On Thu, Sep 30, 2021 at 9:30 AM Tony Lindgren <tony@xxxxxxxxxxx> wrote: > > If the serial driver implements PM runtime with autosuspend, the port may > be powered down on TX. To wake up the port, let's add new wakeup() call > for serial drivers to implement as needed. We can call wakeup() from > __uart_start() and flow control related functions before attempting to > write to the serial port registers. > > Let's keep track of the serial port with a new runtime_suspended flag > that the device driver runtime PM suspend and resume can manage with > atomic_set(). This is because only the device driver knows what the > device runtime PM state as in Documentation/power/runtime_pm.rst > under "9. Autosuspend, or automatically-delayed suspend" for locking. > > To allow the serial port drivers to send out pending tx on runtime PM > resume, let's add start_pending_tx() as suggested by Johan Hovold > <johan@xxxxxxxxxx>. ... > + wakeup(port) > + Wake up port if it has been runtime PM suspended. > + > + Locking: port->lock taken. > + > + Interrupts: locally disabled. > + This call must not sleep If it's suspended via ACPI methods, it can't be resumed here, right? Only what we can do is to schedule a resume, but it means we may not access registers immediately after and we have to be sure that the device is resumed. Dead end? -- With Best Regards, Andy Shevchenko
