linux-kernel - Re: [RFC PATCH v4 1/1] serial: core: Start managing serial controllers to enable runtime PM

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Date:   Thu, 8 Dec 2022 11:12:14 +0200 (EET)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Tony Lindgren <tony@...mide.com>
cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Shevchenko <andriy.shevchenko@...el.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        Johan Hovold <johan@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Vignesh Raghavendra <vigneshr@...com>,
        linux-serial <linux-serial@...r.kernel.org>,
        linux-omap@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v4 1/1] serial: core: Start managing serial controllers
 to enable runtime PM

On Wed, 7 Dec 2022, 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.
> With the serial core port device we can now flush pending TX on the
> runtime PM resume as suggested by Johan.
> 
> Suggested-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Suggested-by: Jiri Slaby <jirislaby@...nel.org>
> Suggested-by: Johan Hovold <johan@...nel.org>
> Signed-off-by: Tony Lindgren <tony@...mide.com>
> ---
> 
> Changes since v3:
> 
> - Simplify things by adding a serial core control device as the child of
>   the physical serial port as suggested by Jiri
> 
> - Drop the tinkering of the physical serial port device for runtime PM.
>   Serial core just needs to manage port->port_dev with the addition of
>   the serial core control device and the device hierarchy will keep the
>   pysical serial port device enabled as needed
> 
> - Simplify patch description with all the runtime PM tinkering gone
> 
> - Coding style improvments as noted by Andy
> 
> - Post as a single RFC patch as we're close to the merge window
> 
> Changes since v2:
> 
> - Make each serial port a proper device as suggested by Greg. This is
>   a separate patch that flushes the TX on runtime PM resume
> 
> Changes since v1:
> 
> - Use kref as suggested by Andy
> 
> - Fix memory leak on error as noted by Andy
> 
> - Use use unsigned char for supports_autosuspend as suggested by Andy
> 
> - Coding style improvments as suggested by Andy
> 
> ---

> +	ret = serial_core_add_one_port(drv, port);
> +	if (ret)
> +		return ret;
> +
> +	mutex_lock(&port_mutex);
> +
> +	/* Inititalize a serial core controller device if needed */
> +	ctrl_dev = serial_core_ctrl_find(drv, port->dev, port->ctrl_id);
> +	if (!ctrl_dev) {
> +		ctrl_dev = serial_core_ctrl_device_add(port);
> +		if (!ctrl_dev)
> +			goto err_remove_port;
> +		allocated = true;
> +	}
> +
> +	/* Initialize a serial core port device */
> +	ret = serial_core_port_device_add(ctrl_dev, port);

How is ->port_dev supposed to work here?

->port_dev is not set until in serial_core_port_device_add() but you made
serial_core_add_one_port() call before that.

-- 
 i.

> +	if (ret)
> +		goto err_del_ctrl_dev;
> +
> +	mutex_unlock(&port_mutex);
> +
> +	return 0;
> +
> +err_del_ctrl_dev:
> +	if (allocated)
> +		platform_device_del(to_platform_device(ctrl_dev));
> +
> +err_remove_port:
> +	mutex_unlock(&port_mutex);
> +
> +	return serial_core_remove_one_port(drv, port);
> +}
> +EXPORT_SYMBOL_NS(serial_core_register_port, SERIAL_CORE);