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fujitsu-laptop registers two ACPI drivers: one for ACPI device FUJ02B1 enabling backlight control and another for ACPI device FUJ02E3 which handles various other stuff (hotkeys, LEDs, etc.) In a perfect world, private data used by each of these drivers would be neatly encapsulated in a structure specific to a given driver instance. Sadly, firmware present on some Fujitsu laptops makes that impossible by exposing backlight power control (which is what the FUJ02B1 ACPI device should take care of) through the FUJ02E3 ACPI device. This means the backlight driver needs a way to access an ACPI device it is not bound to. When the backlight driver is extracted into a separate module, it will not be able to rely on a module-wide variable any more and such access will happen through an API exposed by fujitsu-laptop. For all known firmwares out in the wild, it seems that whenever the FUJ02B1 ACPI device is present, it is always accompanied by a single instance of the FUJ02E3 ACPI device. We could independently grab an ACPI handle to the FUJ02E3 ACPI device from the backlight driver, but that would require using a hardcoded absolute path to that ACPI device, which is subject to change. It is easier to simply store a module-wide pointer to the last (most likely only) FUJ02E3 ACPI device found, make the aforementioned API use it and cover our bases by warning the user if firmware exposes multiple FUJ02E3 ACPI devices. Introducing this pointer in advance allows us to get rid of the acpi_handle field of struct fujitsu_bl and also enables a bit more step-by-step migration to a device-specific implementation of call_fext_func(). Signed-off-by: Michał Kępień <kernel@kempniu.pl> Reviewed-by: Jonathan Woithe <jwoithe@just42.net> Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org> |
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Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.