Commit 3ba5c78f authored by Jean-François Lessard's avatar Jean-François Lessard Committed by Andy Shevchenko
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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 sysfs attributes appear in one of the 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: default avatarJean-François Lessard <jefflessard3@gmail.com>
Signed-off-by: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
parent e2506346

drivers/auxdisplay/line-display.c

+174 −6
Original line number Diff line number Diff line
@@ -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>
@@ -31,9 +34,80 @@ 


#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)

{

	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)
@@ -348,6 +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
@@ -355,6 +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,
@@ -390,19 +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:
@@ -419,6 +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);

}

drivers/auxdisplay/line-display.h

+4 −0
Original line number Diff line number Diff line
@@ -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);