From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Finn Thain <fthain@telegraphics.com.au>
Cc: Michael Schmitz <schmitzmic@gmail.com>,
Andreas Schwab <schwab@linux-m68k.org>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
linux-m68k <linux-m68k@lists.linux-m68k.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 08/12] macintosh/via-pmu68k: Don't load driver on unsupported hardware
Date: Sun, 10 Jun 2018 10:29:45 +0200 [thread overview]
Message-ID: <CAMuHMdUHnFKzhe3x3=bG63HwnM7psu7AA=nba8q+nTDnxBAryw@mail.gmail.com> (raw)
In-Reply-To: <alpine.LNX.2.21.1806092140410.26@nippy.intranet>
Hi Finn,
On Sat, Jun 9, 2018 at 2:20 PM Finn Thain <fthain@telegraphics.com.au> 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@linux-m68k.org
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
next prev parent reply other threads:[~2018-06-10 8:30 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-08 2:24 [PATCH v2 00/12] macintosh: Resolve various PMU driver problems Finn Thain
2018-06-08 2:24 ` [PATCH v2 02/12] macintosh/via-pmu: Add missing mmio accessors Finn Thain
2018-06-08 2:24 ` [PATCH v2 01/12] macintosh/via-pmu: Fix section mismatch warning Finn Thain
2018-06-08 2:24 ` [PATCH v2 03/12] macintosh/via-pmu: Don't clear shift register interrupt flag twice Finn Thain
2018-06-08 2:24 ` [PATCH v2 07/12] macintosh/via-pmu: Make CONFIG_PPC_PMAC Kconfig deps explicit Finn Thain
2018-06-08 2:24 ` [PATCH v2 10/12] macintosh: Use common code to access RTC Finn Thain
2018-06-08 2:24 ` [PATCH v2 08/12] macintosh/via-pmu68k: Don't load driver on unsupported hardware Finn Thain
2018-06-09 6:42 ` Michael Schmitz
2018-06-09 7:14 ` Andreas Schwab
2018-06-09 7:55 ` Michael Schmitz
2018-06-09 12:21 ` Finn Thain
2018-06-09 13:24 ` Andreas Schwab
2018-06-10 2:11 ` Finn Thain
2018-06-10 6:55 ` Benjamin Herrenschmidt
2018-06-11 23:47 ` Finn Thain
2018-06-12 6:53 ` Laurent Vivier
2018-06-12 20:12 ` Michael Schmitz
2018-06-10 8:29 ` Geert Uytterhoeven [this message]
2018-06-10 9:12 ` Michael Schmitz
2018-06-11 0:05 ` Benjamin Herrenschmidt
2018-06-11 1:45 ` Michael Schmitz
2018-06-08 2:24 ` [PATCH v2 05/12] macintosh/via-pmu: Replace via pointer with via1 and via2 pointers Finn Thain
2018-06-08 2:24 ` [PATCH v2 09/12] macintosh/via-pmu: Replace via-pmu68k driver with via-pmu driver Finn Thain
2018-06-08 2:24 ` [PATCH v2 06/12] macintosh/via-pmu: Add support for m68k PowerBooks Finn Thain
2018-06-08 2:24 ` [PATCH v2 12/12] macintosh/via-pmu: Disambiguate interrupt statistics Finn Thain
2018-06-08 2:24 ` [PATCH v2 11/12] macintosh/via-pmu: Clean up " Finn Thain
2018-06-08 2:24 ` [PATCH v2 04/12] macintosh/via-pmu: Enhance state machine with new 'uninitialized' state Finn Thain
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