[PATCH v2 00/10] Introduce configfs-based interface for gpio-aggregator

[Koichiro Den <koichiro.den@xxxxxxxxxxxxx>]

This patch series introduces a configfs-based interface to gpio-aggregator
to address limitations in the existing 'new_device' interface.

The existing 'new_device' interface has several limitations:

  #1. No way to determine when GPIO aggregator creation is complete.
  #2. No way to retrieve errors when creating a GPIO aggregator.
  #3. No way to trace a GPIO line of an aggregator back to its
      corresponding physical device.
  #4. The 'new_device' echo does not indicate which virtual gpiochip<N>
      was created.
  #5. No way to assign names to GPIO lines exported through an aggregator.

Although Issue#1 to #3 could technically be resolved easily without
configfs, using configfs offers a streamlined, modern, and extensible
approach, especially since gpio-sim and gpio-virtuser already utilize
configfs.

This v2 patch series includes 10 patches:

  Patch#1:   Preparation for Patch#2.
  Patch#2:   Introduce minimal configfs interface.
             Addresses Issue#1 to Issue#3.
  Patch#3:   Addresses Issue#4.
  Patch#4:   Preparation for Patch#5.
  Patch#5:   Addresses Issue#5.
  Patch#6-7: Prepare for Patch#8.
  Patch#8:   Expose devices create with sysfs to configfs.
  Patch#9:   Suppress deferred probe for purely configfs-based aggregators.
  Patch#10:  Documentation.

Changes for v2:
  - Addressed feedback from Bartosz:
    * Expose devices created with sysfs to configfs.
    * Drop 'num_lines' attribute.
    * Fix bugs and crashes.
    * Organize internal symbol prefixes more cleanly.
  - Split diffs for improved reviewability.
  - Update kernel doc to reflect the changes.

RFC (v1): https://lore.kernel.org/linux-gpio/20250129155525.663780-1-koichiro.den@xxxxxxxxxxxxx/T/#u

Koichiro Den (10):
  gpio: aggregator: reorder functions to prepare for configfs
    introduction
  gpio: aggregator: introduce basic configfs interface
  gpio: aggregator: add read-only 'dev_name' configfs attribute
  gpio: aggregator: add read-write 'name' attribute
  gpio: aggregator: expose custom line names to forwarder gpio_chip
  gpio: aggregator: rename 'name' to 'key' in aggr_parse()
  gpio: aggregator: clean up gpio_aggregator_free()
  gpio: aggregator: expoose aggregator created via legacy sysfs to
    configfs
  gpio: aggregator: cancel deferred probe for devices created via
    configfs
  Documentation: gpio: document configfs interface for gpio-aggregator

 .../admin-guide/gpio/gpio-aggregator.rst      |   93 ++
 drivers/gpio/gpio-aggregator.c                | 1194 ++++++++++++++---
 2 files changed, 1103 insertions(+), 184 deletions(-)

-- 
2.45.2