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Abel Vesa
ae8ac19655
The ->set_performance_state() needs to be called before ->power_on() when a genpd is powered on, and after ->power_off() when a genpd is powered off. Do this in order to let the provider know to which performance state to power on the genpd, on the power on sequence, and also to maintain the performance for that genpd until after powering off, on power off sequence. There is no scenario where a consumer would need its genpd enabled and then its performance state increased. Instead, in every scenario, the consumer needs the genpd to be enabled from the start at a specific performance state. And same logic applies to the powering down. No consumer would need its genpd performance state dropped right before powering down. Now, there are currently two vendors which use ->set_performance_state() in their genpd providers. One of them is Tegra, but the only genpd provider (PMC) that makes use of ->set_performance_state() doesn't implement the ->power_on() or ->power_off(), and so it will not be affected by the ops reversal. The other vendor that uses it is Qualcomm, in multiple genpd providers actually (RPM, RPMh and CPR). But all Qualcomm genpd providers that make use of ->set_performance_state() need the order between enabling ops and the performance setting op to be reversed. And the reason for that is that it currently translates into two different voltages in order to power on a genpd to a specific performance state. Basically, ->power_on() switches to the minimum (enabling) voltage for that genpd, and then ->set_performance_state() sets it to the voltage level required by the consumer. By reversing the call order, we rely on the provider to know what to do on each call, but most popular usecase is to cache the performance state and postpone the voltage setting until the ->power_on() gets called. As for the reason of still needing the ->power_on() and ->power_off() for a provider which could get away with just having ->set_performance_state() implemented, there are consumers that do not (nor should) provide an opp-table. For those consumers, ->set_performance_state() will not be called, and so they will enable the genpd to its minimum performance state by a ->power_on() call. Same logic goes for the disabling. Signed-off-by: Abel Vesa <[email protected]> Reviewed-by: Ulf Hansson <[email protected]> Signed-off-by: Rafael J. Wysocki <[email protected]>
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.