diff options
Diffstat (limited to 'Documentation/driver-api')
| -rw-r--r-- | Documentation/driver-api/early-userspace/buffer-format.rst | 5 | ||||
| -rw-r--r-- | Documentation/driver-api/gpio/board.rst | 65 | ||||
| -rw-r--r-- | Documentation/driver-api/gpio/index.rst | 1 | ||||
| -rw-r--r-- | Documentation/driver-api/gpio/legacy-boards.rst | 298 | ||||
| -rw-r--r-- | Documentation/driver-api/pin-control.rst | 4 |
5 files changed, 371 insertions, 2 deletions
diff --git a/Documentation/driver-api/early-userspace/buffer-format.rst b/Documentation/driver-api/early-userspace/buffer-format.rst index 726bfa2fe70d..4597a91100b7 100644 --- a/Documentation/driver-api/early-userspace/buffer-format.rst +++ b/Documentation/driver-api/early-userspace/buffer-format.rst @@ -86,6 +86,11 @@ c_mtime is ignored unless CONFIG_INITRAMFS_PRESERVE_MTIME=y is set. The c_filesize should be zero for any file which is not a regular file or symlink. +c_namesize may account for more than one trailing '\0', as long as the +value doesn't exceed PATH_MAX. This can be useful for ensuring that a +subsequent file data segment is aligned, e.g. to a filesystem block +boundary. + The c_chksum field contains a simple 32-bit unsigned sum of all the bytes in the data field. cpio(1) refers to this as "crc", which is clearly incorrect (a cyclic redundancy check is a different and diff --git a/Documentation/driver-api/gpio/board.rst b/Documentation/driver-api/gpio/board.rst index 4fd1cbd8296e..069b54d8591b 100644 --- a/Documentation/driver-api/gpio/board.rst +++ b/Documentation/driver-api/gpio/board.rst @@ -94,6 +94,71 @@ with the help of _DSD (Device Specific Data), introduced in ACPI 5.1:: For more information about the ACPI GPIO bindings see Documentation/firmware-guide/acpi/gpio-properties.rst. +Software Nodes +-------------- + +Software nodes allow board-specific code to construct an in-memory, +device-tree-like structure using struct software_node and struct +property_entry. This structure can then be associated with a platform device, +allowing drivers to use the standard device properties API to query +configuration, just as they would on an ACPI or device tree system. + +Software-node-backed GPIOs are described using the ``PROPERTY_ENTRY_GPIO()`` +macro, which ties a software node representing the GPIO controller with +consumer device. It allows consumers to use regular gpiolib APIs, such as +gpiod_get(), gpiod_get_optional(). + +The software node representing a GPIO controller need not be attached to the +GPIO controller device. The only requirement is that the node must be +registered and its name must match the GPIO controller's label. + +For example, here is how to describe a single GPIO-connected LED. This is an +alternative to using platform_data on legacy systems. + +.. code-block:: c + + #include <linux/property.h> + #include <linux/gpio/machine.h> + #include <linux/gpio/property.h> + + /* + * 1. Define a node for the GPIO controller. Its .name must match the + * controller's label. + */ + static const struct software_node gpio_controller_node = { + .name = "gpio-foo", + }; + + /* 2. Define the properties for the LED device. */ + static const struct property_entry led_device_props[] = { + PROPERTY_ENTRY_STRING("label", "myboard:green:status"), + PROPERTY_ENTRY_STRING("linux,default-trigger", "heartbeat"), + PROPERTY_ENTRY_GPIO("gpios", &gpio_controller_node, 42, GPIO_ACTIVE_HIGH), + { } + }; + + /* 3. Define the software node for the LED device. */ + static const struct software_node led_device_swnode = { + .name = "status-led", + .properties = led_device_props, + }; + + /* + * 4. Register the software nodes and the platform device. + */ + const struct software_node *swnodes[] = { + &gpio_controller_node, + &led_device_swnode, + NULL + }; + software_node_register_node_group(swnodes); + + // Then register a platform_device for "leds-gpio" and associate + // it with &led_device_swnode via .fwnode. + +For a complete guide on converting board files to use software nodes, see +Documentation/driver-api/gpio/legacy-boards.rst. + Platform Data ------------- Finally, GPIOs can be bound to devices and functions using platform data. Board diff --git a/Documentation/driver-api/gpio/index.rst b/Documentation/driver-api/gpio/index.rst index 43f6a3afe10b..87929840e85a 100644 --- a/Documentation/driver-api/gpio/index.rst +++ b/Documentation/driver-api/gpio/index.rst @@ -12,6 +12,7 @@ Contents: driver consumer board + legacy-boards drivers-on-gpio bt8xxgpio diff --git a/Documentation/driver-api/gpio/legacy-boards.rst b/Documentation/driver-api/gpio/legacy-boards.rst new file mode 100644 index 000000000000..46e3a26dba77 --- /dev/null +++ b/Documentation/driver-api/gpio/legacy-boards.rst @@ -0,0 +1,298 @@ +Supporting Legacy Boards +======================== + +Many drivers in the kernel, such as ``leds-gpio`` and ``gpio-keys``, are +migrating away from using board-specific ``platform_data`` to a unified device +properties interface. This interface allows drivers to be simpler and more +generic, as they can query properties in a standardized way. + +On modern systems, these properties are provided via device tree. However, some +older platforms have not been converted to device tree and instead rely on +board files to describe their hardware configuration. To bridge this gap and +allow these legacy boards to work with modern, generic drivers, the kernel +provides a mechanism called **software nodes**. + +This document provides a guide on how to convert a legacy board file from using +``platform_data`` and ``gpiod_lookup_table`` to the modern software node +approach for describing GPIO-connected devices. + +The Core Idea: Software Nodes +----------------------------- + +Software nodes allow board-specific code to construct an in-memory, +device-tree-like structure using struct software_node and struct +property_entry. This structure can then be associated with a platform device, +allowing drivers to use the standard device properties API (e.g., +device_property_read_u32(), device_property_read_string()) to query +configuration, just as they would on an ACPI or device tree system. + +The gpiolib code has support for handling software nodes, so that if GPIO is +described properly, as detailed in the section below, then regular gpiolib APIs, +such as gpiod_get(), gpiod_get_optional(), and others will work. + +Requirements for GPIO Properties +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +When using software nodes to describe GPIO connections, the following +requirements must be met for the GPIO core to correctly resolve the reference: + +1. **The GPIO controller's software node "name" must match the controller's + "label".** The gpiolib core uses this name to find the corresponding + struct gpio_chip at runtime. + This software node has to be registered, but need not be attached to the + device representing the GPIO controller that is providing the GPIO in + question. It may be left as a "free floating" node. + +2. **The GPIO property must be a reference.