Hi,
On Tue, 28 Jun 2005, Johannes Stezenbach wrote:
+ 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.
According to the user, it is tested and it is running flawlessly for
2 weeks now.
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 ;-(
It's my fault. The driver (skystar2) which has been replaced by the
flexcop-driver was so complicated to read, because of an IMHO abuse of
bitmask and bit-shifting. I absolutely wanted to bring more readability to
that driver without having the endian-issue in mind (rewrite was possible
after the vendor released the data sheets). Sorry for that.
regards,
Patrick.
--
Mail: [email protected]
WWW: http://www.wi-bw.tfh-wildau.de/~pboettch/
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