Merge tag 'auxdisplay-for-linus-v5.16' of git://github.com/ojeda/linux

Pull auxdisplay updates from Miguel Ojeda:

 - 4-digit 7-segment and quad alphanumeric display support for the
   ht16k33 driver, allowing the user to display and scroll text
   messages, from Geert Uytterhoeven.

 - An assortment of fixes and cleanups from Geert Uytterhoeven.

 - Header cleanups from Mianhan Liu.

 - Whitespace cleanup from Huiquan Deng.

* tag 'auxdisplay-for-linus-v5.16' of git://github.com/ojeda/linux: (26 commits)
  MAINTAINERS: Add DT Bindings for Auxiliary Display Drivers
  auxdisplay: cfag12864bfb: code indent should use tabs where possible
  auxdisplay: ht16k33: remove superfluous header files
  auxdisplay: ks0108: remove superfluous header files
  auxdisplay: cfag12864bfb: remove superfluous header files
  auxdisplay: ht16k33: Make use of device properties
  auxdisplay: ht16k33: Add LED support
  dt-bindings: auxdisplay: ht16k33: Document LED subnode
  auxdisplay: ht16k33: Add support for segment displays
  auxdisplay: ht16k33: Extract frame buffer probing
  auxdisplay: ht16k33: Extract ht16k33_brightness_set()
  auxdisplay: ht16k33: Move delayed work
  auxdisplay: ht16k33: Add helper variable dev
  auxdisplay: ht16k33: Convert to simple i2c probe function
  auxdisplay: ht16k33: Remove unneeded error check in keypad probe()
  auxdisplay: ht16k33: Use HT16K33_FB_SIZE in ht16k33_initialize()
  auxdisplay: ht16k33: Fix frame buffer device blanking
  auxdisplay: ht16k33: Connect backlight to fbdev
  auxdisplay: linedisp: Add support for changing scroll rate
  auxdisplay: linedisp: Use kmemdup_nul() helper
  ...

Documentation/devicetree/bindings/auxdisplay/holtek,ht16k33.yaml

@@ -14,14 +14,21 @@ allOf:
 
 properties:
   compatible:
-    const: holtek,ht16k33
+    oneOf:
+      - items:
+          - enum:
+              - adafruit,3108  # 0.56" 4-Digit 7-Segment FeatherWing Display (Red)
+              - adafruit,3130  # 0.54" Quad Alphanumeric FeatherWing Display (Red)
+          - const: holtek,ht16k33
+
+      - const: holtek,ht16k33     # Generic 16*8 LED controller with dot-matrix display
 
   reg:
     maxItems: 1
 
   refresh-rate-hz:
     maxItems: 1
-    description: Display update interval in Hertz
+    description: Display update interval in Hertz for dot-matrix displays
 
   interrupts:
     maxItems: 1
@@ -41,10 +48,22 @@ properties:
     default: 16
     description: Initial brightness level
 
+  led:
+    type: object
+    $ref: /schemas/leds/common.yaml#
+    unevaluatedProperties: false
+
 required:
   - compatible
   - reg
-  - refresh-rate-hz
+
+if:
+  properties:
+    compatible:
+      const: holtek,ht16k33
+then:
+  required:
+    - refresh-rate-hz
 
 additionalProperties: false
 
@@ -52,6 +71,7 @@ examples:
   - |
     #include <dt-bindings/interrupt-controller/irq.h>
     #include <dt-bindings/input/input.h>
+    #include <dt-bindings/leds/common.h>
     i2c1 {
             #address-cells = <1>;
             #size-cells = <0>;
@@ -73,5 +93,11 @@ examples:
                                    <MATRIX_KEY(4, 1, KEY_F9)>,
                                    <MATRIX_KEY(5, 1, KEY_F3)>,
                                    <MATRIX_KEY(6, 1, KEY_F1)>;
+
+                    led {
+                            color = <LED_COLOR_ID_RED>;
+                            function = LED_FUNCTION_BACKLIGHT;
+                            linux,default-trigger = "backlight";
+                    };
             };
       };

MAINTAINERS

@@ -3170,6 +3170,7 @@ F:	lib/*audit.c
 AUXILIARY DISPLAY DRIVERS
 M:	Miguel Ojeda <ojeda@kernel.org>
 S:	Maintained
+F:	Documentation/devicetree/bindings/auxdisplay/
 F:	drivers/auxdisplay/
 F:	include/linux/cfag12864b.h
 

drivers/auxdisplay/Kconfig

@@ -25,6 +25,12 @@ config CHARLCD
 	  This is some character LCD core interface that multiple drivers can
 	  use.
 
