[PATCH 4/4] auxdisplay: charlcd: make home command unshift display

[Robert Abel <rabel@robertabel.eu>]

A user has no way of unshifting the display programmatically once shifted.
Users cannot rely on ^[[H (home) to result in their message being seen either.
Use the actual HOME command 0x02 instead of only returning to x0/y0.
Users can still do ^[[Lx0y0; (go to x/y) if they wish to use the 'old' home
function.
Implement fast clearing of LCD by going to x0/y0 first, clearing display and
then calling home to possibly unshift display possibly avoiding artifacts by
not unshifting before clearing display.

Signed-off-by: Robert Abel <rabel@robertabel.eu>
---
 drivers/auxdisplay/charlcd.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/auxdisplay/charlcd.c b/drivers/auxdisplay/charlcd.c
index 24cabe88c7f0..41f9aa4a73d4 100644
--- a/drivers/auxdisplay/charlcd.c
+++ b/drivers/auxdisplay/charlcd.c
@@ -43,6 +43,8 @@
 /* LCD commands */
 #define LCD_CMD_DISPLAY_CLEAR	0x01	/* Clear entire display */
 
+#define LCD_CMD_HOME            0x02    /* Set DDRAM address to 0 and unshift display */
+
 #define LCD_CMD_ENTRY_MODE	0x04	/* Set entry mode */
 #define LCD_CMD_CURSOR_INC	0x02	/* Increment cursor */
 
@@ -182,7 +184,8 @@ static void charlcd_home(struct charlcd *lcd)
 
 	priv->addr.x = 0;
 	priv->addr.y = 0;
-	charlcd_gotoxy(lcd);
+	lcd->ops->write_cmd(lcd, LCD_CMD_HOME);
+	long_sleep(2);
 }
 
 static void charlcd_print(struct charlcd *lcd, char c)
@@ -202,9 +205,12 @@ static void charlcd_print(struct charlcd *lcd, char c)
 
 static void charlcd_clear_fast(struct charlcd *lcd)
 {
+	struct charlcd_priv *priv = to_priv(lcd);
 	int pos;
 
-	charlcd_home(lcd);
+	priv->addr.x = 0;
+	priv->addr.y = 0;
+	charlcd_gotoxy(lcd);
 
 	if (lcd->ops->clear_fast)
 		lcd->ops->clear_fast(lcd);
-- 
2.11.0