Re: [PATCH v7 1/1] serial: core: Start managing serial controllers to enable runtime PM

[Andy Shevchenko <andriy.shevchenko@intel.com>]

On Tue, Mar 14, 2023 at 09:35:59AM +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 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.

> We need to also update the documentation a bit as suggested by Andy.

Now this can be moved to the comments section (below '---' cutter)
with perhaps addition why it's not done yet.

> With the serial core port device we can now flush pending TX on the

...

> +	return (strncmp(dev_name(dev), drv->name, len) == 0);

Outer parentheses are redundant. The ' == 0' can be replaced with !,
but it's up to you.

...

> +struct serial_base_device *serial_base_device_add(struct uart_port *port,
> +						  const char *name,
> +						  struct device *parent_dev)
> +{
> +	struct serial_base_device *dev;

Can we call this variable (and perhaps everywhere else) like sbd, or sbdev?

This will help to distinguish core device operations and serial one, because,
for example, I have stumbled over kfree(dev) and puzzled a lot.

> +	int err, id;
> +
> +	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
> +	if (!dev)
> +		return NULL;
> +
> +	device_initialize(&dev->dev);
> +	dev->dev.parent = parent_dev;
> +	dev->dev.bus = &serial_base_bus_type;

Who should provide a ->release() callback?

> +	if (str_has_prefix(name, "ctrl")) {
> +		id = port->ctrl_id;
> +	} else {
> +		id = port->line;
> +		dev->port = port;
> +	}
> +
> +	err = dev_set_name(&dev->dev, "%s.%s.%d", name, dev_name(port->dev), id);
> +	if (err)
> +		goto err_free_dev;
> +
> +	err = device_add(&dev->dev);
> +	if (err)
> +		goto err_free_name;
> +
> +	return dev;
> +
> +err_free_name:
> +	kfree_const(dev->dev.kobj.name);

It's still missing put_device() call as suggested by device_add() kernel
documentation. (Double) check also the removal path.

> +err_free_dev:
> +	kfree(dev);

> +	return NULL;
> +}

...

> +struct device;

Since you are embedding the device object this won't suffice,
you need to include device.h.

> +struct uart_driver;
> +struct uart_port;
> +
> +struct serial_base_device {
> +	struct device dev;
> +	struct uart_port *port;
> +};
> +
> +#define to_serial_base_device(x) container_of((x), struct serial_base_device, dev)

container_of.h

...

> +	/* Increment the runtime PM usage count for the active check below */
> +	err = pm_runtime_get(port_dev);

The question here is why don't we need to actually turn on the device immediately
(sync) if it's not already powered?

> +	if (err < 0) {
> +		pm_runtime_put_noidle(port_dev);
> +		return;
> +	}

> +	/*
> +	 * Start TX if enabled, and kick runtime PM. Otherwise we must
> +	 * wait for a retry. See also serial_port.c for runtime PM
> +	 * autosuspend timeout.
> +	 */

I.o.w. does the start_tx() require device to be powered on at this point?

> +	if (pm_runtime_active(port_dev))
>  		port->ops->start_tx(port);
> +	pm_runtime_mark_last_busy(port_dev);
> +	pm_runtime_put_autosuspend(port_dev);

...

> +++ b/drivers/tty/serial/serial_ctrl.c
> @@ -0,0 +1,69 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +
> +/*
> + * Serial core controller driver
> + *
> + * This driver manages the serial core controller struct device instances.
> + * The serial core controller devices are children of the physical serial
> + * port device.
> + */
> +
> +#include <linux/module.h>
> +#include <linux/pm_runtime.h>
> +#include <linux/serial_core.h>

Include for the struct device_driver?

Do we need a separete include for EXPORT_SYMBOL_NS()?

...

> +/*
> + * Serial core port device driver
> + */
> +#include <linux/module.h>
> +#include <linux/pm_runtime.h>
> +#include <linux/serial_core.h>

Similar questions.

+ spinlock.h?

...

> +static __maybe_unused DEFINE_RUNTIME_DEV_PM_OPS(serial_port_pm,

Do you still need __maybe_unused?

> +						NULL,
> +						serial_port_runtime_resume,
> +						NULL);

-- 
With Best Regards,
Andy Shevchenko