Re: [PATCH v4 0/5] gpiolib: cdev: relocate debounce_period_us

[Bartosz Golaszewski]

On Sat, Dec 16, 2023 at 1:17 AM Kent Gibson <warthog618@xxxxxxxxx> wrote:
>
> 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 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 | 391 +++++++++++++++++++++++-------------
>  drivers/gpio/gpiolib.c      |   3 -
>  drivers/gpio/gpiolib.h      |   5 -
>  3 files changed, 246 insertions(+), 153 deletions(-)
>
> --
> 2.39.2
>

I just have two minor nits for patch 1/5, other than that it's ready to go.

Bart