[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Message-ID: <20250901020033.60196-6-jefflessard3@gmail.com>
Date: Sun, 31 Aug 2025 22:00:29 -0400
From: Jean-François Lessard <jefflessard3@...il.com>
To: Andy Shevchenko <andy@...nel.org>,
Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH 5/5] docs: ABI: auxdisplay: document linedisp library sysfs attributes
Add ABI documentation for sysfs attributes provided by the line-display
auxdisplay library module. These attributes enable text message display and
configuration on character-based auxdisplay devices.
Documents previously undocumented attributes:
- message, scroll_step_ms (introduced in v5.16)
- map_seg7, map_seg14 (introduced in v6.9)
Documents newly added attribute:
- num_chars (targeted for v6.18)
The line-display library is used by multiple auxdisplay drivers and
can expose these attributes either on linedisp.N child devices or
directly on parent auxdisplay devices.
Signed-off-by: Jean-François Lessard <jefflessard3@...il.com>
---
.../ABI/testing/sysfs-auxdisplay-linedisp | 90 +++++++++++++++++++
1 file changed, 90 insertions(+)
create mode 100644 Documentation/ABI/testing/sysfs-auxdisplay-linedisp
diff --git a/Documentation/ABI/testing/sysfs-auxdisplay-linedisp b/Documentation/ABI/testing/sysfs-auxdisplay-linedisp
new file mode 100644
index 000000000..63c47f192
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-auxdisplay-linedisp
@@ -0,0 +1,90 @@
+What: /sys/.../message
+Date: October 2021
+KernelVersion: 5.16
+Description:
+ Controls the text message displayed on character line displays.
+
+ Reading returns the current message with a trailing newline.
+ Writing updates the displayed message. Messages longer than the
+ display width will automatically scroll. Trailing newlines in
+ input are automatically trimmed.
+
+ Writing an empty string clears the display.
+
+ Example:
+ echo "Hello World" > message
+ cat message # Returns "Hello World\n"
+
+What: /sys/.../scroll_step_ms
+Date: October 2021
+KernelVersion: 5.16
+Description:
+ Controls the scrolling speed for messages longer than the display
+ width, specified in milliseconds per scroll step.
+
+ Setting to 0 disables scrolling. Default is 500ms.
+
+ Example:
+ echo "250" > scroll_step_ms # 4Hz scrolling
+ cat scroll_step_ms # Returns "250\n"
+
+What: /sys/.../num_chars
+Date: November 2025
+KernelVersion: 6.18
+Contact: Jean-François Lessard <jefflessard3@...il.com>
+Description:
+ Read-only attribute showing the character width capacity of
+ the line display device. Messages longer than this will scroll.
+
+ Example:
+ cat num_chars # Returns "16\n" for 16-char display
+
+What: /sys/.../map_seg7
+Date: January 2024
+KernelVersion: 6.9
+Description:
+ Read/write binary blob representing the ASCII-to-7-segment
+ display conversion table used by the linedisp driver, as defined
+ by struct seg7_conversion_map in <linux/map_to_7segment.h>.
+
+ Only visible on displays with 7-segment capability.
+
+ This attribute is not human-readable. Writes must match the
+ struct size exactly, else -EINVAL is returned; reads return the
+ entire mapping as a binary blob.
+
+ This interface and its implementation match existing conventions
+ used in segment-mapped display drivers since 2005.
+
+ ABI note: This style of binary sysfs attribute *is an exception*
+ to current "one value per file, text only" sysfs rules, for
+ historical compatibility and driver uniformity. New drivers are
+ discouraged from introducing additional binary sysfs ABIs.
+
+ Reference interface guidance:
+ - include/uapi/linux/map_to_7segment.h
+
+What: /sys/.../map_seg14
+Date: January 2024
+KernelVersion: 6.9
+Description:
+ Read/write binary blob representing the ASCII-to-14-segment
+ display conversion table used by the linedisp driver, as defined
+ by struct seg14_conversion_map in <linux/map_to_14segment.h>.
+
+ Only visible on displays with 14-segment capability.
+
+ This attribute is not human-readable. Writes must match the
+ struct size exactly, else -EINVAL is returned; reads return the
+ entire mapping as a binary blob.
+
+ This interface and its implementation match existing conventions
+ used by segment-mapped display drivers since 2005.
+
+ ABI note: This style of binary sysfs attribute *is an exception*
+ to current "one value per file, text only" sysfs rules, for
+ historical compatibility and driver uniformity. New drivers are
+ discouraged from introducing additional binary sysfs ABIs.
+
+ Reference interface guidance:
+ - include/uapi/linux/map_to_14segment.h
--
2.43.0
Powered by blists - more mailing lists