+config LINEDISP
+	tristate "Character line display core support" if COMPILE_TEST
+	help
+	  This is the core support for single-line character displays, to be
+	  selected by drivers that use it.
+
 config HD44780_COMMON
 	tristate "Common functions for HD44780 (and compatibles) LCD displays" if COMPILE_TEST
 	select CHARLCD
@@ -155,6 +161,7 @@ config IMG_ASCII_LCD
 	depends on HAS_IOMEM
 	default y if MIPS_MALTA
 	select MFD_SYSCON
+	select LINEDISP
 	help
 	  Enable this to support the simple ASCII LCD displays found on
 	  development boards such as the MIPS Boston, MIPS Malta & MIPS SEAD3
@@ -162,13 +169,16 @@ config IMG_ASCII_LCD
 
 config HT16K33
 	tristate "Holtek Ht16K33 LED controller with keyscan"
-	depends on FB && OF && I2C && INPUT
+	depends on FB && I2C && INPUT
 	select FB_SYS_FOPS
 	select FB_SYS_FILLRECT
 	select FB_SYS_COPYAREA
 	select FB_SYS_IMAGEBLIT
 	select INPUT_MATRIXKMAP
 	select FB_BACKLIGHT
+	select NEW_LEDS
+	select LEDS_CLASS
+	select LINEDISP
 	help
 	  Say yes here to add support for Holtek HT16K33, RAM mapping 16*8
 	  LED controller driver with keyscan.

drivers/auxdisplay/Makefile

@@ -13,3 +13,4 @@ obj-$(CONFIG_HD44780)		+= hd44780.o
 obj-$(CONFIG_HT16K33)		+= ht16k33.o
 obj-$(CONFIG_PARPORT_PANEL)	+= panel.o
 obj-$(CONFIG_LCD2S)		+= lcd2s.o
+obj-$(CONFIG_LINEDISP)		+= line-display.o

drivers/auxdisplay/cfag12864bfb.c

@@ -12,13 +12,10 @@
 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/kernel.h>
-#include <linux/delay.h>
 #include <linux/errno.h>
 #include <linux/fb.h>
 #include <linux/mm.h>
 #include <linux/platform_device.h>
-#include <linux/string.h>
-#include <linux/uaccess.h>
 #include <linux/cfag12864b.h>
 
 #define CFAG12864BFB_NAME "cfag12864bfb"
@@ -41,8 +38,8 @@ static const struct fb_var_screeninfo cfag12864bfb_var = {
 	.yres_virtual = CFAG12864B_HEIGHT,
 	.bits_per_pixel = 1,
 	.red = { 0, 1, 0 },
-      	.green = { 0, 1, 0 },
-      	.blue = { 0, 1, 0 },
+	.green = { 0, 1, 0 },
+	.blue = { 0, 1, 0 },
 	.left_margin = 0,
 	.right_margin = 0,
 	.upper_margin = 0,
@@ -70,7 +67,7 @@ static const struct fb_ops cfag12864bfb_ops = {
 static int cfag12864bfb_probe(struct platform_device *device)
 {
 	int ret = -EINVAL;
- 	struct fb_info *info = framebuffer_alloc(0, &device->dev);
+	struct fb_info *info = framebuffer_alloc(0, &device->dev);
 
 	if (!info)
 		goto none;

drivers/auxdisplay/img-ascii-lcd.c

@@ -4,7 +4,6 @@
  * Author: Paul Burton <paul.burton@mips.com>
  */
 
-#include <generated/utsrelease.h>
 #include <linux/kernel.h>
 #include <linux/io.h>
 #include <linux/mfd/syscon.h>
@@ -14,7 +13,8 @@
 #include <linux/platform_device.h>
 #include <linux/regmap.h>
 #include <linux/slab.h>
-#include <linux/sysfs.h>
+
+#include "line-display.h"
 
 struct img_ascii_lcd_ctx;
 
@@ -27,36 +27,26 @@ struct img_ascii_lcd_ctx;
 struct img_ascii_lcd_config {
 	unsigned int num_chars;
 	bool external_regmap;
-	void (*update)(struct img_ascii_lcd_ctx *ctx);
+	void (*update)(struct linedisp *linedisp);
 };
 
 /**
  * struct img_ascii_lcd_ctx - Private data structure
- * @pdev: the ASCII LCD platform device
  * @base: the base address of the LCD registers
  * @regmap: the regmap through which LCD registers are accessed
  * @offset: the offset within regmap to the start of the LCD registers
  * @cfg: pointer to the LCD model configuration
- * @message: the full message to display or scroll on the LCD
- * @message_len: the length of the @message string
- * @scroll_pos: index of the first character of @message currently displayed
- * @scroll_rate: scroll interval in jiffies
- * @timer: timer used to implement scrolling
+ * @linedisp: line display structure
  * @curr: the string currently displayed on the LCD
  */
 struct img_ascii_lcd_ctx {
-	struct platform_device *pdev;
 	union {
 		void __iomem *base;
 		struct regmap *regmap;
 	};
 	u32 offset;
 	const struct img_ascii_lcd_config *cfg;
-	char *message;
-	unsigned int message_len;
-	unsigned int scroll_pos;
-	unsigned int scroll_rate;
-	struct timer_list timer;
+	struct linedisp linedisp;
 	char curr[] __aligned(8);
 };
 
@@ -64,8 +54,10 @@ struct img_ascii_lcd_ctx {
  * MIPS Boston development board
  */
 
