[PATCH v5 0/5] gpiolib: cdev: relocate debounce_period_us

Kent Gibson
2023-12-19T00:42:16Z

This series contains minor improvements to gpiolib-cdev.

The banner change is relocating the debounce_period_us from gpiolib's
struct gpio_desc to cdev's struct line. Patch 1 stores the field
locally in cdev. Patch 2 removes the now unused field from gpiolib.

Patch 3 is somewhat related and removes a FIXME from
gpio_desc_to_lineinfo(). The FIXME relates to a race condition in
the calculation of the used flag, but I would assert that from
the userspace perspective the read operation itself is inherently racy.
The line being reported as unused in the info provides no guarantee -
it just an indicator that requesting the line is likely to succeed -
assuming the line is not otherwise requested in the meantime.
Given the overall operation is racy, trying to stamp out an unlikely
race within the operation is pointless. Accept it as a possibility
that has negligible side-effects and reduce the number of locks held
simultaneously and the duration that the gpio_lock is held.

Patches 1 and 3 introduce usage of guard() and scoped_guard() to cdev.
Patch 4 replaces any remaining discrete lock/unlock calls around
critical sections with guard() or scoped_guard().

Patch 5 is unrelated to debounce or info, but addresses Andy's
recent lamentation that the linereq get/set values functions are
confusing and under documented.
Figured I may as well add that while I was in there.

Changes v4 -> v5:
(all changes are to patch 1)
- rename line_is_supplemental() to line_has_supinfo().
- document line_set_debounce_period().

Changes v3 -> v4:
(changes other than using --histogram are to patch 1)
- use --histogram to generate patches.
- include cleanup.h.
- make supinfo_lock static.
- immediately return from supinfo_to_lineinfo() if line not found.

Changes v2 -> v3:
- reorder patches to move full adoption of guard()/scoped_guard() to
patch 4.
- use guard() rather than scoped_guard() where the scope extends to the
end of the function.
- split supinfo into supinfo_tree and supinfo_lock (patch 1).
- rename flags to dflags in gpio_desc_to_lineinfo() (patch 3).

Changes v1 -> v2:
(changes are to patch 2 unless otherwise noted)
- adopt scoped_guard() for critical sections, inserting patch 1 and
updating patch 2 and 4.
- move rb_node field to beginning of struct line.
- merge struct supinfo into supinfo var declaration.
- move rb_tree field to beginning of struct supinfo.
- replace pr_warn() with WARN().
- drop explicit int to bool conversion in line_is_supplemental().
- use continue to bypass cleanup in linereq_free().
- fix typo in commit message (patch 4)

Kent Gibson (5):
gpiolib: cdev: relocate debounce_period_us from struct gpio_desc
gpiolib: remove debounce_period_us from struct gpio_desc
gpiolib: cdev: reduce locking in gpio_desc_to_lineinfo()
gpiolib: cdev: fully adopt guard() and scoped_guard()
gpiolib: cdev: improve documentation of get/set values

drivers/gpio/gpiolib-cdev.c | 402 +++++++++++++++++++++++-------------
drivers/gpio/gpiolib.c | 3 -
drivers/gpio/gpiolib.h | 5 -
3 files changed, 256 insertions(+), 154 deletions(-)

--
2.39.2