On Thu, 2016-11-03 at 17:29 +0100, Sebastian Andrzej Siewior wrote:
> On 2016-11-03 18:14:23 [+0200], Andy Shevchenko wrote:
> > We can't and basically don't need to call runtime PM in IRQ handler.
> > If IRQ is
> > ours, device must be powered on. Otherwise check if the device is
> > powered off
> > and return immediately.
>
> The old beagle board does PM put once it does not use the UART anymore
> /
> the UART is idle.
And how can it generate interrupts?
> You need to PM get the device even if the device is not yet suspended
> because it might get suspended in the middle of your operation (maybe
> not while you serve the IRQ but we have threaded interrupts).
I grepped code and found no driver under 8250 which is using threaded
IRQ handler. What did I miss?
> If the HW is off then it will be woken by an RX interrupt and I think
> it
> is a different one (I remember Tony wanted to rework that part so that
> the device/UART does not need to care about that).
Rx interrupt from other device?
Or OMAP UART has inbound wake source?
>
> This should work in general but I think that is racy with threaded
> interrupts: What stops the PM core to shutdown the HW before
> serial_port_in() ?
Basically what I understand from this the question is: "Is
pm_runtime_suspended() synchronous with regard to
pm_runtime_get()/pm_runtime_suspend()?".
>
> Sebastian
>
> > Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> > ---
> > drivers/tty/serial/8250/8250_port.c | 16 +++++++++-------
> > 1 file changed, 9 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/tty/serial/8250/8250_port.c
> > b/drivers/tty/serial/8250/8250_port.c
> > index b3f00aa..0c94e82 100644
> > --- a/drivers/tty/serial/8250/8250_port.c
> > +++ b/drivers/tty/serial/8250/8250_port.c
> > @@ -1834,17 +1834,19 @@ EXPORT_SYMBOL_GPL(serial8250_handle_irq);
> >
> > static int serial8250_default_handle_irq(struct uart_port *port)
> > {
> > - struct uart_8250_port *up = up_to_u8250p(port);
> > unsigned int iir;
> > - int ret;
> >
> > - serial8250_rpm_get(up);
> > + /*
> > + * The IRQ might be shared with other peripherals so we
> > must first
> > + * check that are we RPM suspended or not. If we are we
> > assume that
> > + * the IRQ was not for us (we shouldn't be RPM suspended
> > when the
> > + * interrupt is enabled).
> > + */
> > + if (pm_runtime_suspended(port->dev))
> > + return 0;
> >
> > iir = serial_port_in(port, UART_IIR);
> > - ret = serial8250_handle_irq(port, iir);
> > -
> > - serial8250_rpm_put(up);
> > - return ret;
> > + return serial8250_handle_irq(port, iir);
> > }
> >
> > /*
> > --
> > 2.9.3
> >
--
Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Intel Finland Oy
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