-static void boston_update(struct img_ascii_lcd_ctx *ctx)
+static void boston_update(struct linedisp *linedisp)
 {
+	struct img_ascii_lcd_ctx *ctx =
+		container_of(linedisp, struct img_ascii_lcd_ctx, linedisp);
 	ulong val;
 
 #if BITS_PER_LONG == 64
@@ -90,12 +82,14 @@ static struct img_ascii_lcd_config boston_config = {
  * MIPS Malta development board
  */
 
-static void malta_update(struct img_ascii_lcd_ctx *ctx)
+static void malta_update(struct linedisp *linedisp)
 {
+	struct img_ascii_lcd_ctx *ctx =
+		container_of(linedisp, struct img_ascii_lcd_ctx, linedisp);
 	unsigned int i;
 	int err = 0;
 
-	for (i = 0; i < ctx->cfg->num_chars; i++) {
+	for (i = 0; i < linedisp->num_chars; i++) {
 		err = regmap_write(ctx->regmap,
 				   ctx->offset + (i * 8), ctx->curr[i]);
 		if (err)
@@ -173,12 +167,14 @@ static int sead3_wait_lcd_idle(struct img_ascii_lcd_ctx *ctx)
 	return 0;
 }
 
-static void sead3_update(struct img_ascii_lcd_ctx *ctx)
+static void sead3_update(struct linedisp *linedisp)
 {
+	struct img_ascii_lcd_ctx *ctx =
+		container_of(linedisp, struct img_ascii_lcd_ctx, linedisp);
 	unsigned int i;
 	int err = 0;
 
-	for (i = 0; i < ctx->cfg->num_chars; i++) {
+	for (i = 0; i < linedisp->num_chars; i++) {
 		err = sead3_wait_lcd_idle(ctx);
 		if (err)
 			break;
@@ -218,130 +214,6 @@ static const struct of_device_id img_ascii_lcd_matches[] = {
 };
 MODULE_DEVICE_TABLE(of, img_ascii_lcd_matches);
 
-/**
- * img_ascii_lcd_scroll() - scroll the display by a character
- * @t: really a pointer to the private data structure
- *
- * Scroll the current message along the LCD by one character, rearming the
- * timer if required.
- */
-static void img_ascii_lcd_scroll(struct timer_list *t)
-{
-	struct img_ascii_lcd_ctx *ctx = from_timer(ctx, t, timer);
-	unsigned int i, ch = ctx->scroll_pos;
-	unsigned int num_chars = ctx->cfg->num_chars;
-
-	/* update the current message string */
-	for (i = 0; i < num_chars;) {
-		/* copy as many characters from the string as possible */
-		for (; i < num_chars && ch < ctx->message_len; i++, ch++)
-			ctx->curr[i] = ctx->message[ch];
-
-		/* wrap around to the start of the string */
-		ch = 0;
-	}
-
-	/* update the LCD */
-	ctx->cfg->update(ctx);
-
-	/* move on to the next character */
-	ctx->scroll_pos++;
-	ctx->scroll_pos %= ctx->message_len;
-
-	/* rearm the timer */
-	if (ctx->message_len > ctx->cfg->num_chars)
-		mod_timer(&ctx->timer, jiffies + ctx->scroll_rate);
-}
-
-/**
- * img_ascii_lcd_display() - set the message to be displayed
- * @ctx: pointer to the private data structure
- * @msg: the message to display
- * @count: length of msg, or -1
- *
- * Display a new message @msg on the LCD. @msg can be longer than the number of
- * characters the LCD can display, in which case it will begin scrolling across
- * the LCD display.
- *
- * Return: 0 on success, -ENOMEM on memory allocation failure
- */
-static int img_ascii_lcd_display(struct img_ascii_lcd_ctx *ctx,
-			     const char *msg, ssize_t count)
-{
-	char *new_msg;
-
-	/* stop the scroll timer */
-	del_timer_sync(&ctx->timer);
-
-	if (count == -1)
-		count = strlen(msg);
-
-	/* if the string ends with a newline, trim it */
-	if (msg[count - 1] == '\n')
-		count--;
-
-	new_msg = devm_kmalloc(&ctx->pdev->dev, count + 1, GFP_KERNEL);
-	if (!new_msg)
-		return -ENOMEM;
-
-	memcpy(new_msg, msg, count);
-	new_msg[count] = 0;
-
-	if (ctx->message)
-		devm_kfree(&ctx->pdev->dev, ctx->message);
-
-	ctx->message = new_msg;
-	ctx->message_len = count;
-	ctx->scroll_pos = 0;
-
-	/* update the LCD */
-	img_ascii_lcd_scroll(&ctx->timer);
-
-	return 0;
-}
-
-/**
- * message_show() - read message via sysfs
- * @dev: the LCD device
- * @attr: the LCD message attribute
- * @buf: the buffer to read the message into
- *
- * Read the current message being displayed or scrolled across the LCD display
- * into @buf, for reads from sysfs.
- *
- * Return: the number of characters written to @buf
- */
-static ssize_t message_show(struct device *dev, struct device_attribute *attr,
-			    char *buf)
-{
-	struct img_ascii_lcd_ctx *ctx = dev_get_drvdata(dev);
-
-	return sprintf(buf, "%s\n", ctx->message);
-}
-
-/**
- * message_store() - write a new message via sysfs
- * @dev: the LCD device
- * @attr: the LCD message attribute
- * @buf: the buffer containing the new message
- * @count: the size of the message in @buf
- *
- * Write a new message to display or scroll across the LCD display from sysfs.
- *
- * Return: the size of the message on success, else -ERRNO
- */
-static ssize_t message_store(struct device *dev, struct device_attribute *attr,
-			     const char *buf, size_t count)
-{
-	struct img_ascii_lcd_ctx *ctx = dev_get_drvdata(dev);
-	int err;
-
-	err = img_ascii_lcd_display(ctx, buf, count);
-	return err ?: count;
-}
-
-static DEVICE_ATTR_RW(message);
-
 /**
  * img_ascii_lcd_probe() - probe an LCD display device
  * @pdev: the LCD platform device
@@ -355,26 +227,25 @@ static int img_ascii_lcd_probe(struct platform_device *pdev)
 {
 	const struct of_device_id *match;
 	const struct img_ascii_lcd_config *cfg;
+	struct device *dev = &pdev->dev;
 	struct img_ascii_lcd_ctx *ctx;
 	int err;
 
