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.
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).
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).
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() ?
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
>
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