Re: [PATCH v2 08/12] macintosh/via-pmu68k: Don't load driver on unsupported hardware

From: Finn Thain
Date: Sat Jun 09 2018 - 08:20:52 EST

> > > Is this enum used by any user space code? If so, perhaps rather
> > > leave the PMU_68K_V1 in there to avoid upsetting that?
> >
> > It also changes the value of PMU_68K_V2, which is an ABI break.
> Yes, that's what I worry about - but do we know of any users of that
> particular interface?

There is no ABI issue AFAIK. The value of pmu_kind is visible to userland
only on powerpc. /dev/pmu and /proc/pmu/* do not exist on m68k. This patch
series will make these UAPIs available on m68k, and for that reason I've
chosen the value PMU_UNKNOWN for pmu_kind.

New pmu_kind values can be defined as and when the need arises. But that
would imply a useful classification scheme for pre-PCI powerbooks, and I
don't know what that scheme will look like because at this stage there is
neither userland nor kernel code to support backlight, buttons and battery
for pre-PCI powerbooks.

In anycase, the "v1" and "v2" scheme is obviously inadequate when you
consider the range of m68k powerbook models. Also, consider the
out-of-tree adaptation of via-pmu by the Nubus-PMac project, which has
this ABI break:

diff --git a/include/linux/pmu.h b/include/linux/pmu.h
index cafe98d9694..9882a185a52 100644
--- a/include/linux/pmu.h
+++ b/include/linux/pmu.h
@@ -90,6 +90,7 @@ enum {
PMU_HEATHROW_BASED, /* PowerBook G3 series */
PMU_PADDINGTON_BASED, /* 1999 PowerBook G3 */
PMU_KEYLARGO_BASED, /* Core99 motherboard (PMU99) */
+ PMU_NUBUS_BASED, /* 1400, 2300, 5300 */
PMU_68K_V1, /* 68K PMU, version 1 */
PMU_68K_V2, /* 68K PMU, version 2 */

(BTW, these powerbooks are not "nubus based", they are "pre-PCI", so I
wouldn't want this to go upstream in this form. It could be that