Hi Finn,
On Sat, Jun 9, 2018 at 2:20 PM Finn Thain <fthain@xxxxxxxxxxxxxxxxxxx> wrote:
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.
While /dev/pmu and /proc/pmu/* may not exist on m68k, definitions in
include/uapi/linux/pmu.h are part of the ABI, and cannot be changed or removed,
unless we are 100% sure there are no users.
If I would write a program interfacing with /dev/pmu and /proc/pmu/*, and
needing to check the PMU type, it would have a switch() statement with
all existing values defined in <linux/pmu.h>. So that would become broken
by your change.
Hence the enum is append-only.
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
New values can be added at the bottom.
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 */
};
That's bad. But as long as the NuBus-PMac project is out-of-tree, the
enum values it uses are not part of the Linux ABI, IMHO.
During upstreaming, PMU_NUBUS_BASED should be moved to the bottom.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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