linux-kernel - [PATCH v2] auxdisplay: hd44780: move cursor home after clear display command

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Message-Id: <20230722180925.1408885-1-hugo@hugovil.com>
Date:   Sat, 22 Jul 2023 14:09:25 -0400
From:   Hugo Villeneuve <hugo@...ovil.com>
To:     Miguel Ojeda <ojeda@...nel.org>
Cc:     hugo@...ovil.com, Hugo Villeneuve <hvilleneuve@...onoff.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2] auxdisplay: hd44780: move cursor home after clear display command

From: Hugo Villeneuve <hvilleneuve@...onoff.com>

The DISPLAY_CLEAR command on the NewHaven NHD-0220DZW-AG5 display
does NOT change the DDRAM address to 00h (home position) like the
standard Hitachi HD44780 controller. As a consequence, the starting
position of the initial string LCD_INIT_TEXT is not guaranteed to be
at 0,0 depending on where the cursor was before the DISPLAY_CLEAR
command.

Extract of DISPLAY_CLEAR command from datasheets of:

    Hitachi HD44780:
        ... It then sets DDRAM address 0 into the address counter...

    NewHaven NHD-0220DZW-AG5 datasheet:
	... This instruction does not change the DDRAM Address

Move the cursor home after sending DISPLAY_CLEAR command to support
non-standard LCDs.

Signed-off-by: Hugo Villeneuve <hvilleneuve@...onoff.com>
---
 drivers/auxdisplay/hd44780_common.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/auxdisplay/hd44780_common.c b/drivers/auxdisplay/hd44780_common.c
index 3934c2eebf33..7cbf375b0fa5 100644
--- a/drivers/auxdisplay/hd44780_common.c
+++ b/drivers/auxdisplay/hd44780_common.c
@@ -82,7 +82,15 @@ int hd44780_common_clear_display(struct charlcd *lcd)
 	hdc->write_cmd(hdc, LCD_CMD_DISPLAY_CLEAR);
 	/* datasheet says to wait 1,64 milliseconds */
 	long_sleep(2);
-	return 0;
+
+	/*
+	 * The Hitachi HD44780 controller (and compatible ones) reset the DDRAM
+	 * address when executing the DISPLAY_CLEAR command, thus the
+	 * following call is not required. However, other controllers do not
+	 * (e.g. NewHaven NHD-0220DZW-AG5), thus move the cursor to home
+	 * unconditionally to support both.
+	 */
+	return hd44780_common_home(lcd);
 }
 EXPORT_SYMBOL_GPL(hd44780_common_clear_display);
 

base-commit: d192f5382581d972c4ae1b4d72e0b59b34cadeb9
-- 
2.30.2