-	match = of_match_device(img_ascii_lcd_matches, &pdev->dev);
+	match = of_match_device(img_ascii_lcd_matches, dev);
 	if (!match)
 		return -ENODEV;
 
 	cfg = match->data;
-	ctx = devm_kzalloc(&pdev->dev, sizeof(*ctx) + cfg->num_chars,
-			   GFP_KERNEL);
+	ctx = devm_kzalloc(dev, sizeof(*ctx) + cfg->num_chars, GFP_KERNEL);
 	if (!ctx)
 		return -ENOMEM;
 
 	if (cfg->external_regmap) {
-		ctx->regmap = syscon_node_to_regmap(pdev->dev.parent->of_node);
+		ctx->regmap = syscon_node_to_regmap(dev->parent->of_node);
 		if (IS_ERR(ctx->regmap))
 			return PTR_ERR(ctx->regmap);
 
-		if (of_property_read_u32(pdev->dev.of_node, "offset",
-					 &ctx->offset))
+		if (of_property_read_u32(dev->of_node, "offset", &ctx->offset))
 			return -EINVAL;
 	} else {
 		ctx->base = devm_platform_ioremap_resource(pdev, 0);
@@ -382,29 +253,23 @@ static int img_ascii_lcd_probe(struct platform_device *pdev)
 			return PTR_ERR(ctx->base);
 	}
 
-	ctx->pdev = pdev;
-	ctx->cfg = cfg;
-	ctx->message = NULL;
-	ctx->scroll_pos = 0;
-	ctx->scroll_rate = HZ / 2;
-
-	/* initialise a timer for scrolling the message */
-	timer_setup(&ctx->timer, img_ascii_lcd_scroll, 0);
-
-	platform_set_drvdata(pdev, ctx);
-
-	/* display a default message */
-	err = img_ascii_lcd_display(ctx, "Linux " UTS_RELEASE "       ", -1);
+	err = linedisp_register(&ctx->linedisp, dev, cfg->num_chars, ctx->curr,
+				cfg->update);
 	if (err)
-		goto out_del_timer;
+		return err;
 
-	err = device_create_file(&pdev->dev, &dev_attr_message);
+	/* for backwards compatibility */
+	err = compat_only_sysfs_link_entry_to_kobj(&dev->kobj,
+						   &ctx->linedisp.dev.kobj,
+						   "message", NULL);
 	if (err)
-		goto out_del_timer;
+		goto err_unregister;
 
+	platform_set_drvdata(pdev, ctx);
 	return 0;
-out_del_timer:
-	del_timer_sync(&ctx->timer);
+
+err_unregister:
+	linedisp_unregister(&ctx->linedisp);
 	return err;
 }
 
@@ -421,8 +286,8 @@ static int img_ascii_lcd_remove(struct platform_device *pdev)
 {
 	struct img_ascii_lcd_ctx *ctx = platform_get_drvdata(pdev);
 
-	device_remove_file(&pdev->dev, &dev_attr_message);
-	del_timer_sync(&ctx->timer);
+	sysfs_remove_link(&pdev->dev.kobj, "message");
+	linedisp_unregister(&ctx->linedisp);
 	return 0;
 }
 

drivers/auxdisplay/ks0108.c

@@ -15,10 +15,7 @@
 #include <linux/module.h>
 #include <linux/kernel.h>
 #include <linux/delay.h>
-#include <linux/fs.h>
-#include <linux/io.h>
 #include <linux/parport.h>
-#include <linux/uaccess.h>
 #include <linux/ks0108.h>
 
