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130 lines
4.5 KiB
Diff
130 lines
4.5 KiB
Diff
From 6a205b4070ad6e129f80087d02baf0c7afd4b7e1 Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Jean-Fran=C3=A7ois=20Lessard?= <jefflessard3@gmail.com>
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Date: Sun, 31 Aug 2025 00:23:51 -0400
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Subject: [PATCH 44/54] TEST: docs: ABI: auxdisplay: document linedisp library
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sysfs attributes
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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Add ABI documentation for sysfs attributes provided by the line-display
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auxdisplay library module. These attributes enable text message display and
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configuration on character-based auxdisplay devices.
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Documents previously undocumented attributes:
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- message, scroll_step_ms (introduced in v5.16)
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- map_seg7, map_seg14 (introduced in v6.9)
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Documents newly added attribute:
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- num_chars (targeted for v6.18)
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The line-display library is used by multiple auxdisplay drivers and
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can expose these attributes either on linedisp.N child devices or
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directly on parent auxdisplay devices.
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Signed-off-by: Jean-François Lessard <jefflessard3@gmail.com>
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---
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.../ABI/testing/sysfs-auxdisplay-linedisp | 90 +++++++++++++++++++
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1 file changed, 90 insertions(+)
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create mode 100644 Documentation/ABI/testing/sysfs-auxdisplay-linedisp
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diff --git a/Documentation/ABI/testing/sysfs-auxdisplay-linedisp b/Documentation/ABI/testing/sysfs-auxdisplay-linedisp
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new file mode 100644
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index 000000000000..63c47f19275e
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--- /dev/null
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+++ b/Documentation/ABI/testing/sysfs-auxdisplay-linedisp
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@@ -0,0 +1,90 @@
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+What: /sys/.../message
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+Date: October 2021
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+KernelVersion: 5.16
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+Description:
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+ Controls the text message displayed on character line displays.
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+
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+ Reading returns the current message with a trailing newline.
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+ Writing updates the displayed message. Messages longer than the
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+ display width will automatically scroll. Trailing newlines in
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+ input are automatically trimmed.
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+
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+ Writing an empty string clears the display.
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+
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+ Example:
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+ echo "Hello World" > message
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+ cat message # Returns "Hello World\n"
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+
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+What: /sys/.../scroll_step_ms
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+Date: October 2021
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+KernelVersion: 5.16
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+Description:
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+ Controls the scrolling speed for messages longer than the display
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+ width, specified in milliseconds per scroll step.
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+
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+ Setting to 0 disables scrolling. Default is 500ms.
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+
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+ Example:
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+ echo "250" > scroll_step_ms # 4Hz scrolling
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+ cat scroll_step_ms # Returns "250\n"
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+
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+What: /sys/.../num_chars
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+Date: November 2025
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+KernelVersion: 6.18
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+Contact: Jean-François Lessard <jefflessard3@gmail.com>
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+Description:
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+ Read-only attribute showing the character width capacity of
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+ the line display device. Messages longer than this will scroll.
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+
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+ Example:
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+ cat num_chars # Returns "16\n" for 16-char display
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+
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+What: /sys/.../map_seg7
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+Date: January 2024
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+KernelVersion: 6.9
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+Description:
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+ Read/write binary blob representing the ASCII-to-7-segment
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+ display conversion table used by the linedisp driver, as defined
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+ by struct seg7_conversion_map in <linux/map_to_7segment.h>.
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+
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+ Only visible on displays with 7-segment capability.
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+
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+ This attribute is not human-readable. Writes must match the
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+ struct size exactly, else -EINVAL is returned; reads return the
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+ entire mapping as a binary blob.
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+
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+ This interface and its implementation match existing conventions
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+ used in segment-mapped display drivers since 2005.
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+
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+ ABI note: This style of binary sysfs attribute *is an exception*
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+ to current "one value per file, text only" sysfs rules, for
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+ historical compatibility and driver uniformity. New drivers are
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+ discouraged from introducing additional binary sysfs ABIs.
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+
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+ Reference interface guidance:
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+ - include/uapi/linux/map_to_7segment.h
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+
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+What: /sys/.../map_seg14
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+Date: January 2024
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+KernelVersion: 6.9
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+Description:
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+ Read/write binary blob representing the ASCII-to-14-segment
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+ display conversion table used by the linedisp driver, as defined
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+ by struct seg14_conversion_map in <linux/map_to_14segment.h>.
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+
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+ Only visible on displays with 14-segment capability.
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+
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+ This attribute is not human-readable. Writes must match the
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+ struct size exactly, else -EINVAL is returned; reads return the
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+ entire mapping as a binary blob.
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+
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+ This interface and its implementation match existing conventions
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+ used by segment-mapped display drivers since 2005.
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+
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+ ABI note: This style of binary sysfs attribute *is an exception*
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+ to current "one value per file, text only" sysfs rules, for
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+ historical compatibility and driver uniformity. New drivers are
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+ discouraged from introducing additional binary sysfs ABIs.
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+
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+ Reference interface guidance:
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+ - include/uapi/linux/map_to_14segment.h
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--
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2.34.1
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