auxdisplay for v6.19-1

* Support linedisp attribute attachment to auxdisplay parent devices -----BEGIN PGP SIGNATURE----- iQIzBAABCgAdFiEEqaflIX74DDDzMJJtb7wzTHR8rCgFAmkljLUACgkQb7wzTHR8 rCgecQ//b6nPYBZsdtg9ZkOKmepHLu4mkHJIsNL2X+8aHvYC+lV24J9ABnbfKMlN R3DGSCoFH83ZuBXM0ZhAxs+xn3STCecC6t3g3ZP2QzG/5TQXvB2iHsNnAo401SLu buhu+EwTyawXJB8v4f7FZG+8UXz2pkk1uEV0zMaDE+nqzy+FplopPANQTYp0MFcz oxlxvkdQwxos8SqPeqsRsbr/6MSHLnKnUVgellbNyHwJa2C7d7gGmQ51aQkYM3zZ PAKrj9ruaoEBRXxDWZzForYLbPNyKe3c0aCY0T6AgcYmVT5ooPhoNWVGHYB9Q9F8 RrwZMJYA7lA8ml68vGPpftyEFUpZd9nHkXhIapFkv+jwFfhGId0F+b+3a2lLY7t4 PUJsjFkHoMlZpWJ03AAeJN6u2wFZEkpg7EfvOlzVl9b3QFcGHkvdjzQVNg8JQ5v8 rJ2ANkQPmdxwR2NFZHfrHW1WckLmnxBlYXFx/41Hx/bZD9H5XoYhj/j7izLPADEv wKxraS91db0RWzacQwlQTDPw/vG94F+OvW4t+lw5yxmVYWfnGjkH4R4Y2//yQqGh UmT+/t+Dms6/wyugBUSCjk0AE4i8Fs66Yyu6HALMqV7Fb2jhSPNyF1y5dtPQ5HOz hvWQwV6BOoOULbdbrdRwgp8h4qPAIyMMLcxXQHrxRn104R9RPzI= =4qpF -----END PGP SIGNATURE----- Merge tag 'auxdisplay-v6.19-1' of git://git.kernel.org/pub/scm/linux/kernel/git/andy/linux-auxdisplay Pull auxdisplay updates from Andy Shevchenko: - Support linedisp attribute attachment to auxdisplay parent devices * tag 'auxdisplay-v6.19-1' of git://git.kernel.org/pub/scm/linux/kernel/git/andy/linux-auxdisplay: auxdisplay: linedisp: support attribute attachment to auxdisplay devices auxdisplay: linedisp: add num_chars sysfs attribute auxdisplay: linedisp: display static message when length <= display size auxdisplay: linedisp: encapsulate container_of usage within to_linedisp docs: ABI: auxdisplay: document linedisp library sysfs attributes
2025-12-04 08:29:28 -08:00 · 2025-12-04 08:29:28 -08:00 · 94e244d9cc
parent d7aa60d966 00de283c53
commit 94e244d9cc
3 changed files with 312 additions and 22 deletions
--- a/Documentation/ABI/testing/sysfs-auxdisplay-linedisp
+++ 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/.../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
--- a/drivers/auxdisplay/line-display.c
+++ b/drivers/auxdisplay/line-display.c
@ -6,20 +6,23 @@
 * Author: Paul Burton <paul.burton@mips.com>
 *
 * Copyright (C) 2021 Glider bv
+ * Copyright (C) 2025 Jean-François Lessard
 */

 #ifndef CONFIG_PANEL_BOOT_MESSAGE
 #include <generated/utsrelease.h>
 #endif

-#include <linux/container_of.h>
+#include <linux/cleanup.h>
 #include <linux/device.h>
 #include <linux/export.h>
 #include <linux/idr.h>
 #include <linux/jiffies.h>
 #include <linux/kstrtox.h>
+#include <linux/list.h>
 #include <linux/module.h>
 #include <linux/slab.h>
+#include <linux/spinlock.h>
 #include <linux/string.h>
 #include <linux/sysfs.h>
 #include <linux/timer.h>
@ -31,6 +34,87 @@

 #define DEFAULT_SCROLL_RATE	(HZ / 2)

