TODO - OpenGrok cross reference for /linux-5.10/drivers/gpio/TODO

1 This is a place for planning the ongoing long-term work in the GPIO
5 GPIO descriptors
7 Starting with commit 79a9becda894 the GPIO subsystem embarked on a journey
8 to move away from the global GPIO numberspace and toward a descriptor-based
9 approach. This means that GPIO consumers, drivers and machine descriptions
10 ideally have no use or idea of the global GPIO numberspace that has/was
11 used in the inception of the GPIO subsystem.
16 The underlying motivation for this is that the GPIO numberspace has become
18 establish the numberspace at compile-time, making it hard to add any numbers
19 in the middle (such as if you missed a pin on a chip) without the numberspace
22 Machine descriptions such as device tree or ACPI does not have a concept of the
23 Linux GPIO number as those descriptions are external to the Linux kernel
24 and treat GPIO lines as abstract entities.
26 The runtime-assigned GPIO numberspace (what you get if you assign the GPIO
27 base as -1 in struct gpio_chip) has also became unpredictable due to factors
28 such as probe ordering and the introduction of -EPROBE_DEFER making probe
29 ordering of independent GPIO chips essentially unpredictable, as their base
30 number will be assigned on a first come first serve basis.
32 The best way to get out of the problem is to make the global GPIO numbers
33 unimportant by simply not using them. GPIO descriptors deal with this.
37 - Convert all GPIO device drivers to only #include <linux/gpio/driver.h>
39 - Convert all consumer drivers to only #include <linux/gpio/consumer.h>
41 - Convert all machine descriptors in "boardfiles" to only
42   #include <linux/gpio/machine.h>, the other option being to convert it
43   to a machine description such as device tree, ACPI or fwnode that
44   implicitly does not use global GPIO numbers.
46 - When this work is complete (will require some of the items in the
48   numberspace accessors from <linux/gpio.h> and eventually delete
49   <linux/gpio.h> altogether.
55 driver infrastructure for doing simpler MMIO GPIO devices and there was
58 the device tree back-end. It is legacy and should not be used in new code.
62 - Get rid of struct of_mm_gpio_chip altogether: use the generic  MMIO
63   GPIO for all current users (see below). Delete struct of_mm_gpio_chip,
67 - Change all consumer drivers that #include <linux/of_gpio.h> to
68   #include <linux/gpio/consumer.h> and stop doing custom parsing of the
69   GPIO lines from the device tree. This can be tricky and often ivolves
72 - Pull semantics for legacy device tree (OF) GPIO lookups into
73   gpiolib-of.c: in some cases subsystems are doing custom flags and
80 - Delete <linux/of_gpio.h> when all the above is complete and everything
81   uses <linux/gpio/consumer.h> or <linux/gpio/driver.h> instead.
84 Get rid of <linux/gpio.h>
86 This legacy header is a one stop shop for anything GPIO is closely tied
87 to the global GPIO numberspace. The endgame of the above refactorings will
88 be the removal of <linux/gpio.h> and from that point only the specialized
89 headers under <linux/gpio/*.h> will be used. This requires all the above to
90 be completed and is expected to take a long time.
95 Collect GPIO drivers from arch/* and other places that should be placed
96 in drivers/gpio/gpio-*. Augment platforms to create platform devices or
97 similar and probe a proper driver in the gpiolib subsystem.
99 In some cases it makes sense to create a GPIO chip from the local driver
100 for a few GPIOs. Those should stay where they are.
103 new coming drivers. For example, gpio-ml-ioh should be incorporated into
104 gpio-pch. In similar way gpio-intel-mid into gpio-pxa.
107 Generic MMIO GPIO
109 The GPIO drivers can utilize the generic MMIO helper library in many
111 drivers. (drivers/gpio/gpio-mmio.c)
115 - Look over and identify any remaining easily converted drivers and
116   dry-code conversions to MMIO GPIO for maintainers to test
118 - Expand the MMIO GPIO or write a new library for regmap-based I/O
119   helpers for GPIO drivers on regmap that simply use offsets
120   0..n in some register to drive GPIO lines
122 - Expand the MMIO GPIO or write a new library for port-mapped I/O
123   helpers (x86 inb()/outb()) and convert port-mapped I/O drivers to use
124   this with dry-coding and sending to maintainers to test
129 The GPIOLIB irqchip is a helper irqchip for "simple cases" that should
130 try to cover any generic kind of irqchip cascaded from a GPIO.
132 - Convert all the GPIOLIB_IRQCHIP users to pass an irqchip template,
150   g->irq.name = "my_gpio_irq";
151   g->irq.irq_ack = my_gpio_ack_irq;
152   g->irq.irq_mask = my_gpio_mask_irq;
153   g->irq.irq_unmask = my_gpio_unmask_irq;
154   g->irq.irq_set_type = my_gpio_set_irq_type;
156   /* Get a pointer to the gpio_irq_chip */
157   girq = &g->gc.irq;
158   girq->chip = &g->irq;
159   girq->parent_handler = ftgpio_gpio_irq_handler;
160   girq->num_parents = 1;
161   girq->parents = devm_kcalloc(dev, 1, sizeof(*girq->parents),
163   if (!girq->parents)
164       return -ENOMEM;
165   girq->default_type = IRQ_TYPE_NONE;
166   girq->handler = handle_bad_irq;
167   girq->parents[0] = irq;
172 - Look over and identify any remaining easily converted drivers and
173   dry-code conversions to gpiolib irqchip for maintainers to test
175 - Drop gpiochip_set_chained_irqchip() when all the chained irqchips
178 - Add more infrastructure to make it possible to also pass a threaded
181 - Drop gpiochip_irqchip_add_nested() when all the chained irqchips
187 There are already ways to use pin control as back-end for GPIO and
190 use of the global GPIO numbers. Once the above is complete, it may
192 multiplexing, pin configuration, GPIO, etc selectable options in one
193 and the same pin control and GPIO subsystem.