Re: [PATCH v12 1/1] serial: core: Start managing serial controllers to enable runtime PM

[Maximilian Luz]

On 10/3/23 14:21, Tony Lindgren wrote:
> * Tony Lindgren <tony@xxxxxxxxxxx> [231003 12:15]:
> > Hi,
> >
> > * Maximilian Luz <luzmaximilian@xxxxxxxxx> [231003 11:57]:
> > > A bad workaround is to disable runtime PM, e.g. via
> > >
> > >    echo on > /sys/bus/serial-base/devices/dw-apb-uart.4:0/dw-apb-uart.4:0.0/power/control
> >
> > If the touchscreen controller driver(s) are using serdev they are
> > children of the dw-apb-uart.4:0.0 and can use runtime PM calls to
> > block the parent device from idling as necessary. The hierarchy
> > unless changed using ignore_children.
>
> Sorry about all the typos, I meant "the hierarchy works unless changed"
> above. The rest of the typos are easier to decipher probably :)

Unfortunately that doesn't quite line up with what I can see on v6.5.5. The
serdev controller seems to be a child of dw-apb-uart.4, a platform device. The
serial-base and serdev devices are siblings. According to sysfs:

    /sys/bus/platform/devices/dw-apb-uart.4
    ├── driver -> ../../../../bus/platform/drivers/dw-apb-uart
    ├── subsystem -> ../../../../bus/platform
    │
    ├── dw-apb-uart.4:0
    │  ├── driver -> ../../../../../bus/serial-base/drivers/ctrl
    │  ├── subsystem -> ../../../../../bus/serial-base
    │  │
    │  └── dw-apb-uart.4:0.0
    │     ├── driver -> ../../../../../../bus/serial-base/drivers/port
    │     └── subsystem -> ../../../../../../bus/serial-base
    │
    └── serial0
       ├── subsystem -> ../../../../../bus/serial
       │
       └── serial0-0
          ├── driver -> ../../../../../../bus/serial/drivers/surface_serial_hub
          └── subsystem -> ../../../../../../bus/serial

Runtime suspend on serial0-0 is disabled/not set up at all. So I assume that if
it were a descendent of dw-apb-uart.4:0.0, things should have worked
out-of-the-box.

Regards,
Max