linux-kernel - Re: [PATCH 0/4] platform: allow ATOM PMC code to be optional

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Message-ID: <YmpoeJtFNSyCq1QL@smile.fi.intel.com>
Date:   Thu, 28 Apr 2022 13:12:08 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Paul Gortmaker <paul.gortmaker@...driver.com>
Cc:     linux-kernel@...r.kernel.org,
        Aubrey Li <aubrey.li@...ux.intel.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Len Brown <lenb@...nel.org>, linux-acpi@...r.kernel.org,
        Mark Gross <markgross@...nel.org>,
        platform-driver-x86@...r.kernel.org,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH 0/4] platform: allow ATOM PMC code to be optional

On Thu, Apr 28, 2022 at 02:24:26AM -0400, Paul Gortmaker wrote:
> A few months back I was doing a test build for "defconfig-like" COTS
> hardware and happened to notice some pmc-atom stuff being built.  Fine,
> I thought - the defconfig isn't minimal - we all know that - what Kconfig
> do I use to turn that off?  Well, imagine my surprise when I found out
> you couldn't turn it [Atom Power Management Controller] code off!

Turning it off on BayTrail and CherryTrail devices will be devastating
to the users' experience. And plenty of cheap tablets are exactly made
on that SoCs.

> Normally we all agree to not use "default y" unless unavoidable, but
> somehow this was added as "def_bool y" which is even worse ; you can
> see the Kconfig setting but there is *no* way you can turn it off.
> 
> After investigating, I found no reason why the atom code couldn't be
> opt-out with just minor changes that the original addition overlooked.
> 
> And so this series addreses that.  I tried to be sensitive to not
> break any existing configs in the process, but the defconfig will
> now intentionally be different and exclude this atom specific code.
> 
> Using a defconfig on today's linux-next, here is the delta summary:
> 
> $ ./scripts/bloat-o-meter -c ../pmc-atom-pre/vmlinux ../pmc-atom-post/vmlinux|grep add/remove
> add/remove: 0/410 grow/shrink: 0/7 up/down: 0/-47659 (-47659)
> add/remove: 0/105 grow/shrink: 0/1 up/down: 0/-6848 (-6848)
> add/remove: 0/56 grow/shrink: 0/1 up/down: 0/-10155 (-10155)
> 
> $ ./scripts/bloat-o-meter -c ../pmc-atom-pre/vmlinux ../pmc-atom-post/vmlinux|grep Total
> Total: Before=13626994, After=13579335, chg -0.35%
> Total: Before=3572137, After=3565289, chg -0.19%
> Total: Before=1235335, After=1225180, chg -0.82%
> 
> It is hard to reclaim anything against the inevitable growth in
> footprint, so I'd say we should be glad to take whatever we can.
> 
> Boot tested defconfig on today's linux-next on older non-atom COTS.

I believe this needs an extensive test done by Hans who possesses a lot of
problematic devices that require that module to be present.

Note to all your patches, please, use --cc option instead of putting noisy
lines in the each of the commit messages. For myself I created a "smart"
script [1] to avoid bothering with that. Feel free to use, modify, send PRs
back to improve.

[1]: https://github.com/andy-shev/home-bin-tools/blob/master/ge2maintainer.sh

-- 
With Best Regards,
Andy Shevchenko