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[184.162.17.197]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-79344899b25sm12408376d6.7.2025.09.18.05.13.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 18 Sep 2025 05:13:35 -0700 (PDT) From: =?UTF-8?q?Jean-Fran=C3=A7ois=20Lessard?= To: Andy Shevchenko , Geert Uytterhoeven Cc: linux-kernel@vger.kernel.org Subject: [PATCH v2 1/5] docs: ABI: auxdisplay: document linedisp library sysfs attributes Date: Thu, 18 Sep 2025 08:13:11 -0400 Message-ID: <20250918121321.116248-2-jefflessard3@gmail.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20250918121321.116248-1-jefflessard3@gmail.com> References: <20250918121321.116248-1-jefflessard3@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable 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) 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-Fran=C3=A7ois Lessard --- .../ABI/testing/sysfs-auxdisplay-linedisp | 79 +++++++++++++++++++ 1 file changed, 79 insertions(+) create mode 100644 Documentation/ABI/testing/sysfs-auxdisplay-linedisp diff --git a/Documentation/ABI/testing/sysfs-auxdisplay-linedisp b/Document= ation/ABI/testing/sysfs-auxdisplay-linedisp new file mode 100644 index 000000000000..45cf4e5a2feb --- /dev/null +++ b/Documentation/ABI/testing/sysfs-auxdisplay-linedisp @@ -0,0 +1,79 @@ +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/.../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 . + + 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 . + + 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 --=20 2.43.0