linux-kernel - Re: [PATCH 2/2] iio: dac: adding support for Microchip MCP47FEB02

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Message-ID: <3457c119-2f49-43a3-b96b-736b8f5de99b@baylibre.com>
Date: Mon, 22 Sep 2025 17:15:29 -0500
From: David Lechner <dlechner@...libre.com>
To: Nuno Sá <noname.nuno@...il.com>,
 Ariana Lazar <ariana.lazar@...rochip.com>,
 Jonathan Cameron <jic23@...nel.org>, Nuno Sá
 <nuno.sa@...log.com>, Andy Shevchenko <andy@...nel.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>
Cc: linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] iio: dac: adding support for Microchip MCP47FEB02

On 9/22/25 3:10 PM, Nuno Sá wrote:
> Hi Ariana,
> 
> Thanks for your patches. Some initial comments from me...
> 
> On Mon, 2025-09-22 at 14:30 +0300, Ariana Lazar wrote:

...

>> +static IIO_DEVICE_ATTR(store_eeprom, 0200, NULL, mcp47feb02_store_eeprom, 0);
>> +static struct attribute *mcp47feb02_attributes[] = {
>> +	&iio_dev_attr_store_eeprom.dev_attr.attr,
>> +	NULL,
>> +};
>> +
> 
> Not going to argue about the ABI for now but I don't think this is a standard one? So
> if acceptable you need an ABI doc.
> 
Here's a random idea. (I would wait for Jonathan to weigh in first before
assuming it is an acceptable idea though :-p)

The config registers are pretty much going to be a one-time deal. So those
could be written to only if they need it during probe.

For the voltage output registers, we could add extra out_voltageY channels
that are the power-on output state channels. So writing to out_voltageY_raw
wouldn't change any real output but would just be written to EEPROM. This
way these voltages could be controlled independently from the real outputs
and it uses existing ABI.

In any case, it would be interesting to hear more about how this chips are
actually used to better understand this EEPROM feature.