diff --git a/drivers/gpio/TODO b/drivers/gpio/TODO new file mode 100644 index 000000000000..19d27c904916 --- /dev/null +++ b/drivers/gpio/TODO @@ -0,0 +1,109 @@ +This is a place for planning the ongoing long-term work in the GPIO +subsystem. + + +GPIO descriptors + +Starting with commit 79a9becda894 the GPIO subsystem embarked on a journey +to move away from the global GPIO numberspace and toward a decriptor-based +approach. This means that GPIO consumers, drivers and machine descriptions +ideally have no use or idea of the global GPIO numberspace that has/was +used in the inception of the GPIO subsystem. + +Work items: + +- Convert all GPIO device drivers to only #include + +- Convert all consumer drivers to only #include + +- Convert all machine descriptors in "boardfiles" to only + #include , the other option being to convert it + to a machine description such as device tree, ACPI or fwnode that + implicitly does not use global GPIO numbers. + +- When this work is complete (will require some of the items in the + following ongoing work as well) we can delete the old global + numberspace accessors from and eventually delete + altogether. + + +Get rid of + +This header and helpers appeared at one point when there was no proper +driver infrastructure for doing simpler MMIO GPIO devices and there was +no core support for parsing device tree GPIOs from the core library with +the [devm_]gpiod_get() calls we have today that will implicitly go into +the device tree back-end. + +Work items: + +- Get rid of struct of_mm_gpio_chip altogether: use the generic MMIO + GPIO for all current users (see below). Delete struct of_mm_gpio_chip, + to_of_mm_gpio_chip(), of_mm_gpiochip_add_data(), of_mm_gpiochip_add() + of_mm_gpiochip_remove() from the kernel. + +- Change all consumer drivers that #include to + #include and stop doing custom parsing of the + GPIO lines from the device tree. This can be tricky and often ivolves + changing boardfiles, etc. + +- Pull semantics for legacy device tree (OF) GPIO lookups into + gpiolib-of.c: in some cases subsystems are doing custom flags and + lookups for polarity inversion, open drain and what not. As we now + handle this with generic OF bindings, pull all legacy handling into + gpiolib so the library API becomes narrow and deep and handle all + legacy bindings internally. (See e.g. commits 6953c57ab172, + 6a537d48461d etc) + +- Delete when all the above is complete and everything + uses or instead. + + +Collect drivers + +Collect GPIO drivers from arch/* and other places that should be placed +in drivers/gpio/gpio-*. Augment platforms to create platform devices or +similar and probe a proper driver in the gpiolib subsystem. + +In some cases it makes sense to create a GPIO chip from the local driver +for a few GPIOs. Those should stay where they are. + + +Generic MMIO GPIO + +The GPIO drivers can utilize the generic MMIO helper library in many +cases, and the helper library should be as helpful as possible for MMIO +drivers. (drivers/gpio/gpio-mmio.c) + +Work items: + +- Look over and identify any remaining easily converted drivers and + dry-code conversions to MMIO GPIO for maintainers to test + +- Expand the MMIO GPIO or write a new library for port-mapped I/O + helpers (x86 inb()/outb()) and convert port-mapped I/O drivers to use + this with dry-coding and sending to maintainers to test + + +GPIOLIB irqchip + +The GPIOLIB irqchip is a helper irqchip for "simple cases" that should +try to cover any generic kind of irqchip cascaded from a GPIO. + +- Look over and identify any remaining easily converted drivers and + dry-code conversions to gpiolib irqchip for maintainers to test + +- Support generic hierarchical GPIO interrupts: these are for the + non-cascading case where there is one IRQ per GPIO line, there is + currently no common infrastructure for this. + + +Increase integration with pin control + +There are already ways to use pin control as back-end for GPIO and +it may make sense to bring these subsystems closer. One reason for +creating pin control as its own subsystem was that we could avoid any +use of the global GPIO numbers. Once the above is complete, it may +make sense to simply join the subsystems into one and make pin +multiplexing, pin configuration, GPIO, etc selectable options in one +and the same pin control and GPIO subsystem.