+/**
+ * struct linedisp_attachment - Holds the device to linedisp mapping
+ * @list: List entry for the linedisp_attachments list
+ * @device: Pointer to the device where linedisp attributes are added
+ * @linedisp: Pointer to the linedisp mapped to the device
+ * @direct: true for directly attached device using linedisp_attach(),
+ *	    false for child registered device using linedisp_register()
+ */
+struct linedisp_attachment {
+	struct list_head list;
+	struct device *device;
+	struct linedisp *linedisp;
+	bool direct;
+};
+
+static LIST_HEAD(linedisp_attachments);
+static DEFINE_SPINLOCK(linedisp_attachments_lock);
+
+static int create_attachment(struct device *dev, struct linedisp *linedisp, bool direct)
+{
+	struct linedisp_attachment *attachment;
+
+	attachment = kzalloc(sizeof(*attachment), GFP_KERNEL);
+	if (!attachment)
+		return -ENOMEM;
+
+	attachment->device = dev;
+	attachment->linedisp = linedisp;
+	attachment->direct = direct;
+
+	guard(spinlock)(&linedisp_attachments_lock);
+	list_add(&attachment->list, &linedisp_attachments);
+
+	return 0;
+}
+
+static struct linedisp *delete_attachment(struct device *dev, bool direct)
+{
+	struct linedisp_attachment *attachment;
+	struct linedisp *linedisp;
+
+	guard(spinlock)(&linedisp_attachments_lock);
+
+	list_for_each_entry(attachment, &linedisp_attachments, list) {
+		if (attachment->device == dev &&
+		    attachment->direct == direct)
+			break;
+	}
+
+	if (list_entry_is_head(attachment, &linedisp_attachments, list))
+		return NULL;
+
+	linedisp = attachment->linedisp;
+	list_del(&attachment->list);
+	kfree(attachment);
+
+	return linedisp;
+}
+
+static struct linedisp *to_linedisp(struct device *dev)
+{
+	struct linedisp_attachment *attachment;
+
+	guard(spinlock)(&linedisp_attachments_lock);
+
+	list_for_each_entry(attachment, &linedisp_attachments, list) {
+		if (attachment->device == dev)
+			break;
+	}
+
+	if (list_entry_is_head(attachment, &linedisp_attachments, list))
+		return NULL;
+
+	return attachment->linedisp;
+}
+
+static inline bool should_scroll(struct linedisp *linedisp)
+{
+	return linedisp->message_len > linedisp->num_chars && linedisp->scroll_rate;
+}
+
 /**
 * linedisp_scroll() - scroll the display by a character
 * @t: really a pointer to the private data structure
@ -62,8 +146,7 @@ static void linedisp_scroll(struct timer_list *t)
 	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);
+	mod_timer(&linedisp->timer, jiffies + linedisp->scroll_rate);
 }

 /**
@ -113,8 +196,16 @@ static int linedisp_display(struct linedisp *linedisp, const char *msg,
 	linedisp->message_len = count;
 	linedisp->scroll_pos = 0;

-	/* update the display */
-	linedisp_scroll(&linedisp->timer);
+	if (should_scroll(linedisp)) {
+		/* display scrolling message */
+		linedisp_scroll(&linedisp->timer);
+	} else {
+		/* display static message */
+		memset(linedisp->buf, ' ', linedisp->num_chars);
+		memcpy(linedisp->buf, linedisp->message,
+		       umin(linedisp->num_chars, linedisp->message_len));
+		linedisp->ops->update(linedisp);
+	}

 	return 0;
 }
@ -133,7 +224,7 @@ static int linedisp_display(struct linedisp *linedisp, const char *msg,
 static ssize_t message_show(struct device *dev, struct device_attribute *attr,
 			    char *buf)
 {
-	struct linedisp *linedisp = container_of(dev, struct linedisp, dev);
+	struct linedisp *linedisp = to_linedisp(dev);

 	return sysfs_emit(buf, "%s\n", linedisp->message);
 }
@ -152,7 +243,7 @@ static ssize_t message_show(struct device *dev, struct device_attribute *attr,
 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);
+	struct linedisp *linedisp = to_linedisp(dev);
 	int err;

 	err = linedisp_display(linedisp, buf, count);
@ -161,10 +252,20 @@ static ssize_t message_store(struct device *dev, struct device_attribute *attr,

 static DEVICE_ATTR_RW(message);

+static ssize_t num_chars_show(struct device *dev, struct device_attribute *attr,
+			      char *buf)
+{
+	struct linedisp *linedisp = to_linedisp(dev);
+
+	return sysfs_emit(buf, "%u\n", linedisp->num_chars);
+}
+
+static DEVICE_ATTR_RO(num_chars);
+
 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);
+	struct linedisp *linedisp = to_linedisp(dev);

 	return sysfs_emit(buf, "%u\n", jiffies_to_msecs(linedisp->scroll_rate));
 }
@ -173,7 +274,7 @@ 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);
+	struct linedisp *linedisp = to_linedisp(dev);
 	unsigned int ms;
 	int err;

