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Intel stress tests reported issues with the clock stop mode, specifically when trying to do a system suspend while the link is already pm_runtime suspended. In this case, we need to disable the shim wake, but when the PCI parent device is also pm_runtime suspended the SHIM registers are not accessible. Since this is an invalid corner case, this patch suggests a pm_runtime resume of the entire bus to full power (parent+child devices) before the system suspend so that the shim wake can be disabled. Unlike the suspend operation, the .prepare callbacks are propagated from root device to leaf devices. By adding a .prepare callback at the SoundWire link level, we can double-check the pm_runtime status of the device as well as its parent PCI device. When the problematic configuration is detected, the device is pm_runtime resumed - which by construction also resume its parent. An additional loop is added to resume all child devices. In theory we only need to restart the link, but doing so will also cause the physical devices to synchronize and re-initialize, while their Linux devices remain pm_runtime suspended. It's simpler to make sure the codec devices are fully resumed so that we don't have to deal with zombie states. This additional loop could have been avoided by adding a .prepare callback in SoundWire codec drivers. Functionally this would have been equivalent. The rationale for implementing a loop at the link level is only to reduce the amount of code required to deal at the codec level with an Intel corner case - in other words keep codec drivers independent from Intel platform-specific programming sequences. BugLink: https://github.com/thesofproject/linux/issues/2606 Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com> Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com> Link: https://lore.kernel.org/r/20210818024954.16873-4-yung-chuan.liao@linux.intel.com Signed-off-by: Vinod Koul <vkoul@kernel.org>
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.