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18eeef46d3
The regulator for the touchscreen could be: * A dedicated regulator just for the touchscreen. * A regulator shared with something else in the system. * An always-on regulator. How we want the "reset" line to behave depends a bit on which of those three cases we're in. Currently the code is written with the assumption that it has a dedicated regulator, but that's not really guaranteed to be the case. The problem we run into is that if we leave the touchscreen powered on (because someone else is requesting the regulator or it's an always-on regulator) and we assert reset then we apparently burn an extra 67 mW of power. That's not great. Let's instead tie the control of the reset line to the true state of the regulator as reported by regulator notifiers. If we have an always-on regulator our notifier will never be called. If we have a shared regulator then our notifier will be called when the touchscreen is truly turned on or truly turned off. Using notifiers like this nicely handles all the cases without resorting to hacks like pretending that there is no "reset" GPIO if we have an always-on regulator. NOTE: if the regulator is on a shared line it's still possible that things could be a little off. Specifically, this case is not handled even after this patch: 1. Suspend goodix (send "sleep", goodix stops requesting regulator on) 2. Other regulator user turns off (regulator fully turns off). 3. Goodix driver gets notified and asserts reset. 4. Other regulator user turns on. 5. Goodix driver gets notified and deasserts reset. 6. Nobody resumes goodix. With that set of steps we'll have reset deasserted but we will have lost the results of the I2C_HID_PWR_SLEEP from the suspend path. That means we might be in higher power than we could be even if the goodix driver thinks things are suspended. Presumably, however, we're still in better shape than if we were asserting "reset" the whole time. If somehow the above situation is actually affecting someone and we want to do better we can deal with it when we have a real use case. Signed-off-by: Douglas Anderson <dianders@chromium.org> Signed-off-by: Jiri Kosina <jkosina@suse.cz> |
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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.