Re: [PATCH v2] dtc: Add support for named integer constants

On Thu, Sep 08, 2011 at 06:18:21AM -0700, Simon Glass wrote:

Hi Stephen,

On Thu, Sep 8, 2011 at 6:09 AM, Simon Glass [off-list ref] wrote:

quoted

Hi Stephen,

On Fri, Sep 2, 2011 at 11:34 AM, Stephen Warren [off-list ref] wrote:

quoted

Stephen Warren wrote at Tuesday, August 30, 2011 3:30 PM:

quoted

You may define constants as follows:

/define/ TWO 2;
/define/ FOUR 4;
/define/ OTHER FOUR;

And properties may use these values as follows:

foo = <1 TWO 3 FOUR 5>;

Signed-off-by: Stephen Warren <redacted>

David, Jon,

Does this seem reasonable?

I think the syntax is simple enough it wouldn't interfere with any more
advanced expression/function/... support in the future, and it could be
easily extended to allow e.g.:

/define/ FOO "BAR";
/define/ BAX [0af8dacb0];
...

This seems very reasonable to me, and very useful. From the syntax it
looks like lower case symbols are allowed also, which is fine with me.

I hope that this can go into dtc as we would definitely use it.

Regards,
Simon

quoted

And even arbitrary expressions on the RHS as/when/if support is added
for those more generally:

/define/ A (B | (C << 2));

[in a separate email since I don't want to pollute my comments on
Stephen's nice patch with separate ravings]

Thinking of bitfields, we already have a problem with the way GPIOs
are specified. Typically we do something like:

something = <&gpio 46 5>

and define the third parameter to be three bits (direction, initial
value, polarity). It would be nice to be able to do something like:

something = <&gpio 46 INPUT,ACTIVE_LOW>
something-else = <&gpio 46 OUTPUT,HIGH>

instead. That would avoid having to explicitly have expressions
containing | or define all combinations like this:

I really don't like the idea of adding an extra explicit syntax for
bitfields.  I much prefer just implementing integer expressions, which
would allow the same thing through |.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson