen wrote:
> On Wed, Aug 08, 2007 at 03:28:33PM +0200, Michael Buesch wrote:
> > On Wednesday 08 August 2007 15:08:28 Andi Kleen wrote:
> > > On Wed, Aug 08, 2007 at 03:02:35PM +0200, Michael Buesch wrote:
> > > > On Wednesday 08 August 2007 14:55:11 Andi Kleen wrote:
> > > > > On Wed, Aug 08, 2007 at 01:50:35PM +0200, Michael Buesch wrote:
> > > > > > On Wednesday 08 August 2007 14:38:10 Andi Kleen wrote:
> > > > > > > Jeff Garzik <[EMAIL PROTECTED]> writes:
> > > > > > > > > + val, reg_index, addr, addr+4); */
> > > > > > > > > + writel(cpu_to_le32(reg_index), addr);
> > > > > > > > > + writel(cpu_to_le32(val),(u8 *)addr + 4);
> > > > > > > >
> > > > > > > > wrong -- endian conversion macros not needed with writel()
> >
> > > > Fact is that we do _not_ need cpu_to_le32 with writel.
> > >
> > > We do on a big endian platform if the register is LE. I assume that's the
> > > case
> > > on this hardware.
> >
> > That is not true.
> > writeX does automatically convert to bus-endian.
> > Which, in case of the PCI bus, is little endian.
> > So if your register is LE (which it is most likely), you don't
> > need any conversion. If your register is BE (which I very much doubt),
> > then you need swab32().
> > In _no_ case you need cpu_to_xx().
>
> Hmm, I checked a couple of BE architectures and none seem to convert
> explicitely.
That depends on the arch.
Look at this from ppc, for example:
184 static inline void writel(__u32 b, volatile void __iomem *addr)
185 {
186 out_le32(addr, b);
187 }
out_le32 writes a little endian value. So it converts it.
Also note that b is __u32. Sparse would complain, if someone used cpu_to_xx
on it.
> But ok it's possible that their PCI bridges convert. I'll take your
> word for it although it sounds somewhat dubious.
>
> However if that's true then there are quite some drivers wrong:
>
> % grep -r write[bwl]\(cpu_to * | wc -l
> 57
Yeah, seems so.
Here comes an example (with 16bit values)
Little endian register
LittleEndian arch BigEngian arch
value 0xBBAA 0xAABB
writew 0xBBAA 0xAABB
on bus 0xBBAA 0xBBAA
on dev 0xBBAA 0xBBAA
Big endian register
LittleEndian arch BigEngian arch
value 0xBBAA 0xAABB
swab16 0xAABB 0xBBAA
writew 0xAABB 0xBBAA
on bus 0xAABB 0xAABB
on dev 0xAABB 0xAABB
I hope I got it right. :)
Same result on every arch.
Most hardware has little endian registers. Some can switch
endianess based on some bit, too. So in case of a BE register that
bit has to be flipped, or if not possible swabX() has to be used.
--
Greetings Michael.
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