Documentation: gpio: Reconfiguration with unset direction (uAPI v2)

Update description of reconfiguration rules, adding requirement that a
direction flag be set to enable changing configuration for

Documentation: gpio: Reconfiguration with unset direction (uAPI v2)

Update description of reconfiguration rules, adding requirement that a
direction flag be set to enable changing configuration for a line.

Signed-off-by: Kent Gibson <warthog618@gmail.com>
Link: https://lore.kernel.org/r/20240626052925.174272-5-warthog618@gmail.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

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Documentation: gpio: Reconfiguration with unset direction (uAPI v1)

Update description of reconfiguration rules, adding requirement that a
direction flag be set or the configuration is considered in

Documentation: gpio: Reconfiguration with unset direction (uAPI v1)

Update description of reconfiguration rules, adding requirement that a
direction flag be set or the configuration is considered invalid.

Signed-off-by: Kent Gibson <warthog618@gmail.com>
Link: https://lore.kernel.org/r/20240626052925.174272-4-warthog618@gmail.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

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Documentation: gpio: Clarify effect of active low flag on line edges

The documentation does not make sufficiently clear that edge polarity is
based on changes to the logical line values, and that th

Documentation: gpio: Clarify effect of active low flag on line edges

The documentation does not make sufficiently clear that edge polarity is
based on changes to the logical line values, and that the physical
polarity of edges is dependent on the active low flag.

Clarify the relationship between the active low flag and edge polarity
for the functions that read edge events.

Suggested-by: David C. Rankin <drankinatty@gmail.com>
Signed-off-by: Kent Gibson <warthog618@gmail.com>
Link: https://lore.kernel.org/r/20240610092157.9147-3-warthog618@gmail.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

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Documentation: gpio: Clarify effect of active low flag on line values

The documentation does not make sufficiently clear that the uAPI deals with
logical line values, nor does it describe the influe

Documentation: gpio: Clarify effect of active low flag on line values

The documentation does not make sufficiently clear that the uAPI deals with
logical line values, nor does it describe the influence of the active low
flag on the mapping between physical and logical line values.

Clarify the relationship between physical and logical line values and the
effect of the active low flag for ioctls passing line values.

Suggested-by: David C. Rankin <drankinatty@gmail.com>
Signed-off-by: Kent Gibson <warthog618@gmail.com>
Link: https://lore.kernel.org/r/20240610092157.9147-2-warthog618@gmail.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

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docs: gpio: prefer pread(2) for interrupt reading

In legacy sysfs GPIO, when using poll(2) on the sysfs GPIO value for
state change awaiting, a subsequent read(2) is required for consuming
the event

docs: gpio: prefer pread(2) for interrupt reading

In legacy sysfs GPIO, when using poll(2) on the sysfs GPIO value for
state change awaiting, a subsequent read(2) is required for consuming
the event, which the doc recommends the use of lseek(2) or
close-and-reopen to reset the file offset afterwards.

The recommendations however, require at least 2 syscalls to consume
the event. Gladly, use of pread(2) require only 1 syscall for the
consumption. Let's advertise this usage by prioritizing its placement.

Signed-off-by: Huichun Feng <foxhoundsk.tw@gmail.com>
Link: https://lore.kernel.org/r/20240609173728.2950808-1-foxhoundsk.tw@gmail.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

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