linux-kernel - Re: [PATCH] serial: core: Fix checks for tx runtime PM state

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Date:   Fri, 6 Oct 2023 10:03:25 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Tony Lindgren <tony@...mide.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>, Dhruva Gole <d-gole@...com>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        John Ogness <john.ogness@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Vignesh Raghavendra <vigneshr@...com>,
        linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
        Maximilian Luz <luzmaximilian@...il.com>
Subject: Re: [PATCH] serial: core: Fix checks for tx runtime PM state

On Fri, Oct 06, 2023 at 10:27:38AM +0300, Tony Lindgren wrote:
> * Andy Shevchenko <andriy.shevchenko@...ux.intel.com> [231005 12:01]:
> > On Thu, Oct 05, 2023 at 10:56:42AM +0300, Tony Lindgren wrote:
> > > The serdev device and the serial core controller devices are siblings of
> > > the serial port hardware device. The runtime PM usage count from serdev
> > 
> > I'm a bit lost in terminology here.
> > AFAIU there are:
> > 1) children of the serial physical device;
> > 2) siblings (to each other).
> > 
> > But may be I mistakenly deciphered the diagram from the previous discussion.
> 
> You're right, so how about:
> 
> The serdev device and the serial core controller devices are children of
> the serial port hardware device. The runtime PM usage count from serdev
> device does not propagate to the serial core device siblings, it only
> propagates to the parent.

That's still not accurate:

 - the serdev device is not a child (but a grandchild) of the serial
   controller
 - the new serial port devices are not "siblings" (but descendants) of
   the serial controller
 - the serdev controller ignores the power state of its children so that
   bit is also incorrect

You just want to describe the fact that the serdev controller runtime PM
state is currently not propagated to your new "devices" that are
descendants to the serial controller.

I'm still not sure why it was implemented this way, or if it is even
correct, but this seems to be the state of things.

Johan