| Message ID | 20240523162207.1.I2395e66cf70c6e67d774c56943825c289b9c13e4@changeid |
|---|---|
| State | Superseded |
| Headers | show |
| Series | serial: Fix problems when serial transfer is happening at suspend time | expand |
Quoting Douglas Anderson (2024-05-23 16:22:12) > Recently, suspend testing on sc7180-trogdor based devices has started > to sometimes fail with messages like this: > > port a88000.serial:0.0: PM: calling pm_runtime_force_suspend+0x0/0xf8 @ 28934, parent: a88000.serial:0 > port a88000.serial:0.0: PM: dpm_run_callback(): pm_runtime_force_suspend+0x0/0xf8 returns -16 > port a88000.serial:0.0: PM: pm_runtime_force_suspend+0x0/0xf8 returned -16 after 33 usecs > port a88000.serial:0.0: PM: failed to suspend: error -16 > > I could reproduce these problem by logging in via an agetty on the > debug serial port (which was _not_ used for kernel console) and > running: > cat /var/log/messages > ...and then (via an SSH session) forcing a few suspend/resume cycles. > > Tracing through the code and doing some printf debugging shows that > the -16 (-EBUSY) comes from the recently added > serial_port_runtime_suspend(). > > The idea of the serial_port_runtime_suspend() function is to prevent > the port from being _runtime_ suspended if it still has bytes left to > transmit. Having bytes left to transmit isn't a reason to block > _system_ suspend, though. Can you elaborate? I paused to think that maybe we would want to make sure that everything that was transmitted had been transmitted but that doesn't seem right because it's a problem for higher layers to solve, e.g. serdev would want to make sure some sleep command sent over the wire actually got sent. > The DEFINE_RUNTIME_DEV_PM_OPS() used by the > serial_port code means that the system suspend function will be > pm_runtime_force_suspend(). In pm_runtime_force_suspend() we can see > that before calling the runtime suspend function we'll call > pm_runtime_disable(). This should be a reliable way to detect that > we're called from system suspend and that we shouldn't look for > busyness. > > Fixes: 43066e32227e ("serial: port: Don't suspend if the port is still busy") > Signed-off-by: Douglas Anderson <dianders@chromium.org> > --- > > drivers/tty/serial/serial_port.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/drivers/tty/serial/serial_port.c b/drivers/tty/serial/serial_port.c > index 91a338d3cb34..b781227cc996 100644 > --- a/drivers/tty/serial/serial_port.c > +++ b/drivers/tty/serial/serial_port.c > @@ -64,6 +64,16 @@ static int serial_port_runtime_suspend(struct device *dev) > if (port->flags & UPF_DEAD) > return 0; > > + /* > + * We only want to check the busyness of the port if PM Runtime is > + * enabled. Specifically PM Runtime will be disabled by > + * pm_runtime_force_suspend() during system suspend and we don't want > + * to block system suspend even if there is data still left to > + * transmit. We only want to block regulator PM Runtime transitions. s/regulator/regular/ Is this a typo? Also, why is "runtime" capitalized? > + */ > + if (!pm_runtime_enabled(dev)) > + return 0;
diff --git a/drivers/tty/serial/serial_port.c b/drivers/tty/serial/serial_port.c index 91a338d3cb34..b781227cc996 100644 --- a/drivers/tty/serial/serial_port.c +++ b/drivers/tty/serial/serial_port.c @@ -64,6 +64,16 @@ static int serial_port_runtime_suspend(struct device *dev) if (port->flags & UPF_DEAD) return 0; + /* + * We only want to check the busyness of the port if PM Runtime is + * enabled. Specifically PM Runtime will be disabled by + * pm_runtime_force_suspend() during system suspend and we don't want + * to block system suspend even if there is data still left to + * transmit. We only want to block regulator PM Runtime transitions. + */ + if (!pm_runtime_enabled(dev)) + return 0; + uart_port_lock_irqsave(port, &flags); if (!port_dev->tx_enabled) { uart_port_unlock_irqrestore(port, flags);
Recently, suspend testing on sc7180-trogdor based devices has started to sometimes fail with messages like this: port a88000.serial:0.0: PM: calling pm_runtime_force_suspend+0x0/0xf8 @ 28934, parent: a88000.serial:0 port a88000.serial:0.0: PM: dpm_run_callback(): pm_runtime_force_suspend+0x0/0xf8 returns -16 port a88000.serial:0.0: PM: pm_runtime_force_suspend+0x0/0xf8 returned -16 after 33 usecs port a88000.serial:0.0: PM: failed to suspend: error -16 I could reproduce these problem by logging in via an agetty on the debug serial port (which was _not_ used for kernel console) and running: cat /var/log/messages ...and then (via an SSH session) forcing a few suspend/resume cycles. Tracing through the code and doing some printf debugging shows that the -16 (-EBUSY) comes from the recently added serial_port_runtime_suspend(). The idea of the serial_port_runtime_suspend() function is to prevent the port from being _runtime_ suspended if it still has bytes left to transmit. Having bytes left to transmit isn't a reason to block _system_ suspend, though. The DEFINE_RUNTIME_DEV_PM_OPS() used by the serial_port code means that the system suspend function will be pm_runtime_force_suspend(). In pm_runtime_force_suspend() we can see that before calling the runtime suspend function we'll call pm_runtime_disable(). This should be a reliable way to detect that we're called from system suspend and that we shouldn't look for busyness. Fixes: 43066e32227e ("serial: port: Don't suspend if the port is still busy") Signed-off-by: Douglas Anderson <dianders@chromium.org> --- drivers/tty/serial/serial_port.c | 10 ++++++++++ 1 file changed, 10 insertions(+)