Re: [PATCH v4 2/3] dtc: Support character literals in cell lists

[David Gibson <david-xT8FGy+AXnRB3Ne2BGzF6laj5H9X9Tb+@public.gmane.org>]

On Mon, Sep 19, 2011 at 07:54:09PM -0700, Anton Staaf wrote:
> On Mon, Sep 19, 2011 at 5:59 PM, David Gibson
> <david-xT8FGy+AXnRB3Ne2BGzF6laj5H9X9Tb+@public.gmane.org> wrote:
> > On Mon, Sep 19, 2011 at 09:45:34AM -0700, Anton Staaf wrote:
> >> On Sun, Sep 18, 2011 at 7:00 PM, David Gibson
> >> <david-xT8FGy+AXnRB3Ne2BGzF6laj5H9X9Tb+@public.gmane.org> wrote:
> >> > On Sat, Sep 17, 2011 at 11:49:21AM -0500, Jon Loeliger wrote:
> >> >> > On Fri, Sep 09, 2011 at 12:16:30PM -0700, Anton Staaf wrote:
> >> >> > > With this patch the following property assignment:
> >> >> > >
> >> >> > >     property = <0x12345678 'a' '\r' 100>;
> >> >> > >
> >> >> > > is equivalent to:
> >> >> > >
> >> >> > >     property = <0x12345678 0x00000061 0x0000000D 0x00000064>
> >> >> > >
> >> >> > > Signed-off-by: Anton Staaf <robotboy-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
> >> >> >
> >> >> > Acked-by: David Gibson <david-xT8FGy+AXnRB3Ne2BGzF6laj5H9X9Tb+@public.gmane.org>
> >> >>
> >> >> So, I *think* we want to wait until the question of size
> >> >> is resolved some more, right?  Or, take this in any event
> >> >> as "without a type indicator they are all 32-bit values"?
> >> >
> >> > No this patch is fine to take without changing the cell size
> >> > semantics.  It's just that it becomes a lot more useful when we do get
> >> > those.
> >>
> >> Yup, I'm working on a size patch by the way.  Any comments on my
> >> previous post about it would be helpful.  But in the mean time I'm
> >> going ahead with a solution where the current cell size is stored in
> >> the "struct data" type references are not allowed in cell lists of
> >> size other than 32 bits.
> >
> > Ah, sorry, I meant to give comments on that earlier but got
> > sidetracked.
> >
> > Storing the cell size in struct data doesn't really work - a single
> > property could be assembled from several cell lists of different
> > sizes.  By the time the reference substitution happens, they will have
> > been all merged into a single struct data.
> >
> > I think prohibiting cell references anywhere but 32-bit cell lists is
> > the right approach, but we need to work out a way to do the check
> > during the parse phase.
> 
> Yes absolutely.  My intent with storing the current cell size in the
> data struct was to use that to do the parse time rejection of
> references in all but 32-bit cell lists.  That is the current cell
> size would not be used past parsing, for exactly the reason you
> mention.  My thought was that every creation of a cell list would set
> the current cell size to 32 or the value defined by /size/ and the
> closing '>' would set it back to 0.  The empty_data initializer would
> set the current cell size to 0, even though it should never be used
> outside of the <...> context.  Then when a reference or literal are to
> be appended to the current data struct we can check for the value 32
> if it's a reference, and otherwise use the current cell size to
> validate (ensure it fits in the current cell size) and pad (add
> leading zero's) the literal.  Padding won't actually be required if
> the literal parsing routine always returns a 64-bit value.

Oh, I see.  I guess that would work, but it's a really nasty misuse of
a long-term data structure to store some short-term information.  No,
I'm pretty sure we can rearrange the grammer to handle this more
cleanly.

Maybe something like this:

cellarrayprefix = DT_SIZE DT_LITERAL '<'
                | cellarrayprefix cellval
		| cellarrayprefix DT_REF
		| cellarrayprefix DT_LABEL

The semantic type of cellarray prefix would need to contain both a
struct data and a int for the cell size, which is a bit fiddly, but
should be doable.  The DT_REF case can check the cell size part of $1
and error if it's no 32-bit.

-- 
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