linux-kernel - Re: [PATCH v5 1/1] serial: core: Start managing serial controllers to enable runtime PM

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Date:   Thu, 20 Apr 2023 13:34:02 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Tony Lindgren <tony@...mide.com>
Cc:     Jiri Slaby <jirislaby@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...el.com>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        Johan Hovold <johan@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Vignesh Raghavendra <vigneshr@...com>,
        linux-omap@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-serial@...r.kernel.org
Subject: Re: [PATCH v5 1/1] serial: core: Start managing serial controllers
 to enable runtime PM

On Wed, Feb 01, 2023 at 08:38:42AM +0200, Tony Lindgren wrote:
> * Greg Kroah-Hartman <gregkh@...uxfoundation.org> [230131 10:10]:
> > On Mon, Jan 16, 2023 at 09:59:58AM +0200, Tony Lindgren wrote:
> > > We want to enable runtime PM for serial port device drivers in a generic
> > > way. To do this, we want to have the serial core layer manage the
> > > registered physical serial controller devices.
> > > 
> > > To do this, let's set up a struct device for the serial core controller
> > > as suggested by Greg and Jiri. The serial core controller devices are
> > > children of the physical serial port device. The serial core controller
> > > device is needed to support multiple different kind of ports connected
> > > to single physical serial port device.
> > > 
> > > Let's also set up a struct device for the serial core port. The serial
> > > core port instances are children of the serial core controller device.
> > 
> > Looking better, but why is this new device a platform device?  That
> > feels odd, you should never have a platform device hanging off of a
> > non-platform device, right?
> 
> No special need for it to be a platform device. It just is easy to set
> up, and for my test case the serial port physical device is also a
> platform device.
> 
> What's your preference here?

Never make up a "fake" platform device please.  Only use them for real
platform devices.  Use a virtual device if you want a virtual one.

thanks,

greg k-h