[U-Boot] [PATCH v3 02/10] armv7: add miscellaneous utility macros

[Eric Cooper]

On Sun, May 15, 2011 at 03:15:46PM -0700, Simon Glass wrote:
> I believe that this problem is getting worse - e.g. USB on Tegra2 writes
> various fields of about 20 registers to get things up and running. I find
> translating SOC datasheet register definitions into C code with shifts and
> masks to be slow and error-prone work. Also we do need to maintain this
> code, and it gets reused for new SOC variants, etc. So it is not as if it is
> written once and then buried and forgotten. There is also a tendency to use
> 'magic' constants rather than #define values or something with a sensible
> name, then hopefully add a half-hearted comment. This requires constant
> return looks at the datasheet to see what bits were chosen.

I have nothing against helper functions like this (although I think they
should be inline functions, not macros, to guard against bugs
due to side-effects in arguments).

But wouldn't it be even better to define the registers as C structures
containing bitfields, so the C compiler can do the error-prone
shifting and masking?  Well-commented structure definitions for these
registers also eliminate the need to refer back to the datasheet when
working on the code.

-- 
Eric Cooper             e c c @ c m u . e d u