 #define KS0108_NAME "ks0108"

drivers/auxdisplay/line-display.c

+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Character line display core support
+ *
+ * Copyright (C) 2016 Imagination Technologies
+ * Author: Paul Burton <paul.burton@mips.com>
+ *
+ * Copyright (C) 2021 Glider bv
+ */
+
+#include <generated/utsrelease.h>
+
+#include <linux/device.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/sysfs.h>
+#include <linux/timer.h>
+
+#include "line-display.h"
+
+#define DEFAULT_SCROLL_RATE	(HZ / 2)
+
+/**
+ * linedisp_scroll() - scroll the display by a character
+ * @t: really a pointer to the private data structure
+ *
+ * Scroll the current message along the display by one character, rearming the
+ * timer if required.
+ */
+static void linedisp_scroll(struct timer_list *t)
+{
+	struct linedisp *linedisp = from_timer(linedisp, t, timer);
+	unsigned int i, ch = linedisp->scroll_pos;
+	unsigned int num_chars = linedisp->num_chars;
+
+	/* update the current message string */
+	for (i = 0; i < num_chars;) {
+		/* copy as many characters from the string as possible */
+		for (; i < num_chars && ch < linedisp->message_len; i++, ch++)
+			linedisp->buf[i] = linedisp->message[ch];
+
+		/* wrap around to the start of the string */
+		ch = 0;
+	}
+
+	/* update the display */
+	linedisp->update(linedisp);
+
+	/* move on to the next character */
+	linedisp->scroll_pos++;
+	linedisp->scroll_pos %= linedisp->message_len;
+
+	/* rearm the timer */
+	if (linedisp->message_len > num_chars && linedisp->scroll_rate)
+		mod_timer(&linedisp->timer, jiffies + linedisp->scroll_rate);
+}
+
+/**
+ * linedisp_display() - set the message to be displayed
+ * @linedisp: pointer to the private data structure
+ * @msg: the message to display
+ * @count: length of msg, or -1
+ *
+ * Display a new message @msg on the display. @msg can be longer than the
+ * number of characters the display can display, in which case it will begin
+ * scrolling across the display.
+ *
+ * Return: 0 on success, -ENOMEM on memory allocation failure
+ */
+static int linedisp_display(struct linedisp *linedisp, const char *msg,
+			    ssize_t count)
+{
+	char *new_msg;
+
+	/* stop the scroll timer */
+	del_timer_sync(&linedisp->timer);
+
+	if (count == -1)
+		count = strlen(msg);
+
+	/* if the string ends with a newline, trim it */
+	if (msg[count - 1] == '\n')
+		count--;
+
+	if (!count) {
+		/* Clear the display */
+		kfree(linedisp->message);
+		linedisp->message = NULL;
+		linedisp->message_len = 0;
+		memset(linedisp->buf, ' ', linedisp->num_chars);
+		linedisp->update(linedisp);
+		return 0;
+	}
+
+	new_msg = kmemdup_nul(msg, count, GFP_KERNEL);
+	if (!new_msg)
+		return -ENOMEM;
+
+	kfree(linedisp->message);
+
+	linedisp->message = new_msg;
+	linedisp->message_len = count;
+	linedisp->scroll_pos = 0;
+
+	/* update the display */
+	linedisp_scroll(&linedisp->timer);
+
+	return 0;
+}
+
+/**
+ * message_show() - read message via sysfs
+ * @dev: the display device
+ * @attr: the display message attribute
+ * @buf: the buffer to read the message into
+ *
+ * Read the current message being displayed or scrolled across the display into
+ * @buf, for reads from sysfs.
+ *
+ * Return: the number of characters written to @buf
+ */
+static ssize_t message_show(struct device *dev, struct device_attribute *attr,
+			    char *buf)
+{
+	struct linedisp *linedisp = container_of(dev, struct linedisp, dev);
+
+	return sysfs_emit(buf, "%s\n", linedisp->message);
+}
+
+/**
+ * message_store() - write a new message via sysfs
+ * @dev: the display device
+ * @attr: the display message attribute
+ * @buf: the buffer containing the new message
+ * @count: the size of the message in @buf
+ *
+ * Write a new message to display or scroll across the display from sysfs.
+ *
+ * Return: the size of the message on success, else -ERRNO
+ */
+static ssize_t message_store(struct device *dev, struct device_attribute *attr,
+			     const char *buf, size_t count)
+{
+	struct linedisp *linedisp = container_of(dev, struct linedisp, dev);
+	int err;
+
+	err = linedisp_display(linedisp, buf, count);
+	return err ?: count;
+}
+
+static DEVICE_ATTR_RW(message);
+
+static ssize_t scroll_step_ms_show(struct device *dev,
+				   struct device_attribute *attr, char *buf)
+{
+	struct linedisp *linedisp = container_of(dev, struct linedisp, dev);
+
+	return sysfs_emit(buf, "%u\n", jiffies_to_msecs(linedisp->scroll_rate));
+}
+
+static ssize_t scroll_step_ms_store(struct device *dev,
+				    struct device_attribute *attr,
+				    const char *buf, size_t count)
+{
+	struct linedisp *linedisp = container_of(dev, struct linedisp, dev);
+	unsigned int ms;
+
+	if (kstrtouint(buf, 10, &ms) != 0)
+		return -EINVAL;
+
+	linedisp->scroll_rate = msecs_to_jiffies(ms);
+	if (linedisp->message && linedisp->message_len > linedisp->num_chars) {
+		del_timer_sync(&linedisp->timer);
+		if (linedisp->scroll_rate)
+			linedisp_scroll(&linedisp->timer);
+	}
+
+	return count;
+}
+
+static DEVICE_ATTR_RW(scroll_step_ms);
+
+static struct attribute *linedisp_attrs[] = {
+	&dev_attr_message.attr,
+	&dev_attr_scroll_step_ms.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(linedisp);
+
+static const struct device_type linedisp_type = {
+	.groups	= linedisp_groups,
+};
+
+/**
+ * linedisp_register - register a character line display
+ * @linedisp: pointer to character line display structure
+ * @parent: parent device
+ * @num_chars: the number of characters that can be displayed
+ * @buf: pointer to a buffer that can hold @num_chars characters
+ * @update: Function called to update the display.  This must not sleep!
+ *
+ * Return: zero on success, else a negative error code.
+ */
+int linedisp_register(struct linedisp *linedisp, struct device *parent,
+		      unsigned int num_chars, char *buf,
+		      void (*update)(struct linedisp *linedisp))
+{
+	static atomic_t linedisp_id = ATOMIC_INIT(-1);
+	int err;
+
+	memset(linedisp, 0, sizeof(*linedisp));
+	linedisp->dev.parent = parent;
+	linedisp->dev.type = &linedisp_type;
+	linedisp->update = update;
+	linedisp->buf = buf;
+	linedisp->num_chars = num_chars;
+	linedisp->scroll_rate = DEFAULT_SCROLL_RATE;
+
+	device_initialize(&linedisp->dev);
+	dev_set_name(&linedisp->dev, "linedisp.%lu",
+		     (unsigned long)atomic_inc_return(&linedisp_id));
+
+	/* initialise a timer for scrolling the message */
+	timer_setup(&linedisp->timer, linedisp_scroll, 0);
+
+	err = device_add(&linedisp->dev);
+	if (err)
+		goto out_del_timer;
+
+	/* display a default message */
+	err = linedisp_display(linedisp, "Linux " UTS_RELEASE "       ", -1);
+	if (err)
+		goto out_del_dev;
+
+	return 0;
+
+out_del_dev:
+	device_del(&linedisp->dev);
+out_del_timer:
+	del_timer_sync(&linedisp->timer);
+	put_device(&linedisp->dev);
+	return err;
+}
+EXPORT_SYMBOL_GPL(linedisp_register);
+
+/**
+ * linedisp_unregister - unregister a character line display
+ * @linedisp: pointer to character line display structure registered previously
+ *	      with linedisp_register()
+ */
+void linedisp_unregister(struct linedisp *linedisp)
+{
+	device_del(&linedisp->dev);
+	del_timer_sync(&linedisp->timer);
+	kfree(linedisp->message);
+	put_device(&linedisp->dev);
+}
+EXPORT_SYMBOL_GPL(linedisp_unregister);
+
+MODULE_LICENSE("GPL");

