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

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Message-Id: <20230706185100.84322-1-hugo@hugovil.com>
Date:   Thu,  6 Jul 2023 14:50:59 -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] auxdisplay: hd44780: move cursor home after clear display command

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

The "clear display" 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 clear display
command.

Extract of CLEAR_DISPLAY 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 clear display command to support
non-standard LCDs.

Signed-off-by: Hugo Villeneuve <hvilleneuve@...onoff.com>
---
 drivers/auxdisplay/hd44780_common.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/auxdisplay/hd44780_common.c b/drivers/auxdisplay/hd44780_common.c
index 3934c2eebf33..70c818945a74 100644
--- a/drivers/auxdisplay/hd44780_common.c
+++ b/drivers/auxdisplay/hd44780_common.c
@@ -82,7 +82,13 @@ 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;
+
+	/*
+	 * Some LCDs (ex: NewHaven) do not reset the DDRAM address when
+	 * executing the CLEAR_DISPLAY command. Explicitely move cursor
+	 * to home position to account for these non-standard LCDs:
+	 */
+	return hd44780_common_home(lcd);
 }
 EXPORT_SYMBOL_GPL(hd44780_common_clear_display);
 

base-commit: c17414a273b81fe4e34e11d69fc30cc8b1431614
-- 
2.30.2