Commit dc5afd72 authored by Hans de Goede's avatar Hans de Goede
Browse files

platform/x86: Add new get_serdev_controller() helper 



In some cases UART attached devices which require an in kernel driver,
e.g. UART attached Bluetooth HCIs are described in the ACPI tables
by an ACPI device with a broken or missing UartSerialBusV2() resource.

This causes the kernel to create a /dev/ttyS# char-device for the UART
instead of creating an in kernel serdev-controller + serdev-device pair
for the in kernel driver.

The quirk handling in acpi_quirk_skip_serdev_enumeration() makes the kernel
create a serdev-controller device for these UARTs instead of a /dev/ttyS#.

Instantiating the actual serdev-device to bind to is up to pdx86 code,
so far this was handled by the x86-android-tablets code. But since
commit b286f4e8 ("serial: core: Move tty and serdev to be children of
serial core port device") the serdev-controller device has moved in the
device hierarchy from (e.g.) /sys/devices/pci0000:00/8086228A:00/serial0 to
/sys/devices/pci0000:00/8086228A:00/8086228A:00:0/8086228A:00:0.0/serial0 .

This makes this a bit trickier to do and another driver is in the works
which will also need this functionality.

Add a new helper to get the serdev-controller device, so that the new
code for this can be shared.

Fixes: b286f4e8 ("serial: core: Move tty and serdev to be children of serial core port device")
Cc: Tony Lindgren <tony@atomide.com>
Signed-off-by: default avatarHans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20240216201721.239791-3-hdegoede@redhat.com
parent bd8905d7

drivers/platform/x86/serdev_helpers.h

0 → 100644
+80 −0
Original line number Diff line number Diff line 
/* SPDX-License-Identifier: GPL-2.0-or-later */

/*

 * In some cases UART attached devices which require an in kernel driver,

 * e.g. UART attached Bluetooth HCIs are described in the ACPI tables

 * by an ACPI device with a broken or missing UartSerialBusV2() resource.

 *

 * This causes the kernel to create a /dev/ttyS# char-device for the UART

 * instead of creating an in kernel serdev-controller + serdev-device pair

 * for the in kernel driver.

 *

 * The quirk handling in acpi_quirk_skip_serdev_enumeration() makes the kernel

 * create a serdev-controller device for these UARTs instead of a /dev/ttyS#.

 *

 * Instantiating the actual serdev-device to bind to is up to pdx86 code,

 * this header provides a helper for getting the serdev-controller device.

 */

#include <linux/acpi.h>

#include <linux/device.h>

#include <linux/err.h>

#include <linux/printk.h>

#include <linux/sprintf.h>

#include <linux/string.h>



static inline struct device *

get_serdev_controller(const char *serial_ctrl_hid,

		      const char *serial_ctrl_uid,

		      int serial_ctrl_port,

		      const char *serdev_ctrl_name)

{

	struct device *ctrl_dev, *child;

	struct acpi_device *ctrl_adev;

	char name[32];

	int i;



	ctrl_adev = acpi_dev_get_first_match_dev(serial_ctrl_hid, serial_ctrl_uid, -1);

	if (!ctrl_adev) {

		pr_err("error could not get %s/%s serial-ctrl adev\n",

		       serial_ctrl_hid, serial_ctrl_uid);

		return ERR_PTR(-ENODEV);

	}



	/* get_first_physical_node() returns a weak ref */

	ctrl_dev = get_device(acpi_get_first_physical_node(ctrl_adev));

	if (!ctrl_dev) {

		pr_err("error could not get %s/%s serial-ctrl physical node\n",

		       serial_ctrl_hid, serial_ctrl_uid);

		ctrl_dev = ERR_PTR(-ENODEV);

		goto put_ctrl_adev;

	}



	/* Walk host -> uart-ctrl -> port -> serdev-ctrl */

	for (i = 0; i < 3; i++) {

		switch (i) {

		case 0:

			snprintf(name, sizeof(name), "%s:0", dev_name(ctrl_dev));

			break;

		case 1:

			snprintf(name, sizeof(name), "%s.%d",

				 dev_name(ctrl_dev), serial_ctrl_port);

			break;

		case 2:

			strscpy(name, serdev_ctrl_name, sizeof(name));

			break;

		}



		child = device_find_child_by_name(ctrl_dev, name);

		put_device(ctrl_dev);

		if (!child) {

			pr_err("error could not find '%s' device\n", name);

			ctrl_dev = ERR_PTR(-ENODEV);

			goto put_ctrl_adev;

		}



		ctrl_dev = child;

	}



put_ctrl_adev:

	acpi_dev_put(ctrl_adev);

	return ctrl_dev;

}