xref: /linux/Documentation/ABI/testing/sysfs-auxdisplay-linedisp (revision 94e244d9ccab578f83a218ec58376d025014fcce)

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/.../num_chars
Date:		November 2025
KernelVersion:	6.18
Contact:	Jean-François Lessard <jefflessard3@gmail.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/.../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/.../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