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>
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>
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>
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>
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>
Clarify that line values are logical, not physical, by replacing high/low
terminology with active/inactive.
Signed-off-by: Kent Gibson <warthog618@gmail.com>
Reviewed-by: Andy Shevchenko <amdy.shevchenko@gmail.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
The existing uAPI documentation does not adequately describe how the kernel
handles the case where the underlying hardware or driver does not support
the requested configuration.
Add a Configuration Support section describing that behaviour to both the
v1 and v2 documentation, and better document the errors returned where the
requested configuration cannot be supported.
Signed-off-by: Kent Gibson <warthog618@gmail.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Add documentation for v1 of the GPIO character device userspace API
to the obsolete section of both the admin-guide and userspace-api
books.
Signed-off-by: Kent Gibson <warthog618@gmail.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Update GPIO sysfs interface documentation to reference the new
chardev document rather than gpio.h.
Signed-off-by: Kent Gibson <warthog618@gmail.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
The GPIO sysfs API is long obsolete, so highlight this even further
by moving it into an obsolete APIs section in both the admin-guide
and userspace-api books.
Signed-off-by: Kent Gibson <warthog618@gmail.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Add documentation for the GPIO character device userspace API.
Added to the userspace-api book, but also provide a link from the
admin-guide book, as historically the GPIO documentation has been
there.
Signed-off-by: Kent Gibson <warthog618@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
