linux-kernel - [PATCH 3/5] auxdisplay: linedisp: add num

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Message-ID: <20250901020033.60196-4-jefflessard3@gmail.com>
Date: Sun, 31 Aug 2025 22:00:27 -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 3/5] auxdisplay: linedisp: add num_chars sysfs attribute

Add a read-only 'num_chars' sysfs attribute to report display digit count.

The num_chars attribute provides essential capability information to
userspace applications that need to know display dimensions before writing
messages, complementing the existing message and scroll controls.

No functional changes to existing behavior.

Signed-off-by: Jean-François Lessard <jefflessard3@...il.com>
---
 drivers/auxdisplay/line-display.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/auxdisplay/line-display.c b/drivers/auxdisplay/line-display.c
index ea23c43bb..abeed8812 100644
--- a/drivers/auxdisplay/line-display.c
+++ b/drivers/auxdisplay/line-display.c
@@ -211,6 +211,16 @@ static ssize_t scroll_step_ms_store(struct device *dev,
 
 static DEVICE_ATTR_RW(scroll_step_ms);
 
+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 map_seg_show(struct device *dev, struct device_attribute *attr, char *buf)
 {
 	struct linedisp *linedisp = to_linedisp(dev);
@@ -242,6 +252,7 @@ static DEVICE_ATTR(map_seg14, 0644, map_seg_show, map_seg_store);
 static struct attribute *linedisp_attrs[] = {
 	&dev_attr_message.attr,
 	&dev_attr_scroll_step_ms.attr,
+	&dev_attr_num_chars.attr,
 	&dev_attr_map_seg7.attr,
 	&dev_attr_map_seg14.attr,
 	NULL
-- 
2.43.0