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ca84cd379b
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:
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.