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According to Section 3.5 of the "Intel Low Power S0 Idle" document [1], Function 5 of the LPS0 _DSM is expected to be invoked when the system configuration matches the criteria for entering the target low-power state of the platform. In particular, this means that all devices should be suspended and in low-power states already when that function is invoked. This is not the case currently, however, because Function 5 of the LPS0 _DSM is invoked by it before the "noirq" phase of device suspend, which means that some devices may not have been put into low-power states yet at that point. That is a consequence of the previous design of the suspend-to-idle flow that allowed the "noirq" phase of device suspend and the "noirq" phase of device resume to be carried out for multiple times while "suspended" (if any spurious wakeup events were detected) and the point of the LPS0 _DSM Function 5 invocation was chosen so as to call it (and LPS0 _DSM Function 6 analogously) once per suspend-resume cycle (regardless of how many times the "noirq" phases of device suspend and resume were carried out while "suspended"). Now that the suspend-to-idle flow has been redesigned to carry out the "noirq" phases of device suspend and resume once in each cycle, the code can be reordered to follow the specification that it is based on more closely. For this purpose, add ->prepare_late and ->restore_early platform callbacks for suspend-to-idle, to be executed, respectively, after the "noirq" phase of suspending devices and before the "noirq" phase of resuming them and make ACPI use them for the invocation of LPS0 _DSM functions as appropriate. While at it, move the LPS0 entry requirements check to be made before invoking Functions 3 and 5 of the LPS0 _DSM (also once per cycle) as follows from the specification [1]. Link: https://uefi.org/sites/default/files/resources/Intel_ACPI_Low_Power_S0_Idle.pdf # [1] Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Tested-by: Kai-Heng Feng <kai.heng.feng@canonical.com> |
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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 Restructured Text 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.