serdev: Add ACPI devices by ResourceSource field

serdev: Add ACPI devices by ResourceSource field

When registering a serdev controller, ACPI needs to be checked for
devices attached to it. Currently, all immediate children of the ACPI
node of the controller are assumed to be UART client devices for this
controller. Furthermore, these devices are not searched elsewhere.

This is incorrect: Similar to SPI and I2C devices, the UART client
device definition (via UARTSerialBusV2) can reside anywhere in the ACPI
namespace as resource definition inside the _CRS method and points to
the controller via its ResourceSource field. This field may either
contain a fully qualified or relative path, indicating the controller
device. To address this, we need to walk over the whole ACPI namespace,
looking at each resource definition, and match the client device to the
controller via this field.

This patch is based on the existing acpi serial bus implementations in
drivers/i2c/i2c-core-acpi.c and drivers/spi/spi.c, specifically commit
c2f08a4aec68536b45d92658e5d196fd25491c5b ("spi/acpi: enumerate all SPI
slaves in the namespace").

Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Tested-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20190924162226.1493407-1-luzmaximilian@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>