On Fri, May 31, 2024 at 08:09:18AM -0700, Douglas Anderson wrote:
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 problems 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()-based 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. If a serdev device in the kernel needs to block system suspend it should block its own suspend and it can use serdev_device_wait_until_sent() to ensure bytes are 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") Cc: stable@vger.kernel.org Reviewed-by: Tony Lindgren tony.lindgren@linux.intel.com Signed-off-by: Douglas Anderson dianders@chromium.org
...
- /*
* Nothing to do on pm_runtime_force_suspend(), see* DEFINE_RUNTIME_DEV_PM_OPS.
* DEFINE_RUNTIME_DEV_PM_OPS().
(in case you need to send a new version)
*/- if (!pm_runtime_enabled(dev))
return 0;