[Skiboot] [PATCH v2 4/5] external/opal-prd: Support manufacturing command HTMGT and attribute override

[Jeremy Kerr]

Hi Patrick,

> I believe it was Ben and I that originally worked this out.  The
> thinking was that we only needed to change the version when an existing
> API changed and that we made the structure sufficiently big enough that
> any new function would just show up as a NULL to new firmware.

Without speaking for Ben here, I assume he'd have the intention that we
use up those function pointers.

> Changing the structure size is only a problem if we add 32 functions
> between two levels we need to support.  Otherwise, neither side goes
> outside the boundaries of the function.

It's a problem even with <32 functions if we ever do anything to the
struct as a whole (eg., rely on sizeof()).

For example, we need to keep our own copy of the function pointers,
byte-swapped:

	sz = sizeof(struct runtime_interfaces)/sizeof(uint64_t);
	s = (uint64_t *)hservice_runtime;
	d = (uint64_t *)&hservice_runtime_fixed;
	/* Byte swap the function pointers */
	for (i = 0; i < sz; i++)
		d[i] = be64toh(s[i]);

If our size doesn't match the size of the memory that exists in the
hostboot memory, then we'd potentially access invalid memory.

> At what point is opal-prd considered "released" such that it is in an
> official distribution and will require long-term support?  Are we
> already past that point?  I am fine with changing our direction at that
> point and starting to reduce the function pointer count as we add new
> interfaces.

We're at that point now; opal-prd is on its way into Ubuntu and RHEL.

Cheers,


Jeremy