linux-kernel - Re: [PATCH 3/3] drivers: auxdisplay: Add JHD1313 I2C interface driver

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Message-ID: <41212589-163f-63a2-38ab-1a1fb05f4813@kernel.org>
Date:   Thu, 28 Nov 2019 14:08:13 +0000
From:   Kieran Bingham <kbingham@...nel.org>
To:     Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        devicetree@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Simon Goda <simon.goda@...los.com>
Subject: Re: [PATCH 3/3] drivers: auxdisplay: Add JHD1313 I2C interface driver

Hi Miguel,

On 28/11/2019 13:43, Miguel Ojeda wrote:
> Hi Kieran,
> 
> On Thu, Nov 28, 2019 at 11:55 AM <kbingham@...nel.org> wrote:
>>
>> diff --git a/MAINTAINERS b/MAINTAINERS
>> index 8f075b866aaf..640f099ff7fb 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -8837,6 +8837,10 @@ S:       Maintained
>>  F:     Documentation/admin-guide/jfs.rst
>>  F:     fs/jfs/
>>
>> +JHD1313 LCD Dispaly driver
> 
> Typo (and it should be all uppercase; and perhaps "Display" is not
> needed given LCD is there; but see also comments on the title below).

Good spot, and good point "Liquid Crystal Display Display" is a bit
redundant.

> Also missing the "S:" entry.

Ah yes, I think we can add the following here:

S:      Maintained

>> diff --git a/drivers/auxdisplay/Kconfig b/drivers/auxdisplay/Kconfig
>> index b8313a04422d..cfc61c1abdee 100644
>> --- a/drivers/auxdisplay/Kconfig
>> +++ b/drivers/auxdisplay/Kconfig
>> @@ -27,6 +27,18 @@ config HD44780
>>           kernel and started at boot.
>>           If you don't understand what all this is about, say N.
>>
>> +config JHD1313
>> +       tristate "JHD1313 Character LCD support"
>> +       depends on I2C
>> +       select CHARLCD
>> +       ---help---
>> +         Enable support for Character LCDs using a JHD1313 controller on I2C.
>> +         The LCD is accessible through the /dev/lcd char device (10, 156).
>> +         This code can either be compiled as a module, or linked into the
>> +         kernel and started at boot.
>> +         This supports the LCD panel on the Grove 16x2 LCD series.
>> +         If you don't understand what all this is about, say N.
> 
> Would it be useful/worth for users to put "Grove series" and/or "I2C"
> in the tristate title? (i.e. like the help section explains and also
> like the MODULE_DESCRIPTION says).

I have struggled with the difference between the definition of this
driver (which supports a 'JHD1313') vs the 'product' that uses it (the
Grove display), and I also suspect that as it's just an implementation
of a more generic part, so I'm also contemplating renaming this. For
instance, the products at:

	http://www.jhdlcd.com.cn/162character.html

All seem to reference an SPLC780D controller, and have varying
properties of backlight colour, and text colour.

Thus I highly suspect that the JHD1313 is just a specific
variant/implementation of the range which is utilised by the Grove LCD
board. (which makes jhd1313 a bad name for this driver...)

Do you have any experience in these various part numbers, to suggest
perhaps a better naming?

Or I wonder if anyone has any relevant contacts at either Seeed, or JHD
or any other related part here...

Now that I track down the SPLC780D, I see:

	https://www.newhavendisplay.com/app_notes/SPLC780D.pdf

Which leads to 'yet another vendor', and actually I already see
newhaven,.* in vendor-prefixes.yaml ... however this looks like it
relates to just the 'LCD driver', and does not provide the I2C interface
- so the device is of course more complex than a single part.

Anyway, certainly adding in I2C would be beneficial though.


>> diff --git a/drivers/auxdisplay/jhd1313.c b/drivers/auxdisplay/jhd1313.c
>> new file mode 100644
>> index 000000000000..abf270e128ac
>> --- /dev/null
>> +++ b/drivers/auxdisplay/jhd1313.c
>> @@ -0,0 +1,111 @@
>> +// SPDX-License-Identifier: GPL-2.0+
>> +
> 
> Unconventional (AFAIK) empty line.

Ooops, I can drop that one :-D

> Thanks for the driver!

You're welcome. The charlcd_ framework makes it easy to add an LCD over
I2C, and I hope this can be useful to others.

> Cheers,
> Miguel

--
Kieran