** The ``PROPERTY_ENTRY_GPIO()`` + macro handles this as it is an alias for ``PROPERTY_ENTRY_REF()``. + +3. **The reference must have exactly two arguments:** + + - The first argument is the GPIO offset within the controller. + - The second argument is the flags for the GPIO line (e.g., + GPIO_ACTIVE_HIGH, GPIO_ACTIVE_LOW). + +The ``PROPERTY_ENTRY_GPIO()`` macro is the preferred way of defining GPIO +properties in software nodes. + +Conversion Example +------------------ + +Let's walk through an example of converting a board file that defines a GPIO- +connected LED and a button. + +Before: Using Platform Data +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +A typical legacy board file might look like this: + +.. code-block:: c + + #include <linux/platform_device.h> + #include <linux/leds.h> + #include <linux/gpio_keys.h> + #include <linux/gpio/machine.h> + + #define MYBOARD_GPIO_CONTROLLER "gpio-foo" + + /* LED setup */ + static const struct gpio_led myboard_leds[] = { + { + .name = "myboard:green:status", + .default_trigger = "heartbeat", + }, + }; + + static const struct gpio_led_platform_data myboard_leds_pdata = { + .num_leds = ARRAY_SIZE(myboard_leds), + .leds = myboard_leds, + }; + + static struct gpiod_lookup_table myboard_leds_gpios = { + .dev_id = "leds-gpio", + .table = { + GPIO_LOOKUP_IDX(MYBOARD_GPIO_CONTROLLER, 42, NULL, 0, GPIO_ACTIVE_HIGH), + { }, + }, + }; + + /* Button setup */ + static struct gpio_keys_button myboard_buttons[] = { + { + .code = KEY_WPS_BUTTON, + .desc = "WPS Button", + .active_low = 1, + }, + }; + + static const struct gpio_keys_platform_data myboard_buttons_pdata = { + .buttons = myboard_buttons, + .nbuttons = ARRAY_SIZE(myboard_buttons), + }; + + static struct gpiod_lookup_table myboard_buttons_gpios = { + .dev_id = "gpio-keys", + .table = { + GPIO_LOOKUP_IDX(MYBOARD_GPIO_CONTROLLER, 15, NULL, 0, GPIO_ACTIVE_LOW), + { }, + }, + }; + + /* Device registration */ + static int __init myboard_init(void) + { + gpiod_add_lookup_table(&myboard_leds_gpios); + gpiod_add_lookup_table(&myboard_buttons_gpios); + + platform_device_register_data(NULL, "leds-gpio", -1, + &myboard_leds_pdata, sizeof(myboard_leds_pdata)); + platform_device_register_data(NULL, "gpio-keys", -1, + &myboard_buttons_pdata, sizeof(myboard_buttons_pdata)); + + return 0; + } + +After: Using Software Nodes +~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Here is how the same configuration can be expressed using software nodes. + +Step 1: Define the GPIO Controller Node +*************************************** + +First, define a software node that represents the GPIO controller that the +LEDs and buttons are connected to. The ``name`` of this node must match the +name of the driver for the GPIO controller (e.g., "gpio-foo"). + +.. code-block:: c + + #include <linux/property.h> + #include <linux/gpio/property.h> + + #define MYBOARD_GPIO_CONTROLLER "gpio-foo" + + static const struct software_node myboard_gpio_controller_node = { + .name = MYBOARD_GPIO_CONTROLLER, + }; + +Step 2: Define Consumer Device Nodes and Properties +*************************************************** + +Next, define the software nodes for the consumer devices (the LEDs and buttons). +This involves creating a parent node for each device type and child nodes for +each individual LED or button. + +.. code-block:: c + + /* LED setup */ + static const struct software_node myboard_leds_node = { + .name = "myboard-leds", + }; + + static const struct property_entry myboard_status_led_props[] = { + PROPERTY_ENTRY_STRING("label", "myboard:green:status"), + PROPERTY_ENTRY_STRING("linux,default-trigger", "heartbeat"), + PROPERTY_ENTRY_GPIO("gpios", &myboard_gpio_controller_node, 42, GPIO_ACTIVE_HIGH), + { } + }; + + static const struct software_node myboard_status_led_swnode = { + .name = "status-led", + .parent = &myboard_leds_node, + .properties = myboard_status_led_props, + }; + + /* Button setup */ + static const struct software_node myboard_keys_node = { + .name = "myboard-keys", + }; + + static const struct property_entry myboard_wps_button_props[] = { + PROPERTY_ENTRY_STRING("label", "WPS Button"), + PROPERTY_ENTRY_U32("linux,code", KEY_WPS_BUTTON), + PROPERTY_ENTRY_GPIO("gpios", &myboard_gpio_controller_node, 15, GPIO_ACTIVE_LOW), + { } + }; + + static