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Device drivers usually depend on the fact that the devices that they control are suspended in the same order that they were probed in. In most cases this is already guaranteed via deferred probe. However, there's one case where this can still break: if a device is instantiated before a dependency (for example if it appears before the dependency in device tree) but gets probed only after the dependency is probed. Instantiation order would cause the dependency to get probed later, in which case probe of the original device would be deferred and the suspend/resume queue would get reordered properly. However, if the dependency is provided by a built-in driver and the device depending on that driver is controlled by a loadable module, which may only get loaded after the root filesystem has become available, we can be faced with a situation where the probe order ends up being different from the suspend/resume order. One example where this happens is on Tegra186, where the ACONNECT is listed very early in device tree (sorted by unit-address) and depends on BPMP (listed very late because it has no unit-address) for power domains and clocks/resets. If the ACONNECT driver is built-in, there is no problem because it will be probed before BPMP, causing a probe deferral and that in turn reorders the suspend/resume queue. However, if built as a module, it will end up being probed after BPMP, and therefore not result in a probe deferral, and therefore the suspend/resume queue will stay in the instantiation order. This in turn causes problems because ACONNECT will be resumed before BPMP, which will result in a hang because the ACONNECT's power domain cannot be powered on as long as the BPMP is still suspended. Fix this by always reordering devices on successful probe. This ensures that the suspend/resume queue is always in probe order and hence meets the natural expectations of drivers vs. their dependencies. Reported-by: Jonathan Hunter <jonathanh@nvidia.com> Acked-by: Rafael. J. Wysocki <rafael@kernel.org> Signed-off-by: Thierry Reding <treding@nvidia.com> Link: https://lore.kernel.org/r/20201203175756.1405564-1-thierry.reding@gmail.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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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.