[U-Boot] [RESEND PATCH v2 1/5] Tegra2: Add macros to calculate bitfield shifts and masks

[Wolfgang Denk <wd@denx.de>]

Dear Anton Staaf,

In message <CAF6FioVs5rsF27Boq9+Bb+3Cgdh2m=jj1c=41a-32muBUd9wtw@mail.gmail.com> you wrote:
> 
> > Sorry, but because such code is unportable we do not accept it, as it
> > would lead to driver code that becomes unportable, too.
> >
> > I know that this is throwing more fuel on the fire (for which I am sorry),

You don't have to apologize.  I think it is important that everybody
understands the reasons behind such decisions.

> but I don't follow the argument that this is unportable.  As far as I can
> tell, the # : # syntax is not using any special compiler extensions, it is
> simply substituted into a (boo) ? # : # expression, thus extracting either
> the first of second number from the definition of the bit field.
> 
> If I am wrong I would be interested to know what about this is not standard
> pre-processor usage?

I did not say anything about preprocessor issues.  The use of bit
numbers (and ranges of bit numbers) in code is inherently unportable.

For example:

"Bit 10" means 0x00000400 on some systems (like, for example, on ARM),
but  it  means 0x00200000 on others (like, for example, on PPC).

On many systems bit 0 means trhe LSB, but the Power Architecture
defines it as the MSB.  Thus bit numbers should never be used in any
code to access bits or to create masks etc. - they are not generally
applicable.

Best regards,

Wolfgang Denk

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