const struct software_node myboard_wps_button_swnode = { + .name = "wps-button", + .parent = &myboard_keys_node, + .properties = myboard_wps_button_props, + }; + + + +Step 3: Group and Register the Nodes +************************************ + +For maintainability, it is often beneficial to group all software nodes into a +single array and register them with one call. + +.. code-block:: c + + static const struct software_node * const myboard_swnodes[] = { + &myboard_gpio_controller_node, + &myboard_leds_node, + &myboard_status_led_swnode, + &myboard_keys_node, + &myboard_wps_button_swnode, + NULL + }; + + static int __init myboard_init(void) + { + int error; + + error = software_node_register_node_group(myboard_swnodes); + if (error) { + pr_err("Failed to register software nodes: %d\n", error); + return error; + } + + // ... platform device registration follows + } + +.. note:: + When splitting registration of nodes by devices that they represent, it is + essential that the software node representing the GPIO controller itself + is registered first, before any of the nodes that reference it. + +Step 4: Register Platform Devices with Software Nodes +***************************************************** + +Finally, register the platform devices and associate them with their respective +software nodes using the ``fwnode`` field in struct platform_device_info. + +.. code-block:: c + + static struct platform_device *leds_pdev; + static struct platform_device *keys_pdev; + + static int __init myboard_init(void) + { + struct platform_device_info pdev_info; + int error; + + error = software_node_register_node_group(myboard_swnodes); + if (error) + return error; + + memset(&pdev_info, 0, sizeof(pdev_info)); + pdev_info.name = "leds-gpio"; + pdev_info.id = PLATFORM_DEVID_NONE; + pdev_info.fwnode = software_node_fwnode(&myboard_leds_node); + leds_pdev = platform_device_register_full(&pdev_info); + if (IS_ERR(leds_pdev)) { + error = PTR_ERR(leds_pdev); + goto err_unregister_nodes; + } + + memset(&pdev_info, 0, sizeof(pdev_info)); + pdev_info.name = "gpio-keys"; + pdev_info.id = PLATFORM_DEVID_NONE; + pdev_info.fwnode = software_node_fwnode(&myboard_keys_node); + keys_pdev = platform_device_register_full(&pdev_info); + if (IS_ERR(keys_pdev)) { + error = PTR_ERR(keys_pdev); + platform_device_unregister(leds_pdev); + goto err_unregister_nodes; + } + + return 0; + + err_unregister_nodes: + software_node_unregister_node_group(myboard_swnodes); + return error; + } + + static void __exit myboard_exit(void) + { + platform_device_unregister(keys_pdev); + platform_device_unregister(leds_pdev); + software_node_unregister_node_group(myboard_swnodes); + } + +With these changes, the generic ``leds-gpio`` and ``gpio-keys`` drivers will +be able to probe successfully and get their configuration from the properties +defined in the software nodes, removing the need for board-specific platform +data. diff --git a/Documentation/driver-api/pin-control.rst b/Documentation/driver-api/pin-control.rst index 27ea1236307e..8208924e513e 100644 --- a/Documentation/driver-api/pin-control.rst +++ b/Documentation/driver-api/pin-control.rst @@ -863,7 +863,7 @@ has to be handled by the ``<linux/gpio/consumer.h>`` interface. Instead view thi a certain pin config setting. Look in e.g. ``<linux/pinctrl/pinconf-generic.h>`` and you find this in the documentation: - PIN_CONFIG_OUTPUT: + PIN_CONFIG_LEVEL: this will configure the pin in output, use argument 1 to indicate high level, argument 0 to indicate low level. @@ -897,7 +897,7 @@ And your machine configuration may look like this: }; static unsigned long uart_sleep_mode[] = { - PIN_CONF_PACKED(PIN_CONFIG_OUTPUT, 0), + PIN_CONF_PACKED(PIN_CONFIG_LEVEL, 0), }; static struct pinctrl_map pinmap[] __initdata = { |