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The SOR resets are exclusively shared with the SOR power domain. This
means that exclusive access can only be granted temporarily and in order
for that to work, a rigorous sequence must be observed. To ensure that a
single consumer gets exclusive access to a reset, each consumer must
implement a rigorous protocol using the reset_control_acquire() and
reset_control_release() functions.
However, these functions alone don't provide any guarantees at the
system level. Drivers need to ensure that the only a single consumer has
access to the reset at the same time. In order for the SOR to be able to
exclusively access its reset, it must therefore ensure that the SOR
power domain is not powered off by holding on to a runtime PM reference
to that power domain across the reset assert/deassert operation.
This used to work fine by accident, but was revealed when recently more
devices started to rely on the SOR power domain.
Fixes: 11c632e1cf ("drm/tegra: sor: Implement acquire/release for reset")
Reported-by: Jonathan Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
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.