linux-kernel - Re: [PATCH] remove CONFIG

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Message-ID: <Yry6XvOGge2xKx/n@zx2c4.com>
Date:   Wed, 29 Jun 2022 22:47:26 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Kalesh Singh <kaleshsingh@...gle.com>
Cc:     Christoph Hellwig <hch@....de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Christian Brauner <brauner@...nel.org>,
        Hridya Valsaraju <hridya@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Theodore Ts'o <tytso@....edu>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "Alex Xu (Hello71)" <alex_y_xu@...oo.ca>,
        Paolo Abeni <pabeni@...hat.com>, Rob Herring <robh@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Josh Triplett <josh@...htriplett.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Shuah Khan <shuah@...nel.org>, linux-kernel@...r.kernel.org,
        wireguard@...ts.zx2c4.com, netdev@...r.kernel.org,
        rcu@...r.kernel.org, linux-kselftest@...r.kernel.org,
        sultan@...neltoast.com
Subject: Re: [PATCH] remove CONFIG_ANDROID

Hi Kalesh,

On Wed, Jun 29, 2022 at 12:05:23PM -0700, Kalesh Singh wrote:
> Thanks for raising this.
> 
> Android no longer uses PM_AUTOSLEEP, is correct. libsuspend is
> also now deprecated. Android autosuspend is initiatiated from the
> userspace system suspend service [1].
> 
> A runtime config sounds more reasonable since in the !PM_AUTOSLEEP
> case, it is userspace which decides the suspend policy.
> 
> [1] https://cs.android.com/android/platform/superproject/+/bf3906ecb33c98ff8edd96c852b884dbccb73295:system/hardware/interfaces/suspend/1.0/default/SystemSuspend.cpp;l=265

Bingo, thanks for the pointer. So looking at this, I'm trying to tease
out some heuristic that wouldn't require any changes, but I don't really
see anything _too_ perfect. One fragment of an idea would be that the
kernel treats things in autosuspending mode if anybody is holding open a
fd to /sys/power/state. But I worry this would interact with
non-autosuspending userspaces that also hold open the file. So barring
that, I'm not quite sure.

If you also can't think of something, maybe we should talk about adding
something that requires code changes. In that line of thinking, how
would you feel about opening /sys/power/userspace_autosuspender and
keeping that fd open. Then the kernel API would have
`bool pm_has_userspace_autosuspender(void)` that code could check.
Alternatively, if you don't want refcounting fd semantics for that, just
writing a "1" into a similar file seems fine?

Any strong opinions about it? Personally it doesn't make much of a
difference to me. The important thing is just that it'd be something
you're willing to implement in that SystemSuspend.cpp file.

Jason