1This is a place for planning the ongoing long-term work in the GPIO 2subsystem. 3 4 5GPIO descriptors 6 7Starting with commit 79a9becda894 the GPIO subsystem embarked on a journey 8to move away from the global GPIO numberspace and toward a decriptor-based 9approach. This means that GPIO consumers, drivers and machine descriptions 10ideally have no use or idea of the global GPIO numberspace that has/was 11used in the inception of the GPIO subsystem. 12 13Work items: 14 15- Convert all GPIO device drivers to only #include <linux/gpio/driver.h> 16 17- Convert all consumer drivers to only #include <linux/gpio/consumer.h> 18 19- Convert all machine descriptors in "boardfiles" to only 20 #include <linux/gpio/machine.h>, the other option being to convert it 21 to a machine description such as device tree, ACPI or fwnode that 22 implicitly does not use global GPIO numbers. 23 24- When this work is complete (will require some of the items in the 25 following ongoing work as well) we can delete the old global 26 numberspace accessors from <linux/gpio.h> and eventually delete 27 <linux/gpio.h> altogether. 28 29 30Get rid of <linux/of_gpio.h> 31 32This header and helpers appeared at one point when there was no proper 33driver infrastructure for doing simpler MMIO GPIO devices and there was 34no core support for parsing device tree GPIOs from the core library with 35the [devm_]gpiod_get() calls we have today that will implicitly go into 36the device tree back-end. 37 38Work items: 39 40- Get rid of struct of_mm_gpio_chip altogether: use the generic MMIO 41 GPIO for all current users (see below). Delete struct of_mm_gpio_chip, 42 to_of_mm_gpio_chip(), of_mm_gpiochip_add_data(), of_mm_gpiochip_add() 43 of_mm_gpiochip_remove() from the kernel. 44 45- Change all consumer drivers that #include <linux/of_gpio.h> to 46 #include <linux/gpio/consumer.h> and stop doing custom parsing of the 47 GPIO lines from the device tree. This can be tricky and often ivolves 48 changing boardfiles, etc. 49 50- Pull semantics for legacy device tree (OF) GPIO lookups into 51 gpiolib-of.c: in some cases subsystems are doing custom flags and 52 lookups for polarity inversion, open drain and what not. As we now 53 handle this with generic OF bindings, pull all legacy handling into 54 gpiolib so the library API becomes narrow and deep and handle all 55 legacy bindings internally. (See e.g. commits 6953c57ab172, 56 6a537d48461d etc) 57 58- Delete <linux/of_gpio.h> when all the above is complete and everything 59 uses <linux/gpio/consumer.h> or <linux/gpio/driver.h> instead. 60 61 62Collect drivers 63 64Collect GPIO drivers from arch/* and other places that should be placed 65in drivers/gpio/gpio-*. Augment platforms to create platform devices or 66similar and probe a proper driver in the gpiolib subsystem. 67 68In some cases it makes sense to create a GPIO chip from the local driver 69for a few GPIOs. Those should stay where they are. 70 71 72Generic MMIO GPIO 73 74The GPIO drivers can utilize the generic MMIO helper library in many 75cases, and the helper library should be as helpful as possible for MMIO 76drivers. (drivers/gpio/gpio-mmio.c) 77 78Work items: 79 80- Look over and identify any remaining easily converted drivers and 81 dry-code conversions to MMIO GPIO for maintainers to test 82 83- Expand the MMIO GPIO or write a new library for port-mapped I/O 84 helpers (x86 inb()/outb()) and convert port-mapped I/O drivers to use 85 this with dry-coding and sending to maintainers to test 86 87 88GPIOLIB irqchip 89 90The GPIOLIB irqchip is a helper irqchip for "simple cases" that should 91try to cover any generic kind of irqchip cascaded from a GPIO. 92 93- Convert all the GPIOLIB_IRQCHIP users to pass an irqchip template, 94 parent and flags before calling [devm_]gpiochip_add[_data](). 95 Currently we set up the irqchip after setting up the gpiochip 96 using gpiochip_irqchip_add() and gpiochip_set_[chained|nested]_irqchip(). 97 This is too complex, so convert all users over to just set up 98 the irqchip before registering the gpio_chip, typical example: 99 100 /* Typical state container with dynamic irqchip */ 101 struct my_gpio { 102 struct gpio_chip gc; 103 struct irq_chip irq; 104 }; 105 106 int irq; /* from platform etc */ 107 struct my_gpio *g; 108 struct gpio_irq_chip *girq 109 110 /* Set up the irqchip dynamically */ 111 g->irq.name = "my_gpio_irq"; 112 g->irq.irq_ack = my_gpio_ack_irq; 113 g->irq.irq_mask = my_gpio_mask_irq; 114 g->irq.irq_unmask = my_gpio_unmask_irq; 115 g->irq.irq_set_type = my_gpio_set_irq_type; 116 117 /* Get a pointer to the gpio_irq_chip */ 118 girq = &g->gc.irq; 119 girq->chip = &g->irq; 120 girq->parent_handler = ftgpio_gpio_irq_handler; 121 girq->num_parents = 1; 122 girq->parents = devm_kcalloc(dev, 1, sizeof(*girq->parents), 123 GFP_KERNEL); 124 if (!girq->parents) 125 return -ENOMEM; 126 girq->default_type = IRQ_TYPE_NONE; 127 girq->handler = handle_bad_irq; 128 girq->parents[0] = irq; 129 130 When this is done, we will delete the old APIs for instatiating 131 GPIOLIB_IRQCHIP and simplify the code. 132 133- Look over and identify any remaining easily converted drivers and 134 dry-code conversions to gpiolib irqchip for maintainers to test 135 136- Support generic hierarchical GPIO interrupts: these are for the 137 non-cascading case where there is one IRQ per GPIO line, there is 138 currently no common infrastructure for this. 139 140 141Increase integration with pin control 142 143There are already ways to use pin control as back-end for GPIO and 144it may make sense to bring these subsystems closer. One reason for 145creating pin control as its own subsystem was that we could avoid any 146use of the global GPIO numbers. Once the above is complete, it may 147make sense to simply join the subsystems into one and make pin 148multiplexing, pin configuration, GPIO, etc selectable options in one 149and the same pin control and GPIO subsystem. 150