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. The numberspace issue is the same as to why irq is moving away from irq numbers to IRQ descriptors. The underlying motivation for this is that the GPIO numberspace has become unmanageable: machine board files tend to become full of macros trying to establish the numberspace at compile-time, making it hard to add any numbers in the middle (such as if you missed a pin on a chip) without the numberspace breaking. Machine descriptions such as device tree or ACPI does not have a concept of the Linux GPIO number as those descriptions are external to the Linux kernel and treat GPIO lines as abstract entities. The runtime-assigned GPIO numberspace (what you get if you assign the GPIO base as -1 in struct gpio_chip) has also became unpredictable due to factors such as probe ordering and the introduction of -EPROBE_DEFER making probe ordering of independent GPIO chips essentially unpredictable, as their base number will be assigned on a first come first serve basis. The best way to get out of the problem is to make the global GPIO numbers unimportant by simply not using them. GPIO descriptors deal with this. 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. It is legacy and should not be used in new code. 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. Get rid of This legacy header is a one stop shop for anything GPIO is closely tied to the global GPIO numberspace. The endgame of the above refactorings will be the removal of and from that point only the specialized headers under will be used. This requires all the above to be completed and is expected to take a long time. 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 regmap-based I/O helpers for GPIO drivers on regmap that simply use offsets 0..n in some register to drive GPIO lines - 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. - Convert all the GPIOLIB_IRQCHIP users to pass an irqchip template, parent and flags before calling [devm_]gpiochip_add[_data](). Currently we set up the irqchip after setting up the gpiochip using gpiochip_irqchip_add() and gpiochip_set_[chained|nested]_irqchip(). This is too complex, so convert all users over to just set up the irqchip before registering the gpio_chip, typical example: /* Typical state container with dynamic irqchip */ struct my_gpio { struct gpio_chip gc; struct irq_chip irq; }; int irq; /* from platform etc */ struct my_gpio *g; struct gpio_irq_chip *girq; /* Set up the irqchip dynamically */ g->irq.name = "my_gpio_irq"; g->irq.irq_ack = my_gpio_ack_irq; g->irq.irq_mask = my_gpio_mask_irq; g->irq.irq_unmask = my_gpio_unmask_irq; g->irq.irq_set_type = my_gpio_set_irq_type; /* Get a pointer to the gpio_irq_chip */ girq = &g->gc.irq; girq->chip = &g->irq; girq->parent_handler = ftgpio_gpio_irq_handler; girq->num_parents = 1; girq->parents = devm_kcalloc(dev, 1, sizeof(*girq->parents), GFP_KERNEL); if (!girq->parents) return -ENOMEM; girq->default_type = IRQ_TYPE_NONE; girq->handler = handle_bad_irq; girq->parents[0] = irq; When this is done, we will delete the old APIs for instatiating GPIOLIB_IRQCHIP and simplify the code. - Look over and identify any remaining easily converted drivers and dry-code conversions to gpiolib irqchip for maintainers to test - Drop gpiochip_set_chained_irqchip() when all the chained irqchips have been converted to the above infrastructure. - Add more infrastructure to make it possible to also pass a threaded irqchip in struct gpio_irq_chip. - Drop gpiochip_irqchip_add_nested() when all the chained irqchips have been converted to the above infrastructure. 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.