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

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Date:   Thu, 20 Jul 2023 18:49:59 +0200
From:   poeschel@...onage.de
To:     Hugo Villeneuve <hugo@...ovil.com>
Cc:     Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Hugo Villeneuve <hvilleneuve@...onoff.com>,
        linux-kernel@...r.kernel.org, geert@...ux-m68k.org,
        Christian Meusel <christian.meusel@...teo.de>
Subject: Re: [PATCH] auxdisplay: hd44780: move cursor home after clear display
 command

Am 2023-07-06 21:49, schrieb Hugo Villeneuve:
> On Thu, 6 Jul 2023 21:33:05 +0200
> Miguel Ojeda <miguel.ojeda.sandonis@...il.com> wrote:
> 
>> On Thu, Jul 6, 2023 at 8:51 PM Hugo Villeneuve <hugo@...ovil.com> 
>> wrote:
>> >
>> > 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>
>> 
>> Thanks! Sounds good to me, as long the extra command does not
>> introduce some issue with the actual HD44780 -- can we double-check
>> the HD44780 still works as expected?
>> 
>> Cc'ing Lars and Geert since they may be able to give it a quick test.
> 
> Hi Miguel,
> I do not have a standard Hitachi controller to test it on, so lets wait
> for feedback from Lars and Geert or others.

Sorry guys,
I do not have access to the relevant hardware anymore. I am CC'ing 
Christian,
who has the relevant hardware and maybe he can help testing the patch.
Christian is on vacation up until mid august, so we have to wait a bit 
more
for someone able to test this.

BTW: The displays I did the work back then on were for sure not genuine
Hitachi ones either.
I do not see, that the little patch should do any harm.

Regards,
Lars