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

From: Robert Abel
Date: Sun Feb 25 2018 - 18:55:05 EST


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@xxxxxxxxxxxxx>
---
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