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From: "Rafael J. Wysocki" <rafael@kernel.org>
Date: Thu, 29 Feb 2024 19:01:38 +0100
Message-ID: <CAJZ5v0jYTrHiqwPxAQg8mJpWKBgp8DKjGQ1Vucfy3R0LKeLjGQ@mail.gmail.com>
Subject: Re: [PATCH v3 0/4] Add post-init-providers binding to improve
 suspend/resume stability
To: Saravana Kannan <saravanak@google.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>, Rob Herring <robh+dt@kernel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>, Conor Dooley <conor+dt@kernel.org>, 
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>, "Rafael J. Wysocki" <rafael@kernel.org>, 
	Ard Biesheuvel <ardb@kernel.org>, Frank Rowand <frowand.list@gmail.com>, 
	Daniel Scally <djrscally@gmail.com>, Heikki Krogerus <heikki.krogerus@linux.intel.com>, 
	Sakari Ailus <sakari.ailus@linux.intel.com>, Len Brown <lenb@kernel.org>, kernel-team@android.com, 
	devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, 
	linux-efi@vger.kernel.org, linux-acpi@vger.kernel.org
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On Fri, Feb 23, 2024 at 1:03=E2=80=AFAM Saravana Kannan <saravanak@google.c=
om> wrote:
>
> On Thu, Feb 22, 2024 at 5:34=E2=80=AFAM Andy Shevchenko
> <andriy.shevchenko@linux.intel.com> wrote:
> >
> > On Wed, Feb 21, 2024 at 03:30:20PM -0800, Saravana Kannan wrote:
> > > This patch series adds a "post-init-providers" device tree binding th=
at
> > > can be used to break dependency cycles in device tree and enforce a m=
ore
> > > determinstic probe/suspend/resume order. This will also improve the
> > > stability of global async probing and async suspend/resume and allow =
us
> > > to enable them more easily. Yet another step away from playing initca=
ll
> > > chicken with probing and step towards fully async probing and
> > > suspend/resume.
> >
> > Do you know what is the state of affairs in ACPI? Is there any (similar=
)
> > issue even possible?
>
> I'm not very familiar with ACPI, but I wouldn't be surprised if ACPI
> devices have cyclic dependencies. But then ACPI on a PC doesn't
> typically have as many devices/drivers and ACPI might be hiding the
> dependencies from the kernel. So maybe the possibility of a cycle
> visible to the kernel might be low.
>
> I would really like to see fw_devlink extended to ACPI (it's written
> in a way to make that possible), but don't have enough knowledge to do
> it.

This might happen one day, for example in the _DEP handling context
(for now it is very limited, but I'm not actually sure how much more
capable it needs to be).

I don't think that ACPI will ever need device links between parents
and children, though.

On a related note, RISC-V people seem to want to use it on ACPI
systems for interrupt controller dependency tracking.