Re: [RFC PATCH 1/3] UART: Add UART subsystem as a bus.

[Mika Westerberg <mika.westerberg@linux.intel.com>]

On Mon, Dec 03, 2012 at 11:39:59AM +0800, Lv Zheng wrote:
> kobject attribute files:
> # cat /sys/bus/uart/devices/INTF001:00/modalias
> uart:INTF001:00
> # cat /sys/bus/uart/devices/INTF001:00/tty_dev
> ttyS0
> # cat /sys/bus/uart/devices/INTF001:00/tty_attrs
> 115200 8N0 HW
> # cat /sys/bus/uart/devices/INTF001:00/modem_lines
> LE:RTS,CTS,

What if instead of exporting these to userspace we just set the defaults
based on the UartSerialBus() value? This way the user only needs to find the
right tty to pass to hciattach.

> kobject sysfs links:
> # ls -l /sys/bus/uart/devices
> INTF001:00 -> ../../../devices/platform/INTF000:00/INTF001:00
> # ls -l /sys/devices/platform/INTF000:00/INTF001:00
> subsystem -> ../../../../bus/uart
> host_node -> ../tty/ttyS0
> # ls -l /sys/devices/platform/INTF000:00/tty/ttyS0
> target_node -> ../../INTF001:00

And if we have enumerated the UART controller from ACPI (it is probably
attached to the platform bus) we can find the tty device it exports like:

/sys/bus/platform/devices/INTF000:00/tty/ttyS1/dev

Only thing that is missing then is the type of the connected device. That
can be extracted by following the firmware_node symlink:

# ls /sys/bus/platform/devices/INTF000\:00/firmware_node/
INTF001:00
...

# cat  /sys/bus/platform/devices/INTF000\:00/firmware_node/INTF001:00/hid
INTF001

This ACPI ID then can be used to find out what device it is.

Well, this is probably not the simplest solution :-) I'm just trying to
understand why we need to add a new bus type if only thing it adds is the
sysfs files.

> +/**
> + * uart_unregister_device - unregister a UART device
> + * @device: value returned from uart_register_device()
> + *
> + * Reverse effect of uart_register_device().
> + */
> +void uart_unregister_device(struct uart_device *udev)
> +{
> +	if (udev->adap)
> +		klist_del(&udev->klist_parent);
> +	sysfs_remove_link(&udev->dev.kobj, "host_node");
> +	if (udev->tty)
> +		sysfs_remove_link(&udev->tty->kobj, "target_node");
> +	device_unregister(&udev->dev);
> +}
> +EXPORT_SYMBOL_GPL(uart_unreigster_device);

Typo in the function name.