linux-kernel - Re: [PATCH v11 1/1] serial: core: Start managing serial controllers to enable runtime PM

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Message-ID: <20230514054122.GH14287@atomide.com>
Date:   Sun, 14 May 2023 08:41:22 +0300
From:   Tony Lindgren <tony@...mide.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Jiri Slaby <jirislaby@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...el.com>,
        Dhruva Gole <d-gole@...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,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org
Subject: Re: [PATCH v11 1/1] serial: core: Start managing serial controllers
 to enable runtime PM

* Greg Kroah-Hartman <gregkh@...uxfoundation.org> [230513 11:10]:
> On Thu, May 11, 2023 at 09:53:51AM +0300, 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 bus and 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.
> > 
> > With the serial core port device we can now flush pending TX on the
> > runtime PM resume as suggested by Johan.
> 
> Much better, thanks!
> 
> One thing jumps out at me though, you are passing around "raw" struct
> device pointers as the serial port structure, why?
> 
> Shouldn't:
> 
> > @@ -563,7 +564,8 @@ struct uart_port {
> >  	unsigned int		minor;
> >  	resource_size_t		mapbase;		/* for ioremap */
> >  	resource_size_t		mapsize;
> > -	struct device		*dev;			/* parent device */
> > +	struct device		*dev;			/* serial port physical parent device */
> > +	struct device		*port_dev;		/* serial core port device */
> 
> port_dev here be something like "struct serial_port" (or some better
> name)?  That way you enforce the type being passed around to the serial
> code in this change which will help catch any type mistakes.
> 
> Yes, this structure can just be a "wrapper" around 'struct device' but
> at least it's a unique type.

Good idea thanks, will change.

> Or am I missing why this was done this way?

No reason to keep it as struct device.

Regards,

Tony