drivers/auxdisplay/line-display.h

+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Character line display core support
+ *
+ * Copyright (C) 2016 Imagination Technologies
+ * Author: Paul Burton <paul.burton@mips.com>
+ *
+ * Copyright (C) 2021 Glider bv
+ */
+
+#ifndef _LINEDISP_H
+#define _LINEDISP_H
+
+/**
+ * struct linedisp - character line display private data structure
+ * @dev: the line display device
+ * @timer: timer used to implement scrolling
+ * @update: function called to update the display
+ * @buf: pointer to the buffer for the string currently displayed
+ * @message: the full message to display or scroll on the display
+ * @num_chars: the number of characters that can be displayed
+ * @message_len: the length of the @message string
+ * @scroll_pos: index of the first character of @message currently displayed
+ * @scroll_rate: scroll interval in jiffies
+ */
+struct linedisp {
+	struct device dev;
+	struct timer_list timer;
+	void (*update)(struct linedisp *linedisp);
+	char *buf;
+	char *message;
+	unsigned int num_chars;
+	unsigned int message_len;
+	unsigned int scroll_pos;
+	unsigned int scroll_rate;
+};
+
+int linedisp_register(struct linedisp *linedisp, struct device *parent,
+		      unsigned int num_chars, char *buf,
+		      void (*update)(struct linedisp *linedisp));
+void linedisp_unregister(struct linedisp *linedisp);
+
+#endif /* LINEDISP_H */

