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From: Guan-Yu Lin <guanyulin@google.com>
Date: Mon, 26 Feb 2024 17:45:00 +0800
Message-ID: <CAOuDEK1NdFSZgy8_ebO_zSxbU-gLJHsCzjd6JSr2cckQAFgaTg@mail.gmail.com>
Subject: Re: [PATCH v3] PM / core: conditionally skip system pm in
 device/driver model
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: pavel@ucw.cz, len.brown@intel.com, gregkh@linuxfoundation.org, 
	andriy.shevchenko@linux.intel.com, petr.tesarik.ext@huawei.com, 
	rdunlap@infradead.org, james@equiv.tech, broonie@kernel.org, 
	james.clark@arm.com, masahiroy@kernel.org, linux-kernel@vger.kernel.org, 
	linux-pm@vger.kernel.org
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On Sat, Feb 24, 2024 at 1:44=E2=80=AFAM Rafael J. Wysocki <rafael@kernel.or=
g> wrote:
>
> On Fri, Feb 23, 2024 at 3:38=E2=80=AFPM Guan-Yu Lin <guanyulin@google.com=
> wrote:
> >
> > In systems with a main processor and a co-processor, asynchronous
> > controller management can lead to conflicts.  One example is the main
> > processor attempting to suspend a device while the co-processor is
> > actively using it. To address this, we introduce a new sysfs entry
> > called "conditional_skip". This entry allows the system to selectively
> > skip certain device power management state transitions. To use this
> > feature, set the value in "conditional_skip" to indicate the type of
> > state transition you want to avoid.  Please review /Documentation/ABI/
> > testing/sysfs-devices-power for more detailed information.
> >
> > Signed-off-by: Guan-Yu Lin <guanyulin@google.com>
>
> Please explain how this is intended to work.  That is, what exactly
> you expect to happen when the new attribute is set.

The sysfs entry 'conditional_skip' for a device indicates which power
transitions (e.g. PM_EVENT_SUSPEND) are omitted within the system
power management flow. During the processing of an identified power
transition, the device's power.entry will not be added to the
dpm_prepared_list, preventing the device from undergoing that
transition. As 'conditional_skip' is modifiable at runtime, a device's
participation in system power management can be dynamically enabled or
disabled.