On 13 March 2012 12:36, Christoffer Dall <c.dall at virtualopensystems.com> wrote:
> + ? ? ? /*
> + ? ? ? ?* The CP15 c15 register is architecturally implementation
> + ? ? ? ?* defined, but some guest kernels attempt to read/write a
> + ? ? ? ?* diagnostics register here. We always return 0 and ignore
> + ? ? ? ?* writes and hope for the best.
> + ? ? ? ?*/
> + ? ? ? { CRn(15), CRm(DF), Op1(DF), Op2(DF), is32, ?WRITE, ignore_write, 1},
> + ? ? ? { CRn(15), CRm(DF), Op1(DF), Op2(DF), is32, ?READ, ?read_zero, ? ?1},
> +};
Incidentally, based on bitter experience with QEMU's cp15 emulation,
I predict that if you have this kind of wide-set default with no
documentation of exactly which cores need it you'll regret it in
the future, because you'll end up with a big mess and no idea of
whether something is wildcarded because of real guests that require
it or just because somebody was being lazy or because of a mis-read
TRM or what. I'd encourage you to aim for a model of locking it down
to "only exactly these registers on exactly this guest core", with
any deviations from the TRM-documented cp15 registers clearly commented
as to why they need to be present.
In particular, if we want to support both A9 and A15 guest cores we
should be doing it explicitly with different sets of cp15 registers
in each case, rather than defining some vague superset that kinda
sorta works for the guest kernels we happened to test.
-- PMM
