tree 0bbebe4a0cd6707e8ca62ec77a46758ddc213e36
parent 9890e7854236206de6be7367d4c77dffd49805ee
author Geert Uytterhoeven <geert+renesas@glider.be> 1561732450 +0200
committer Geert Uytterhoeven <geert+renesas@glider.be> 1584961762 +0100

gpio: Add GPIO Aggregator

GPIO controllers are exported to userspace using /dev/gpiochip*
character devices.  Access control to these devices is provided by
standard UNIX file system permissions, on an all-or-nothing basis:
either a GPIO controller is accessible for a user, or it is not.
Currently no mechanism exists to control access to individual GPIOs.

Hence add a GPIO driver to aggregate existing GPIOs, and expose them as
a new gpiochip.

This supports the following use cases:
  - Aggregating GPIOs using Sysfs
    This is useful for implementing access control, and assigning a set
    of GPIOs to a specific user or virtual machine.
  - Generic GPIO Driver
    This is useful for industrial control, where it can provide
    userspace access to a simple GPIO-operated device described in DT,
    cfr. e.g. spidev for SPI-operated devices.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Eugeniu Rosca <erosca@de.adit-jv.com>
Tested-by: Eugeniu Rosca <erosca@de.adit-jv.com>
---
v6:
  - Use gpiod_to_chip() instead of open-coding,
  - Drop debug print of gpio_desc.label, as it usually just points to
    the GPIO Aggregator itself,
  - Drop no longer needed #include "gpiolib.h",
  - Fix missing offset translation in gpio_fwd_set_config(),
  - Use GPIO_LOOKUP_IDX() to populate struct gpiod_lookup,

v5:
  - Add Reviewed-by, Tested-by,

v4:
  - Remove unused assignment to n in isrange(),
  - Check correct pointer after aggr->lookups->dev_id allocation,
  - Preinitialize flags to 0 in gpio_fwd_[gs]et_multiple() to avoid
    may-be-used-uninitialized warning,
  - Drop controversial GPIO repeater,
  - Update for gpiod_lookup.chip_label rename,
  - Use %pe to format error pointers,
  - Use U16_MAX instead of (u16)-1,
  - Correct comment indentation,
  - Use skip_spaces() helper,
  - Rename a and b to first_index resp. last_index,
  - Add comment to tmp[] use,
  - Improve Kconfig help text,
  - Include <linux/gpio/consumer.h> for gpiod_[gs]et_*(),
  - Drop unneeded valid_mask handling,
  - Add comment about sleeping and .set_config() support,

v3:
  - Absorb GPIO forwarder,
  - Integrate GPIO Repeater and Generic GPIO driver functionality,
  - Use the aggregator parameters to create a GPIO lookup table instead
    of an array of GPIO descriptors, which allows to simplify the code:
      1. This removes the need for calling gpio_name_to_desc(),
         gpiochip_find(), gpiochip_get_desc(), and gpiod_request(),
      2. This allows the platform device to always use
         devm_gpiod_get_index(), regardless of the origin of the GPIOs,
  - Move parameter parsing from platform device probe to sysfs attribute
    store, removing the need for platform data passing,
  - Use more devm_*() functions to simplify cleanup,
  - Add pr_fmt(),
  - General refactoring,

v2:
  - Add missing initialization of i in gpio_virt_agg_probe(),
  - Update for removed .need_valid_mask field and changed
    .init_valid_mask() signature,
  - Drop "virtual", rename to gpio-aggregator,
  - Drop bogus FIXME related to gpiod_set_transitory() expectations,
  - Use new GPIO Forwarder Helper,
  - Lift limit on the maximum number of GPIOs,
  - Improve parsing:
      - add support for specifying GPIOs by line name,
      - add support for specifying GPIO chips by ID,
      - add support for GPIO offset ranges,
      - names and offset specifiers must be separated by whitespace,
      - GPIO offsets must separated by spaces,
  - Use str_has_prefix() and kstrtouint().