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

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Date:   Wed, 7 Dec 2022 22:22:11 +0200
From:   Andy Shevchenko <andriy.shevchenko@...el.com>
To:     Tony Lindgren <tony@...mide.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        Johan Hovold <johan@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Vignesh Raghavendra <vigneshr@...com>,
        linux-serial@...r.kernel.org, linux-omap@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v4 1/1] serial: core: Start managing serial
 controllers to enable runtime PM

On Wed, Dec 07, 2022 at 02:43:05PM +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.
> With the serial core port device we can now flush pending TX on the
> runtime PM resume as suggested by Johan.

...

> +static struct platform_device *serial_core_device_add(struct uart_port *port,
> +						      const char *name,
> +						      struct device *parent_dev,
> +						      void *pdata,
> +						      int pdata_size)
> +{
> +	struct platform_device_info pinfo;

' = {}' can also work instead of memset(), but up to you.

> +	memset(&pinfo, 0, sizeof(pinfo));
> +	pinfo.name = name;
> +	pinfo.id = PLATFORM_DEVID_AUTO;
> +	pinfo.parent = parent_dev;
> +	pinfo.data = pdata;
> +	pinfo.size_data = pdata_size;
> +
> +	return platform_device_register_full(&pinfo);
> +}

...

> +	struct serial_port_platdata pdata;

Ditto.

> +	memset(&pdata, 0, sizeof(pdata));

...

> +int serial_core_register_port(struct uart_driver *drv, struct uart_port *port)
> +{

> +	bool allocated = false;

Not sure why this is needed.

> +	struct device *ctrl_dev;
> +	int ret;
> +
> +	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;
> +	}

Wouldn't be slightly better

	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;

?

> +	/* Initialize a serial core port device */
> +	ret = serial_core_port_device_add(ctrl_dev, port);
> +	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));

Shouldn't you call platform_device_unregister()?

> +err_remove_port:
> +	mutex_unlock(&port_mutex);
> +
> +	return serial_core_remove_one_port(drv, port);
> +}

...

> +	platform_device_del(to_platform_device(port_dev));

Ditto?

...

> +	/* Drop the serial core controller device if no ports are using it */
> +	if (!serial_core_ctrl_find(drv, port->dev, port->ctrl_id))
> +		platform_device_del(to_platform_device(ctrl_dev));

Ditto?

...

> +/* Serial core controller data. Serial port device drivers do not need this. */

Some missing forward declarations?

struct uart_driver:
struct uart_port;

?

...

> +static DEFINE_RUNTIME_DEV_PM_OPS(serial_port_pm, NULL,
> +				 serial_port_runtime_resume, NULL);

Wouldn't be more logical to indent like

static DEFINE_RUNTIME_DEV_PM_OPS(serial_port_pm,
				 NULL, serial_port_runtime_resume,
				 NULL);

?

-- 
With Best Regards,
Andy Shevchenko