diff options
| author | Bartosz Golaszewski <bartosz.golaszewski@linaro.org> | 2025-04-01 14:46:45 +0200 |
|---|---|---|
| committer | Bartosz Golaszewski <bartosz.golaszewski@linaro.org> | 2025-04-08 10:41:59 +0200 |
| commit | 2de1cf175c00927c286f8bd72e18602fe072af95 (patch) | |
| tree | baa38a3c0aa6f2d536dfb27ea9737fce5b9ddd63 | |
| parent | 3af64f175b2405270bd0926153d9856a49b58352 (diff) | |
gpio: TODO: track the removal of regulator-related workarounds
The GPIOD_FLAGS_BIT_NONEXCLUSIVE flag and devm_gpiod_unhinge() function
should be replaced with a better solution. The pwrseq subsystem is a good
candidate. GPIOs themselves should remain a unique resource. Add a task
for tracking the removal of these deprecated symbols.
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20250401-gpio-todo-remove-nonexclusive-v2-4-7c1380797b0d@linaro.org
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
| -rw-r--r-- | drivers/gpio/TODO | 34 |
1 files changed, 34 insertions, 0 deletions
diff --git a/drivers/gpio/TODO b/drivers/gpio/TODO index b5f0a7a2e1bf..4b70cbaa1caa 100644 --- a/drivers/gpio/TODO +++ b/drivers/gpio/TODO @@ -186,3 +186,37 @@ their hardware offsets within the chip. Encourage users to switch to using them and eventually remove the existing global export/unexport attribues. + +------------------------------------------------------------------------------- + +Remove GPIOD_FLAGS_BIT_NONEXCLUSIVE + +GPIOs in the linux kernel are meant to be an exclusive resource. This means +that the GPIO descriptors (the software representation of the hardware concept) +are not reference counted and - in general - only one user at a time can +request a GPIO line and control its settings. The consumer API is designed +around full control of the line's state as evidenced by the fact that, for +instance, gpiod_set_value() does indeed drive the line as requested, instead +of bumping an enable counter of some sort. + +A problematic use-case for GPIOs is when two consumers want to use the same +descriptor independently. An example of such a user is the regulator subsystem +which may instantiate several struct regulator_dev instances containing +a struct device but using the same enable GPIO line. + +A workaround was introduced in the form of the GPIOD_FLAGS_BIT_NONEXCLUSIVE +flag but its implementation is problematic: it does not provide any +synchronization of usage nor did it introduce any enable count meaning the +non-exclusive users of the same descriptor will in fact "fight" for the +control over it. This flag should be removed and replaced with a better +solution, possibly based on the new power sequencing subsystem. + +------------------------------------------------------------------------------- + +Remove devm_gpiod_unhinge() + +devm_gpiod_unhinge() is provided as a way to transfer the ownership of managed +enable GPIOs to the regulator core. Rather than doing that however, we should +make it possible for the regulator subsystem to deal with GPIO resources the +lifetime of which it doesn't control as logically, a GPIO obtained by a caller +should also be freed by it. |