[U-Boot] [PATCH 2/2 v12] Introduced btrfs file-system with btrload command

[Wolfgang Denk]

Dear Tom Rini,

In message <5186723E.2080503 at ti.com> you wrote:
>
> > These changes should be factored out into a separate commit. In any
> > case, the code should be compiled in only when needed, i. e. when
> > btrfs support is selected.  Otherwise you just bloat the code size
> > and build time for all systems without need.
> 
> We should be able to make lib/crc32_c.o depend on btrfs being set,
> yes.  But non-command stuff should be getting garbage collected out in
> most cases at last (Need to poke Albert about the patch for ARM).

Yes, it may be garbage collected, but only after compilation - which
means we add to the build time for about 1000 boards which do not use
this.

> > Hm... do we really need yet another crc32 implementation?
> 
> We talked about this before I believe and the answer is yes :(

Yes, I remember this discussion.  But look at the code.  It raises a
number of questions:

- Why do we have to calculate the crc32c_table[] at runtime?  Our
  regular CRC code uses a pre-calculated table; we should do the same
  here.

- Compare the code for crc32c_cal() in the patch with the definition
  of DO_CRC(x) in "lib/crc32.c" - to me, it appears to be the same for
  little endian code (it is redundant?), but different for big endian
  systems - which raises the question if this code has ever been
  tested on a BE machine?

- The code claims to be derived from "Linux kernel crypto/crc32c.c";
  but I cannot find such code in that file.

- The implementation of crc32c_cal() suffers from a few other problems
  (like not triggering the watchdog, which will cause problems on
  systems that use one).

I think we should re-check this.  My feeling is that we may eventually
end up with a different CRC table, but without need for new code.

Best regards,

Wolfgang Denk

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