[PATCH v9 0/4] gpio-sim: configfs-based GPIO simulator

From: Bartosz Golaszewski
Date: Thu Nov 18 2021 - 09:52:01 EST

This is another shot at the gpio-sim testing module. As there was no
reasoning with configfs maintainers for many months, this time the whole
concept of committable items has been dropped. Instead, each configfs
chip item (or rather a group - more on that later) exposes a new
attribute called 'live'. Writing 1 to it brings the chip on-line
(registers the platform device) and writing 0 tears it down.

There are some caveats to that approach - for example: we can't block
the user-space from deleting chip items when chips are live but is just
handled by silently destroying the chip device in the background.

Andy (rightfully) pointed out that parsing of the lists of line names is
awkward so in this iteration it's been replaced by a system that is more
elegant and will allow to easily extend configuration options for
specific GPIO lines. This is achieved by turning the chip's configfs
item into a configfs group and allowing the user-space to create
additional items inside it. The items must be called line<offset> (e.g.
line0, line12 etc.) where the offset part indicates to the module the
offset for which given item stores the configuration for. Within each
such line item, there are additional attributes that allow specifying
configuration for specific lines. Currently we only support the 'name'
attribute but I plan to extend that to support GPIO hogging too.

v1 -> v2:
- add selftests for gpio-sim
- add helper programs for selftests
- update the configfs rename callback to work with the new API introduced in
- fix a missing quote in the documentation
- use !! whenever using bits operation that are required to return 0 or 1
- use provided bitmap API instead of reimplementing copy or fill operations
- fix a deadlock in gpio_sim_direction_output()
- add new read-only configfs attributes for mapping of configfs items to GPIO
device names
- and address other minor issues pointed out in reviews of v1

v2 -> v3:
- use devm_bitmap_alloc() instead of the zalloc variant if we're initializing
the bitmap with 1s
- drop the patch exporting device_is_bound()
- don't return -ENODEV from dev_nam and chip_name configfs attributes, return
a string indicating that the device is not available yet ('n/a')
- fix indentation where it makes sense
- don't protect IDA functions which use their own locking and where it's not
- use kmemdup() instead of kzalloc() + memcpy()
- collected review tags
- minor coding style fixes

v3 -> v4:
- return 'none' instead of 'n/a' from dev_name and chip_name before the device
is registered
- use sysfs_emit() instead of s*printf()
- drop GPIO_SIM_MAX_PROP as it's only used in an array's definition where it's
fine to hardcode the value

v4 -> v5:
- drop lib patches that are already upstream
- use BIT() instead of (1UL << bit) for flags
- fix refcounting for the configfs_dirent in rename()
- drop d_move() from the rename() callback
- free memory allocated for the live and pending groups in configfs_d_iput()
and not in detach_groups()
- make sure that if a group of some name is in the live directory, a new group
with the same name cannot be created in the pending directory

v5 -> v6:
- go back to using (1UL << bit) instead of BIT()
- if the live group dentry doesn't exist for whatever reason at the time when
mkdir() in the pending group is called (would be a BUG()), return -ENOENT
instead of -EEXIST which should only be returned if given subsystem already
exists in either live or pending group

v6 -> v7:
- as detailed by Andy in commit 6fda593f3082 ("gpio: mockup: Convert to use
software nodes") removing device properties after the platform device is
removed but before the GPIO device gets dropped can lead to a use-after-free
bug - use software nodes to manually control the freeing of the properties

v7 -> v8:
- fixed some minor coding style issues as pointed out by Andy

v8 -> v9:
- dropped the patches implementing committable-items and reworked the
driver to not use them
- reworked the gpio-line-names property and configuring specific lines
in general
- many smaller tweaks here and there

Bartosz Golaszewski (4):
gpio: sim: new testing module
selftests: gpio: provide a helper for reading chip info
selftests: gpio: add a helper for reading GPIO line names
selftests: gpio: add test cases for gpio-sim

Documentation/admin-guide/gpio/gpio-sim.rst | 67 ++
drivers/gpio/Kconfig | 8 +
drivers/gpio/Makefile | 1 +
drivers/gpio/gpio-sim.c | 990 ++++++++++++++++++
tools/testing/selftests/gpio/.gitignore | 2 +
tools/testing/selftests/gpio/Makefile | 4 +-
tools/testing/selftests/gpio/config | 1 +
tools/testing/selftests/gpio/gpio-chip-info.c | 57 +
tools/testing/selftests/gpio/gpio-line-name.c | 55 +
tools/testing/selftests/gpio/gpio-sim.sh | 266 +++++
10 files changed, 1449 insertions(+), 2 deletions(-)
create mode 100644 Documentation/admin-guide/gpio/gpio-sim.rst
create mode 100644 drivers/gpio/gpio-sim.c
create mode 100644 tools/testing/selftests/gpio/gpio-chip-info.c
create mode 100644 tools/testing/selftests/gpio/gpio-line-name.c
create mode 100755 tools/testing/selftests/gpio/gpio-sim.sh