[06/17] auxdisplay: Extract character line display core support
diff mbox series

Message ID 20210322144848.1065067-7-geert@linux-m68k.org
State New, archived
Headers show
Series
  • auxdisplay: ht16k33: Add character display support
Related show

Commit Message

Geert Uytterhoeven March 22, 2021, 2:48 p.m. UTC
Extract the character line display core support from the simple ASCII
LCD driver for the MIPS Boston, Malta & SEAD3 development boards into
its own subdriver, so it can be reused for other displays.

Note that this moves the "message" device attribute in sysfs in a
"linedisp.N" subdirectory.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
---
Changes to img-ascii-lcd.c are untested due to lack of hardware.
---
 drivers/auxdisplay/Kconfig         |   8 +
 drivers/auxdisplay/Makefile        |   1 +
 drivers/auxdisplay/img-ascii-lcd.c | 198 +++----------------------
 drivers/auxdisplay/line-display.c  | 231 +++++++++++++++++++++++++++++
 drivers/auxdisplay/line-display.h  |  43 ++++++
 5 files changed, 304 insertions(+), 177 deletions(-)
 create mode 100644 drivers/auxdisplay/line-display.c
 create mode 100644 drivers/auxdisplay/line-display.h

Comments

Robin van der Gracht March 23, 2021, 8:18 a.m. UTC | #1
On 2021-03-22 15:48, Geert Uytterhoeven wrote:
> Extract the character line display core support from the simple ASCII
> LCD driver for the MIPS Boston, Malta & SEAD3 development boards into
> its own subdriver, so it can be reused for other displays.
> 
> Note that this moves the "message" device attribute in sysfs in a
> "linedisp.N" subdirectory.
> 
> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
> ---
> Changes to img-ascii-lcd.c are untested due to lack of hardware.
> ---
>  drivers/auxdisplay/Kconfig         |   8 +
>  drivers/auxdisplay/Makefile        |   1 +
>  drivers/auxdisplay/img-ascii-lcd.c | 198 +++----------------------
>  drivers/auxdisplay/line-display.c  | 231 +++++++++++++++++++++++++++++
>  drivers/auxdisplay/line-display.h  |  43 ++++++
>  5 files changed, 304 insertions(+), 177 deletions(-)
>  create mode 100644 drivers/auxdisplay/line-display.c
>  create mode 100644 drivers/auxdisplay/line-display.h
> 
> diff --git a/drivers/auxdisplay/Kconfig b/drivers/auxdisplay/Kconfig
> index 1509cb74705a30ad..42fc7b155de09dbc 100644
> --- a/drivers/auxdisplay/Kconfig
> +++ b/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
> @@ -169,6 +176,7 @@ config HT16K33
>  	select FB_SYS_IMAGEBLIT
>  	select INPUT_MATRIXKMAP
>  	select FB_BACKLIGHT
> +	select LINEDISP

At this point in your patch stack it's not used by the ht16k33 driver. I 
think it
would be nicer to add this dependency when the code actually starts 
depending on it.
So that when this patch stack gets applied partially or not in one go 
the chunks
would be independent.
Geert Uytterhoeven March 23, 2021, 8:52 a.m. UTC | #2
Hi Robin,

On Tue, Mar 23, 2021 at 9:18 AM robin <robin@protonic.nl> wrote:
> On 2021-03-22 15:48, Geert Uytterhoeven wrote:
> > Extract the character line display core support from the simple ASCII
> > LCD driver for the MIPS Boston, Malta & SEAD3 development boards into
> > its own subdriver, so it can be reused for other displays.
> >
> > Note that this moves the "message" device attribute in sysfs in a
> > "linedisp.N" subdirectory.
> >
> > Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

> > --- a/drivers/auxdisplay/Kconfig
> > +++ b/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
> > @@ -169,6 +176,7 @@ config HT16K33
> >       select FB_SYS_IMAGEBLIT
> >       select INPUT_MATRIXKMAP
> >       select FB_BACKLIGHT
> > +     select LINEDISP
>
> At this point in your patch stack it's not used by the ht16k33 driver. I
> think it
> would be nicer to add this dependency when the code actually starts
> depending on it.
> So that when this patch stack gets applied partially or not in one go
> the chunks
> would be independent.

Indeed, I messed up the order. Will fix.
Thanks for spotting!

Gr{oetje,eeting}s,

                        Geert

Patch
diff mbox series

diff --git a/drivers/auxdisplay/Kconfig b/drivers/auxdisplay/Kconfig
index 1509cb74705a30ad..42fc7b155de09dbc 100644
--- a/drivers/auxdisplay/Kconfig
+++ b/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
@@ -169,6 +176,7 @@  config HT16K33
 	select FB_SYS_IMAGEBLIT
 	select INPUT_MATRIXKMAP
 	select FB_BACKLIGHT
+	select LINEDISP
 	help
 	  Say yes here to add support for Holtek HT16K33, RAM mapping 16*8
 	  LED controller driver with keyscan.
diff --git a/drivers/auxdisplay/Makefile b/drivers/auxdisplay/Makefile
index 307771027c893a5b..6968ed4d3f0a8930 100644
--- a/drivers/auxdisplay/Makefile
+++ b/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
diff --git a/drivers/auxdisplay/img-ascii-lcd.c b/drivers/auxdisplay/img-ascii-lcd.c
index 2b5640b638900a90..4b6e4ac5ed977864 100644
--- a/drivers/auxdisplay/img-ascii-lcd.c
+++ b/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;
@@ -218,140 +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--;
-
-	if (!count) {
-		/* clear the LCD */
-		devm_kfree(&ctx->pdev->dev, ctx->message);
-		ctx->message = NULL;
-		ctx->message_len = 0;
-		memset(ctx->curr, ' ', ctx->cfg->num_chars);
-		ctx->cfg->update(ctx);
-		return 0;
-	}
-
-	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 sysfs_emit(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
@@ -391,30 +253,13 @@  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);
-	if (err)
-		goto out_del_timer;
-
-	err = device_create_file(dev, &dev_attr_message);
+	err = linedisp_register(&ctx->linedisp, dev, cfg->num_chars, ctx->curr,
+				cfg->update);
 	if (err)
-		goto out_del_timer;
+		return err;
 
+	platform_set_drvdata(pdev, ctx);
 	return 0;
-out_del_timer:
-	del_timer_sync(&ctx->timer);
-	return err;
 }
 
 /**
@@ -430,8 +275,7 @@  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);
+	linedisp_unregister(&ctx->linedisp);
 	return 0;
 }
 
diff --git a/drivers/auxdisplay/line-display.c b/drivers/auxdisplay/line-display.c
new file mode 100644
index 0000000000000000..4b97c20ac0b381ee
--- /dev/null
+++ b/drivers/auxdisplay/line-display.c
@@ -0,0 +1,231 @@ 
+// 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"
+
+/**
+ * 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)
+		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 = kmalloc(count + 1, GFP_KERNEL);
+	if (!new_msg)
+		return -ENOMEM;
+
+	memcpy(new_msg, msg, count);
+	new_msg[count] = 0;
+
+	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 struct attribute *linedisp_attrs[] = {
+	&dev_attr_message.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 = HZ / 2;
+
+	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");
diff --git a/drivers/auxdisplay/line-display.h b/drivers/auxdisplay/line-display.h
new file mode 100644
index 0000000000000000..0f5891d34c485871
--- /dev/null
+++ b/drivers/auxdisplay/line-display.h
@@ -0,0 +1,43 @@ 
+/* 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 */