include/uapi/linux/map_to_14segment.h

+/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
+/*
+ * Copyright (C) 2021 Glider bv
+ *
+ * Based on include/uapi/linux/map_to_7segment.h:
+
+ * Copyright (c) 2005 Henk Vergonet <Henk.Vergonet@gmail.com>
+ */
+
+#ifndef MAP_TO_14SEGMENT_H
+#define MAP_TO_14SEGMENT_H
+
+/* This file provides translation primitives and tables for the conversion
+ * of (ASCII) characters to a 14-segments notation.
+ *
+ * The 14 segment's wikipedia notation below is used as standard.
+ * See: https://en.wikipedia.org/wiki/Fourteen-segment_display
+ *
+ * Notation:	+---a---+
+ *		|\  |  /|
+ *		f h i j b
+ *		|  \|/  |
+ *		+-g1+-g2+
+ *		|  /|\  |
+ *		e k l m c
+ *		|/  |  \|
+ *		+---d---+
+ *
+ * Usage:
+ *
+ *   Register a map variable, and fill it with a character set:
+ *	static SEG14_DEFAULT_MAP(map_seg14);
+ *
+ *
+ *   Then use for conversion:
+ *	seg14 = map_to_seg14(&map_seg14, some_char);
+ *	...
+ *
+ * In device drivers it is recommended, if required, to make the char map
+ * accessible via the sysfs interface using the following scheme:
+ *
+ * static ssize_t map_seg14_show(struct device *dev,
+ *				 struct device_attribute *attr, char *buf)
+ * {
+ *	memcpy(buf, &map_seg14, sizeof(map_seg14));
+ *	return sizeof(map_seg14);
+ * }
+ * static ssize_t map_seg14_store(struct device *dev,
+ *				  struct device_attribute *attr,
+ *				  const char *buf, size_t cnt)
+ * {
+ *	if (cnt != sizeof(map_seg14))
+ *		return -EINVAL;
+ *	memcpy(&map_seg14, buf, cnt);
+ *	return cnt;
+ * }
+ * static DEVICE_ATTR_RW(map_seg14);
+ */
+#include <linux/errno.h>
+#include <linux/types.h>
+
+#include <asm/byteorder.h>
+
+#define BIT_SEG14_A		0
+#define BIT_SEG14_B		1
+#define BIT_SEG14_C		2
+#define BIT_SEG14_D		3
+#define BIT_SEG14_E		4
+#define BIT_SEG14_F		5
+#define BIT_SEG14_G1		6
+#define BIT_SEG14_G2		7
+#define BIT_SEG14_H		8
+#define BIT_SEG14_I		9
+#define BIT_SEG14_J		10
+#define BIT_SEG14_K		11
+#define BIT_SEG14_L		12
+#define BIT_SEG14_M		13
+#define BIT_SEG14_RESERVED1	14
+#define BIT_SEG14_RESERVED2	15
+
+struct seg14_conversion_map {
+	__be16 table[128];
+};
+
+static __inline__ int map_to_seg14(struct seg14_conversion_map *map, int c)
+{
+	if (c < 0 || c >= sizeof(map->table) / sizeof(map->table[0]))
+		return -EINVAL;
+
+	return __be16_to_cpu(map->table[c]);
+}
+
+#define SEG14_CONVERSION_MAP(_name, _map)	\
+	struct seg14_conversion_map _name = { .table = { _map } }
+
+/*
+ * It is recommended to use a facility that allows user space to redefine
+ * custom character sets for LCD devices. Please use a sysfs interface
+ * as described above.
+ */
+#define MAP_TO_SEG14_SYSFS_FILE	"map_seg14"
+
+/*******************************************************************************
+ * ASCII conversion table
+ ******************************************************************************/
+
+#define _SEG14(sym, a, b, c, d, e, f, g1, g2, h, j, k, l, m, n)	\
+	__cpu_to_be16( a << BIT_SEG14_A  |  b << BIT_SEG14_B  |	\
+		       c << BIT_SEG14_C  |  d << BIT_SEG14_D  |	\
+		       e << BIT_SEG14_E  |  f << BIT_SEG14_F  |	\
+		      g1 << BIT_SEG14_G1 | g2 << BIT_SEG14_G2 |	\
+		       h << BIT_SEG14_H  |  j << BIT_SEG14_I  |	\
+		       k << BIT_SEG14_J  |  l << BIT_SEG14_K  |	\
+		       m << BIT_SEG14_L  |  n << BIT_SEG14_M )
+
+#define _MAP_0_32_ASCII_SEG14_NON_PRINTABLE				\
+	0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
+
+#define _MAP_33_47_ASCII_SEG14_SYMBOL				\
+	_SEG14('!', 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('"', 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0),	\
+	_SEG14('#', 0, 1, 1, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1, 0),	\
+	_SEG14('$', 1, 0, 1, 1, 0, 1, 1, 1, 0, 1, 0, 0, 1, 0),	\
+	_SEG14('%', 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 1, 1, 0, 0),	\
+	_SEG14('&', 1, 0, 0, 1, 1, 0, 1, 0, 1, 0, 1, 0, 0, 1),	\
+	_SEG14('\'',0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0),	\
+	_SEG14('(', 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1),	\
+	_SEG14(')', 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0),	\
+	_SEG14('*', 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1),	\
+	_SEG14('+', 0, 0, 0, 0, 0, 0, 1, 1, 0, 1, 0, 0, 1, 0),	\
+	_SEG14(',', 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0),	\
+	_SEG14('-', 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('.', 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1),	\
+	_SEG14('/', 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0),
+
+#define _MAP_48_57_ASCII_SEG14_NUMERIC				\
+	_SEG14('0', 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 0, 0),	\
+	_SEG14('1', 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0),	\
+	_SEG14('2', 1, 1, 0, 1, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('3', 1, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('4', 0, 1, 1, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('5', 1, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0, 1),	\
+	_SEG14('6', 1, 0, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('7', 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0),	\
+	_SEG14('8', 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('9', 1, 1, 1, 1, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0),
+
+#define _MAP_58_64_ASCII_SEG14_SYMBOL				\
+	_SEG14(':', 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0),	\
+	_SEG14(';', 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0),	\
