[PATCH v2 10/15] auxdisplay: linedisp: Provide a small buffer in the struct linedisp

[Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>]

There is a driver that uses small buffer for the string, when we
add a new one, we may avoid duplication and use one provided by
the line display library. Allow user to skip buffer pointer when
registering a device.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
---
 drivers/auxdisplay/line-display.c | 4 ++--
 drivers/auxdisplay/line-display.h | 4 ++++
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/auxdisplay/line-display.c b/drivers/auxdisplay/line-display.c
index 75852ce6cc8d..d730cd0e1d03 100644
--- a/drivers/auxdisplay/line-display.c
+++ b/drivers/auxdisplay/line-display.c
@@ -330,8 +330,8 @@ int linedisp_register(struct linedisp *linedisp, struct device *parent,
 	linedisp->dev.parent = parent;
 	linedisp->dev.type = &linedisp_type;
 	linedisp->ops = ops;
-	linedisp->buf = buf;
-	linedisp->num_chars = num_chars;
+	linedisp->buf = buf ? buf : linedisp->curr;
+	linedisp->num_chars = buf ? num_chars : min(num_chars, LINEDISP_DEFAULT_BUF_SZ);
 	linedisp->scroll_rate = DEFAULT_SCROLL_RATE;
 
 	err = ida_alloc(&linedisp_id, GFP_KERNEL);
diff --git a/drivers/auxdisplay/line-display.h b/drivers/auxdisplay/line-display.h
index 65d782111f53..4c354b8f376e 100644
--- a/drivers/auxdisplay/line-display.h
+++ b/drivers/auxdisplay/line-display.h
@@ -54,12 +54,15 @@ struct linedisp_ops {
 	void (*update)(struct linedisp *linedisp);
 };
 
+#define LINEDISP_DEFAULT_BUF_SZ		8u
+
 /**
  * struct linedisp - character line display private data structure
  * @dev: the line display device
  * @id: instance id of this display
  * @timer: timer used to implement scrolling
  * @ops: character line display operations
+ * @curr: fallback buffer for the string
  * @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
@@ -73,6 +76,7 @@ struct linedisp {
 	struct timer_list timer;
 	const struct linedisp_ops *ops;
 	struct linedisp_map *map;
+	char curr[LINEDISP_DEFAULT_BUF_SZ];
 	char *buf;
 	char *message;
 	unsigned int num_chars;
-- 
2.43.0.rc1.1.gbec44491f096