@ -181,12 +282,12 @@ static ssize_t scroll_step_ms_store(struct device *dev,
 	if (err)
 		return err;

+	timer_delete_sync(&linedisp->timer);
+
 	linedisp->scroll_rate = msecs_to_jiffies(ms);
-	if (linedisp->message && linedisp->message_len > linedisp->num_chars) {
-		timer_delete_sync(&linedisp->timer);
-		if (linedisp->scroll_rate)
-			linedisp_scroll(&linedisp->timer);
-	}
+
+	if (should_scroll(linedisp))
+		linedisp_scroll(&linedisp->timer);

 	return count;
 }
@ -195,7 +296,7 @@ static DEVICE_ATTR_RW(scroll_step_ms);

 static ssize_t map_seg_show(struct device *dev, struct device_attribute *attr, char *buf)
 {
-	struct linedisp *linedisp = container_of(dev, struct linedisp, dev);
+	struct linedisp *linedisp = to_linedisp(dev);
 	struct linedisp_map *map = linedisp->map;

 	memcpy(buf, &map->map, map->size);
@ -205,7 +306,7 @@ static ssize_t map_seg_show(struct device *dev, struct device_attribute *attr, c
 static ssize_t map_seg_store(struct device *dev, struct device_attribute *attr,
 			     const char *buf, size_t count)
 {
-	struct linedisp *linedisp = container_of(dev, struct linedisp, dev);
+	struct linedisp *linedisp = to_linedisp(dev);
 	struct linedisp_map *map = linedisp->map;

 	if (count != map->size)
@ -223,6 +324,7 @@ static DEVICE_ATTR(map_seg14, 0644, map_seg_show, map_seg_store);

 static struct attribute *linedisp_attrs[] = {
 	&dev_attr_message.attr,
+	&dev_attr_num_chars.attr,
 	&dev_attr_scroll_step_ms.attr,
 	&dev_attr_map_seg7.attr,
 	&dev_attr_map_seg14.attr,
@ -232,7 +334,7 @@ static struct attribute *linedisp_attrs[] = {
 static umode_t linedisp_attr_is_visible(struct kobject *kobj, struct attribute *attr, int n)
 {
 	struct device *dev = kobj_to_dev(kobj);
-	struct linedisp *linedisp = container_of(dev, struct linedisp, dev);
+	struct linedisp *linedisp = to_linedisp(dev);
 	struct linedisp_map *map = linedisp->map;
 	umode_t mode = attr->mode;

@ -263,7 +365,7 @@ static DEFINE_IDA(linedisp_id);

 static void linedisp_release(struct device *dev)
 {
-	struct linedisp *linedisp = container_of(dev, struct linedisp, dev);
+	struct linedisp *linedisp = to_linedisp(dev);

 	kfree(linedisp->map);
 	kfree(linedisp->message);
@ -320,6 +422,90 @@ static int linedisp_init_map(struct linedisp *linedisp)
 #define LINEDISP_INIT_TEXT "Linux " UTS_RELEASE "       "
 #endif

