linux-kernel - Re: [PATCH 08/11] macintosh/via-pmu: Replace via-pmu68k driver with via-pmu driver

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Date:   Wed, 6 Jun 2018 16:57:31 +1000 (AEST)
From:   Finn Thain <fthain@...egraphics.com.au>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Michael Schmitz <schmitzmic@...il.com>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 08/11] macintosh/via-pmu: Replace via-pmu68k driver with
 via-pmu driver

On Mon, 4 Jun 2018, Geert Uytterhoeven wrote:

> 
> > Don't call pmu_shutdown() or pmu_restart() on early PowerBooks: the 
> > PMU device found in these PowerBooks isn't supported.
> 
> Shouldn't that be a separate patch?
> 
> > --- a/arch/m68k/mac/misc.c
> > +++ b/arch/m68k/mac/misc.c
> 
> > @@ -477,9 +445,8 @@ void mac_poweroff(void)
> >                    macintosh_config->adb_type == MAC_ADB_CUDA) {
> >                 cuda_shutdown();
> >  #endif
> > -#ifdef CONFIG_ADB_PMU68K
> > -       } else if (macintosh_config->adb_type == MAC_ADB_PB1
> > -               || macintosh_config->adb_type == MAC_ADB_PB2) {
> > +#ifdef CONFIG_ADB_PMU
> > +       } else if (macintosh_config->adb_type == MAC_ADB_PB2) {
> >                 pmu_shutdown();
> >  #endif
> >         }
> > @@ -519,9 +486,8 @@ void mac_reset(void)
> >                    macintosh_config->adb_type == MAC_ADB_CUDA) {
> >                 cuda_restart();
> >  #endif
> > -#ifdef CONFIG_ADB_PMU68K
> > -       } else if (macintosh_config->adb_type == MAC_ADB_PB1
> > -               || macintosh_config->adb_type == MAC_ADB_PB2) {
> > +#ifdef CONFIG_ADB_PMU
> > +       } else if (macintosh_config->adb_type == MAC_ADB_PB2) {
> >                 pmu_restart();
> >  #endif
> >         } else if (CPU_IS_030) {
> 

The stability problem here is bigger than just pmu_restart() and 
pmu_shutdown(), so those hunks are insufficient. You need to prevent the 
via-pmu68k driver from loading in the first place and to drop all the 
PMU_68K_V1 cases.

But splitting this patch in that way creates potential merge conflicts, 
which is a hassle. E.g. this hunk:

-       ....
-       switch (macintosh_config->adb_type) {
-       case MAC_ADB_PB1:
-               pmu_kind = PMU_68K_V1;
-               break;
-       case MAC_ADB_PB2:
-               pmu_kind = PMU_68K_V2;
-               break;
-       default:
-               pmu_kind = PMU_UNKNOWN;
-               return -ENODEV;
-       }
-       ...

would get split over two patches.

The way I see it, having no PMU driver for PMU_68K_V1 machines is a bug. 
And loading any of the existing PMU drivers on that hardware is also a 
bug. These bugs are equivalent in that either one means you can't use the 
keyboard, trackpad etc. So there's no value in cherry-picking the other 
bug.

If you are using v4.17 on a PMU_68K_V1 machine, you probably already have 
CONFIG_ADB_PMU68K=n. With that config, here's nothing to be gained from 
bisecting these changes.

Does that make sense? Did I overlook other possible reason(s) to split up 
this patch?

--