On Thu, Sep 30, 2021 at 9:30 AM Tony Lindgren <tony@xxxxxxxxxxx> wrote: > > We can use the wakeup() and uart_start_pending_tx() calls to wake up an > idle serial port and send out the pending TX buffer on runtime PM resume. > This allows us to remove the depedency to pm_runtime_irq_safe() for dependency > 8250_omap driver in the following patches. > > We manage the port runtime_suspended flag in the serial port driver as > only the driver knows when the hardware is runtime PM suspended. Note that > The current flag for rpm_tx_active cannot be used as it is TX specific > for 8250_port. > > We already have serial8250_start_tx() call serial8250_rpm_get_tx(), and > serial8250_stop_tx() call serial8250_rpm_put_tx() to take care of the > runtime PM usage count for TX. To have the serial port driver call > uart_start_pending_tx() on runtime resume, we must now use just > pm_runtime_get() for serial8250_start_tx() instead of the sync version. > > With these changes we must now also flip 8250_omap driver over to call > uart_start_pending_tx(). That's currently the only user of UART_CAP_RPM. Do I understand the flow correctly: 1) if we suspended, we request resume 2) until resume is not fulfilled we return error code to user space to try again ? In this case we have no register access to the powered off device and ACPI, for example, may have a chance to resume the device in a non-atomic way. Is this the correct interpretation? -- With Best Regards, Andy Shevchenko
