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Date: Mon, 10 Jun 2024 17:21:57 +0800 From: Kent Gibson <warthog618@...il.com> To: linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org, linux-doc@...r.kernel.org, brgl@...ev.pl, corbet@....net, drankinatty@...il.com Cc: Kent Gibson <warthog618@...il.com> Subject: [PATCH 2/2] 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@...il.com> Signed-off-by: Kent Gibson <warthog618@...il.com> --- .../userspace-api/gpio/gpio-lineevent-data-read.rst | 5 +++++ Documentation/userspace-api/gpio/gpio-v2-line-event-read.rst | 5 +++++ 2 files changed, 10 insertions(+) diff --git a/Documentation/userspace-api/gpio/gpio-lineevent-data-read.rst b/Documentation/userspace-api/gpio/gpio-lineevent-data-read.rst index 68b8d4f9f604..d1e7e2383b0d 100644 --- a/Documentation/userspace-api/gpio/gpio-lineevent-data-read.rst +++ b/Documentation/userspace-api/gpio/gpio-lineevent-data-read.rst @@ -44,6 +44,11 @@ Edge detection must be enabled for the input line using either both. Edge events are then generated whenever edge interrupts are detected on the input line. +Edges are defined in terms of changes to the logical line value, so an inactive +to active transition is a rising edge. If ``GPIOHANDLE_REQUEST_ACTIVE_LOW`` is +set then logical polarity is the opposite of physical polarity, and +``GPIOEVENT_REQUEST_RISING_EDGE`` then corresponds to a falling physical edge. + The kernel captures and timestamps edge events as close as possible to their occurrence and stores them in a buffer from where they can be read by userspace at its convenience using `read()`. diff --git a/Documentation/userspace-api/gpio/gpio-v2-line-event-read.rst b/Documentation/userspace-api/gpio/gpio-v2-line-event-read.rst index 6513c23fb7ca..1312668e0f6a 100644 --- a/Documentation/userspace-api/gpio/gpio-v2-line-event-read.rst +++ b/Documentation/userspace-api/gpio/gpio-v2-line-event-read.rst @@ -40,6 +40,11 @@ Edge detection must be enabled for the input line using either both. Edge events are then generated whenever edge interrupts are detected on the input line. +Edges are defined in terms of changes to the logical line value, so an inactive +to active transition is a rising edge. If ``GPIO_V2_LINE_FLAG_ACTIVE_LOW`` is +set then logical polarity is the opposite of physical polarity, and +``GPIO_V2_LINE_FLAG_EDGE_RISING`` then corresponds to a falling physical edge. + The kernel captures and timestamps edge events as close as possible to their occurrence and stores them in a buffer from where they can be read by userspace at its convenience using `read()`. -- 2.39.2
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