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Message-ID: <20250901020033.60196-5-jefflessard3@gmail.com>
Date: Sun, 31 Aug 2025 22:00:28 -0400
From: Jean-François Lessard <jefflessard3@...il.com>
To: Andy Shevchenko <andy@...nel.org>,
Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH 4/5] auxdisplay: linedisp: support attribute attachment to auxdisplay devices
Enable linedisp library integration into existing kernel devices (like LED
class) to provide a uniform 7-segment userspace API without creating
separate child devices, meeting the consistent interface while maintaining
coherent device hierarchies.
This allows uniform 7-segment API across all drivers while solving device
proliferation and fragmented userspace interfaces.
The provided attributes appear in two locations depending on usage:
1. On linedisp.N child devices (legacy linedisp_register())
2. On the parent auxdisplay device (new linedisp_attach())
Functionality is identical in both modes.
Existing consumers of linedisp_register() are unaffected. The new API
enables drivers like TM16XX to integrate 7-segment display functionality
seamlessly within their LED class device hierarchy.
Signed-off-by: Jean-François Lessard <jefflessard3@...il.com>
---
drivers/auxdisplay/line-display.c | 160 +++++++++++++++++++++++++++++-
drivers/auxdisplay/line-display.h | 4 +
2 files changed, 161 insertions(+), 3 deletions(-)
diff --git a/drivers/auxdisplay/line-display.c b/drivers/auxdisplay/line-display.c
index abeed8812..1176d46f0 100644
--- a/drivers/auxdisplay/line-display.c
+++ b/drivers/auxdisplay/line-display.c
@@ -6,20 +6,23 @@
* Author: Paul Burton <paul.burton@...s.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>
@@ -31,9 +34,72 @@
#define DEFAULT_SCROLL_RATE (HZ / 2)
+struct linedisp_attachment {
+ struct list_head list;
+ struct device *device;
+ struct linedisp *linedisp;
+ bool owns_device; /* true for child device mode, false for attached mode */
+};
+
+static LIST_HEAD(linedisp_attachments);
+static DEFINE_SPINLOCK(linedisp_attachments_lock);
+
+static int create_attachment(struct device *dev, struct linedisp *linedisp, bool owns_device)
+{
+ struct linedisp_attachment *attachment;
+
+ attachment = kzalloc(sizeof(*attachment), GFP_KERNEL);
+ if (!attachment)
+ return -ENOMEM;
+
+ attachment->device = dev;
+ attachment->linedisp = linedisp;
+ attachment->owns_device = owns_device;
+
+ guard(spinlock)(&linedisp_attachments_lock);
+ list_add(&attachment->list, &linedisp_attachments);
+
+ return 0;
+}
+
+static struct linedisp *delete_attachment(struct device *dev, bool owns_device)
+{
+ 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->owns_device == owns_device)
+ 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)
{
- return container_of(dev, struct linedisp, 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)
@@ -349,6 +415,87 @@ 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
+ *
+ * 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, false);
+ if (err)
+ goto out_del_timer;
+
+ /* add attribute groups to target device */
+ err = device_add_groups(dev, linedisp_groups);
+ if (err)
+ goto out_del_attach;
+
+ /* display a default message */
+ err = linedisp_display(linedisp, LINEDISP_INIT_TEXT, -1);
+ if (err)
+ goto out_rem_groups;
+
+ return 0;
+
+out_rem_groups:
+ device_remove_groups(dev, linedisp_groups);
+out_del_attach:
+ delete_attachment(dev, false);
+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 = delete_attachment(dev, false);
+
+ 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
@@ -391,10 +538,14 @@ 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, true);
if (err)
goto out_del_timer;
+ err = device_add(&linedisp->dev);
+ if (err)
+ goto out_del_attach;
+
/* display a default message */
err = linedisp_display(linedisp, LINEDISP_INIT_TEXT, -1);
if (err)
@@ -404,6 +555,8 @@ int linedisp_register(struct linedisp *linedisp, struct device *parent,
out_del_dev:
device_del(&linedisp->dev);
+out_del_attach:
+ delete_attachment(&linedisp->dev, true);
out_del_timer:
timer_delete_sync(&linedisp->timer);
out_put_device:
@@ -420,6 +573,7 @@ EXPORT_SYMBOL_NS_GPL(linedisp_register, "LINEDISP");
void linedisp_unregister(struct linedisp *linedisp)
{
device_del(&linedisp->dev);
+ delete_attachment(&linedisp->dev, true);
timer_delete_sync(&linedisp->timer);
put_device(&linedisp->dev);
}
diff --git a/drivers/auxdisplay/line-display.h b/drivers/auxdisplay/line-display.h
index 4348d7a2f..36853b639 100644
--- a/drivers/auxdisplay/line-display.h
+++ b/drivers/auxdisplay/line-display.h
@@ -6,6 +6,7 @@
* Author: Paul Burton <paul.burton@...s.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);
--
2.43.0
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