2. Marvell CNXK GPIO Driver

CNXK GPIO PMD configures and manages GPIOs available on the system using standard enqueue/dequeue mechanism offered by raw device abstraction. PMD relies both on standard sysfs GPIO interface provided by the Linux kernel and GPIO kernel driver custom interface allowing one to install userspace interrupt handlers.

2.1. Features

Following features are available:

export/unexport a GPIO
read/write specific value from/to exported GPIO
set GPIO direction
set GPIO edge that triggers interrupt
set GPIO active low
register interrupt handler for specific GPIO
multiprocess aware

2.2. Requirements

PMD relies on modified kernel GPIO driver which exposes ioctl() interface for installing interrupt handlers for low latency signal processing.

Driver is shipped with Marvell SDK.

2.3. Limitations

In multiprocess mode, user-space application must ensure no GPIO sharing across processes takes place.

2.4. Device Setup

CNXK GPIO PMD binds to virtual device which gets created by passing –vdev=cnxk_gpio,gpiochip=<number> command line to EAL. gpiochip parameter tells PMD which GPIO controller should be used. Available controllers are available under /sys/class/gpio. For further details on how Linux represents GPIOs in userspace please refer to sysfs.txt.

If gpiochip=<number> was omitted then first gpiochip from the alphabetically sort list of available gpiochips is used.

$ ls /sys/class/gpio
export gpiochip448 unexport

In above scenario only one GPIO controller is present hence –vdev=cnxk_gpio,gpiochip=448 should be passed to EAL.

Before performing actual data transfer one needs to call rte_rawdev_queue_count() followed by rte_rawdev_queue_conf_get(). The former returns number GPIOs available in the system irrespective of GPIOs being controllable or not. Thus it is user responsibility to pick the proper ones. The latter call simply returns queue capacity.

In order to allow using only subset of available GPIOs allowlist PMD param may be used. For example passing –vdev=cnxk_gpio,gpiochip=448,allowlist=[0,1,2,3] to EAL will deny using all GPIOs except those specified explicitly in the allowlist.

Respective queue needs to be configured with rte_rawdev_queue_setup(). This call barely exports GPIO to userspace.

To perform actual data transfer use standard rte_rawdev_enqueue_buffers() and rte_rawdev_dequeue_buffers() APIs. Not all messages produce sensible responses hence dequeueing is not always necessary.

2.5. CNXK GPIO PMD

PMD accepts struct cnxk_gpio_msg messages which differ by type and payload. Message types along with description are listed below. As for the usage examples please refer to cnxk_gpio_selftest(). There’s a set of convenient wrappers available, one for each existing command.

2.5.1. Set GPIO value

Message is used to set output to low or high. This does not work for GPIOs configured as input.

Message must have type set to CNXK_GPIO_MSG_TYPE_SET_PIN_VALUE.

Payload must be an integer set to 0 (low) or 1 (high).

Consider using rte_pmd_gpio_set_pin_value() wrapper.

2.5.2. Set GPIO edge

Message is used to set edge that triggers interrupt.

Message must have type set to CNXK_GPIO_MSG_TYPE_SET_PIN_EDGE.

Payload must be enum cnxk_gpio_pin_edge.

Consider using rte_pmd_gpio_set_pin_edge() wrapper.

2.5.3. Set GPIO direction

Message is used to change GPIO direction to either input or output.

Message must have type set to CNXK_GPIO_MSG_TYPE_SET_PIN_DIR.

Payload must be enum cnxk_gpio_pin_dir.

Consider using rte_pmd_gpio_set_pin_dir() wrapper.

2.5.4. Set GPIO active low

Message is used to set whether pin is active low.

Message must have type set to CNXK_GPIO_MSG_TYPE_SET_PIN_ACTIVE_LOW.

Payload must be an integer set to 0 or 1. The latter activates inversion.

Consider using rte_pmd_gpio_set_pin_active_low() wrapper.

2.5.5. Get GPIO value

Message is used to read GPIO value. Value can be 0 (low) or 1 (high).

Message must have type set to CNXK_GPIO_MSG_TYPE_GET_PIN_VALUE.

Payload contains integer set to either 0 or 1.

Consider using rte_pmd_gpio_get_pin_value() wrapper.

2.5.6. Get GPIO edge

Message is used to read GPIO edge.

Message must have type set to CNXK_GPIO_MSG_TYPE_GET_PIN_EDGE.

Payload contains enum cnxk_gpio_pin_edge.

Consider using rte_pmd_gpio_get_pin_edge() wrapper.

2.5.7. Get GPIO direction

Message is used to read GPIO direction.

Message must have type set to CNXK_GPIO_MSG_TYPE_GET_PIN_DIR.

Payload contains enum cnxk_gpio_pin_dir.

Consider using rte_pmd_gpio_get_pin_dir() wrapper.

2.5.8. Get GPIO active low

Message is used check whether inverted logic is active.

Message must have type set to CNXK_GPIO_MSG_TYPE_GET_PIN_ACTIVE_LOW.

Payload contains an integer set to 0 or 1. The latter means inverted logic is turned on.

Consider using rte_pmd_gpio_get_pin_active_low() wrapper.

2.5.9. Request interrupt

Message is used to install custom interrupt handler.

Message must have type set to CNXK_GPIO_MSG_TYPE_REGISTER_IRQ.

Payload needs to be set to struct cnxk_gpio_irq which describes interrupt being requested.

Consider using rte_pmd_gpio_register_gpio() wrapper.

2.5.10. Free interrupt

Message is used to remove installed interrupt handler.

Message must have type set to CNXK_GPIO_MSG_TYPE_UNREGISTER_IRQ.

Consider using rte_pmd_gpio_unregister_gpio() wrapper.

2.6. Self test

On EAL initialization CNXK GPIO device will be probed and populated into the list of raw devices on condition --vdev=cnxk_gpio,gpiochip=<number> was passed. rte_rawdev_get_dev_id("CNXK_GPIO") returns unique device id. Use this identifier for further rawdev function calls.

Selftest rawdev API can be used to verify the PMD functionality. Note it blindly assumes that all GPIOs are controllable so some errors during test are expected.