+/**
+ * linedisp_attach - attach a character line display
+ * @linedisp: pointer to character line display structure
+ * @dev: pointer of the device to attach to
+ * @num_chars: the number of characters that can be displayed
+ * @ops: character line display operations
+ *
+ * Directly attach the line-display sysfs attributes to the passed device.
+ * The caller is responsible for calling linedisp_detach() to release resources
+ * after use.
+ *
+ * Return: zero on success, else a negative error code.
+ */
+int linedisp_attach(struct linedisp *linedisp, struct device *dev,
+		    unsigned int num_chars, const struct linedisp_ops *ops)
+{
+	int err;
+
+	memset(linedisp, 0, sizeof(*linedisp));
+	linedisp->ops = ops;
+	linedisp->num_chars = num_chars;
+	linedisp->scroll_rate = DEFAULT_SCROLL_RATE;
+
+	linedisp->buf = kzalloc(linedisp->num_chars, GFP_KERNEL);
+	if (!linedisp->buf)
+		return -ENOMEM;
+
+	/* initialise a character mapping, if required */
+	err = linedisp_init_map(linedisp);
+	if (err)
+		goto out_free_buf;
+
+	/* initialise a timer for scrolling the message */
+	timer_setup(&linedisp->timer, linedisp_scroll, 0);
+
+	err = create_attachment(dev, linedisp, true);
+	if (err)
+		goto out_del_timer;
+
+	/* display a default message */
+	err = linedisp_display(linedisp, LINEDISP_INIT_TEXT, -1);
+	if (err)
+		goto out_del_attach;
+
+	/* add attribute groups to target device */
+	err = device_add_groups(dev, linedisp_groups);
+	if (err)
+		goto out_del_attach;
+
+	return 0;
+
+out_del_attach:
+	delete_attachment(dev, true);
+out_del_timer:
+	timer_delete_sync(&linedisp->timer);
+out_free_buf:
+	kfree(linedisp->buf);
+	return err;
+}
+EXPORT_SYMBOL_NS_GPL(linedisp_attach, "LINEDISP");
+
+/**
+ * linedisp_detach - detach a character line display
+ * @dev: pointer of the device to detach from, that was previously
+ *	 attached with linedisp_attach()
+ */
+void linedisp_detach(struct device *dev)
+{
+	struct linedisp *linedisp;
+
+	linedisp = delete_attachment(dev, true);
+	if (!linedisp)
+		return;
+
+	timer_delete_sync(&linedisp->timer);
+
+	device_remove_groups(dev, linedisp_groups);
+
+	kfree(linedisp->map);
+	kfree(linedisp->message);
+	kfree(linedisp->buf);
+}
+EXPORT_SYMBOL_NS_GPL(linedisp_detach, "LINEDISP");
+
 /**
 * linedisp_register - register a character line display
 * @linedisp: pointer to character line display structure
@ -327,6 +513,11 @@ static int linedisp_init_map(struct linedisp *linedisp)
 * @num_chars: the number of characters that can be displayed
 * @ops: character line display operations
 *
+ * Register the line-display sysfs attributes to a new device named
+ * "linedisp.N" added to the passed parent device.
+ * The caller is responsible for calling linedisp_unregister() to release
+ * resources after use.
+ *
 * Return: zero on success, else a negative error code.
 */
 int linedisp_register(struct linedisp *linedisp, struct device *parent,
@ -362,19 +553,23 @@ int linedisp_register(struct linedisp *linedisp, struct device *parent,
 	/* initialise a timer for scrolling the message */
 	timer_setup(&linedisp->timer, linedisp_scroll, 0);

-	err = device_add(&linedisp->dev);
+	err = create_attachment(&linedisp->dev, linedisp, false);
 	if (err)
 		goto out_del_timer;

 	/* display a default message */
 	err = linedisp_display(linedisp, LINEDISP_INIT_TEXT, -1);
 	if (err)
-		goto out_del_dev;
+		goto out_del_attach;
+
+	err = device_add(&linedisp->dev);
+	if (err)
+		goto out_del_attach;

 	return 0;

-out_del_dev:
-	device_del(&linedisp->dev);
+out_del_attach:
+	delete_attachment(&linedisp->dev, false);
 out_del_timer:
 	timer_delete_sync(&linedisp->timer);
 out_put_device:
@ -391,6 +586,7 @@ EXPORT_SYMBOL_NS_GPL(linedisp_register, "LINEDISP");
 void linedisp_unregister(struct linedisp *linedisp)
 {
 	device_del(&linedisp->dev);
+	delete_attachment(&linedisp->dev, false);
 	timer_delete_sync(&linedisp->timer);
 	put_device(&linedisp->dev);
 }
--- a/drivers/auxdisplay/line-display.h
+++ b/drivers/auxdisplay/line-display.h
@ -6,6 +6,7 @@
 * Author: Paul Burton <paul.burton@mips.com>
 *
 * Copyright (C) 2021 Glider bv
+ * Copyright (C) 2025 Jean-François Lessard
 */

 #ifndef _LINEDISP_H
@ -81,6 +82,9 @@ struct linedisp {
 	unsigned int id;
 };

+int linedisp_attach(struct linedisp *linedisp, struct device *dev,
+		    unsigned int num_chars, const struct linedisp_ops *ops);
+void linedisp_detach(struct device *dev);
 int linedisp_register(struct linedisp *linedisp, struct device *parent,
 		      unsigned int num_chars, const struct linedisp_ops *ops);
 void linedisp_unregister(struct linedisp *linedisp);