linux-kernel - Re: [RESEND PATCH v1 0/5] Solve postboot supplier cleanup and optimize probe ordering

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Date:   Tue, 25 Jun 2019 21:30:52 -0700
From:   Sandeep Patil <sspatil@...roid.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Saravana Kannan <saravanak@...gle.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        David Collins <collinsd@...eaurora.org>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...roid.com
Subject: Re: [RESEND PATCH v1 0/5] Solve postboot supplier cleanup and
 optimize probe ordering

On Tue, Jun 25, 2019 at 11:53:13AM +0800, Greg Kroah-Hartman wrote:
> On Mon, Jun 24, 2019 at 03:37:07PM -0700, Sandeep Patil wrote:
> > We are trying to make sure that all (most) drivers in an Aarch64 system can
> > be kernel modules for Android, like any other desktop system for
> > example. There are a number of problems we need to fix before that happens
> > ofcourse.
> 
> I will argue that this is NOT an android-specific issue.  If the goal of
> creating an arm64 kernel that will "just work" for a wide range of
> hardware configurations without rebuilding is going to happen, we need
> to solve this problem with DT.  This goal was one of the original wishes
> of the arm64 development effort, let's not loose sight of it as
> obviously, this is not working properly just yet.

I believe the proposed solution in this patch series is just that. I am not
sure what the alternatives are. The alternative suggested was to reuse
pre-existing dt-bindings for dependency based probe re-ordering and resolution.

However, it seems we had no way to *really* check if these dependencies are
the real. So, a device may or may not actually depend on the other device for
probe / initialization when the dependency is mentioned in it's dt node. From
DT's point of view, there is no way to tell this ..

I don't know how this is handled in x86. With DT, I don't see how we can do
this unless DT dependencies are _really_ tied with runtime dependencies (The
cycles would have been apparent if that was the case.

Honestly, the "depends-on" property suggested here just piles on to the
existing state. So, it is somewhat doubling the exiting bindings. It says,
you must use depends-on property to define probe / initialization dependency.
The existing bindings like 'clock', 'interrupt', '*-supply' do not enforce
that right now, so you will have device nodes that have these bindings right
now but don't necessarily need them for successful probe for example.

> 
> It just seems that Android is the first one to actually try and
> implement that goal :)

I guess :)

- ssp

> 
> thanks,
> 
> greg k-h