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