+	_SEG14('<', 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1),	\
+	_SEG14('=', 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('>', 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 1, 0, 0),	\
+	_SEG14('?', 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 1, 0),	\
+	_SEG14('@', 1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 0, 0, 0, 0),
+
+#define _MAP_65_90_ASCII_SEG14_ALPHA_UPPER			\
+	_SEG14('A', 1, 1, 1, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('B', 1, 1, 1, 1, 0, 0, 0, 1, 0, 1, 0, 0, 1, 0),	\
+	_SEG14('C', 1, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('D', 1, 1, 1, 1, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0),	\
+	_SEG14('E', 1, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('F', 1, 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('G', 1, 0, 1, 1, 1, 1, 0, 1, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('H', 0, 1, 1, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('I', 1, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0),	\
+	_SEG14('J', 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('K', 0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 1, 0, 0, 1),	\
+	_SEG14('L', 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('M', 0, 1, 1, 0, 1, 1, 0, 0, 1, 0, 1, 0, 0, 0),	\
+	_SEG14('N', 0, 1, 1, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0, 1),	\
+	_SEG14('O', 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('P', 1, 1, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('Q', 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 1),	\
+	_SEG14('R', 1, 1, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 1),	\
+	_SEG14('S', 1, 0, 1, 1, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('T', 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0),	\
+	_SEG14('U', 0, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('V', 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 1, 1, 0, 0),	\
+	_SEG14('W', 0, 1, 1, 0, 1, 1, 0, 0, 0, 0, 0, 1, 0, 1),	\
+	_SEG14('X', 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 1, 0, 1),	\
+	_SEG14('Y', 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 1, 0),	\
+	_SEG14('Z', 1, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0),
+
+#define _MAP_91_96_ASCII_SEG14_SYMBOL				\
+	_SEG14('[', 1, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('\\',0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1),	\
+	_SEG14(']', 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('^', 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1),	\
+	_SEG14('_', 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('`', 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0),
+
+#define _MAP_97_122_ASCII_SEG14_ALPHA_LOWER			\
+	_SEG14('a', 0, 0, 0, 1, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0),	\
+	_SEG14('b', 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 1),	\
+	_SEG14('c', 0, 0, 0, 1, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('d', 0, 1, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0),	\
+	_SEG14('e', 0, 0, 0, 1, 1, 0, 1, 0, 0, 0, 0, 1, 0, 0),	\
+	_SEG14('f', 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 1, 0, 1, 0),	\
+	_SEG14('g', 0, 1, 1, 1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0),	\
+	_SEG14('h', 0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 0),	\
+	_SEG14('i', 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0),	\
+	_SEG14('j', 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 1, 0, 0),	\
+	_SEG14('k', 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 1, 1),	\
+	_SEG14('l', 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('m', 0, 0, 1, 0, 1, 0, 1, 1, 0, 0, 0, 0, 1, 0),	\
+	_SEG14('n', 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 0),	\
+	_SEG14('o', 0, 0, 1, 1, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('p', 0, 0, 0, 0, 1, 1, 1, 0, 1, 0, 0, 0, 0, 0),	\
+	_SEG14('q', 0, 1, 1, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0),	\
+	_SEG14('r', 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('s', 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1),	\
+	_SEG14('t', 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('u', 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0),	\
+	_SEG14('v', 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0),	\
+	_SEG14('w', 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 1),	\
+	_SEG14('x', 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 1, 0, 1),	\
+	_SEG14('y', 0, 1, 1, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0),	\
+	_SEG14('z', 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0),
+
+#define _MAP_123_126_ASCII_SEG14_SYMBOL				\
+	_SEG14('{', 1, 0, 0, 1, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0),	\
+	_SEG14('|', 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0),	\
+	_SEG14('}', 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 1),	\
+	_SEG14('~', 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0),
+
+/* Maps */
+#define MAP_ASCII14SEG_ALPHANUM			\
+	_MAP_0_32_ASCII_SEG14_NON_PRINTABLE	\
+	_MAP_33_47_ASCII_SEG14_SYMBOL		\
+	_MAP_48_57_ASCII_SEG14_NUMERIC		\
+	_MAP_58_64_ASCII_SEG14_SYMBOL		\
+	_MAP_65_90_ASCII_SEG14_ALPHA_UPPER	\
+	_MAP_91_96_ASCII_SEG14_SYMBOL		\
+	_MAP_97_122_ASCII_SEG14_ALPHA_LOWER	\
+	_MAP_123_126_ASCII_SEG14_SYMBOL
+
+#define SEG14_DEFAULT_MAP(_name)		\
+	SEG14_CONVERSION_MAP(_name, MAP_ASCII14SEG_ALPHANUM)
+
+#endif	/* MAP_TO_14SEGMENT_H */