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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 b286f4e87e ("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: b286f4e87e ("serial: core: Move tty and serdev to be children of serial core port device")
Cc: Tony Lindgren <tony@atomide.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20240216201721.239791-3-hdegoede@redhat.com
This commit is contained in:
Hans de Goede 2024-02-16 21:17:19 +01:00
parent bd8905d709
commit dc5afd720f
1 changed files with 80 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

80
drivers/platform/x86/serdev_helpers.h Normal file
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/* 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;
}