Andrew Morton wrote:
> Johannes Stezenbach <[email protected]> wrote:
> >
> > From: Patrick Boettcher <[email protected]>
> >
> > Add big-endian register definitions for running on a PowerPC.
> > (Thanks to Paavo Hartikainen for testing.)
> >
> > ...
> > + struct {
> > + u32 dma_address0 :30;
> > + u32 dma_0No_update : 1;
> > + u32 dma_0start : 1;
> > + } dma_0x0;
> >...
> > +
> > + struct {
> > + u32 dma_0start : 1;
> > + u32 dma_0No_update : 1;
> > + u32 dma_address0 :30;
> > + } dma_0x0;
>
> Oh dear. This is a good demonstration of the downside of trying to use
> compiler bitfields to represent hardware registers. I have vague memories
> of writing BFINS and BFEXT in 3c59x to stomp this problem.
>
> I don't think there's any guarantee that the code you have there will work
> on all architectures/compiler versions btw.
>
> Also... The code appears to be assuming that BE architectures will
> bit-reverse their bitfields. Is that right? I'd expect them to only
> byte-reverse them?
Probably the code should use __BIG_ENDIAN_BITFIELD /
__LITTLE_ENDIAN_BITFIELD instead of __BIG_ENDIAN / __LITTLE_ENDIAN?
Anyway, the comment from the CVS commit suggests that it was tested.
I completely agree that this code is ugly as hell.
It was the obvious, simple fix to make the driver work on
PowerPC (and a few users happy), though. Rewriting the
driver not to use bitfields seems to be quite a bit of work.
Blame me for not paying enough attention when the initial
flexcop driver was submitted ;-(
Johannes
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