linux-kernel - Re: [PATCH v7 4/5] iio: mcp9600: Recognize chip id for mcp9601

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Message-Id: <00D2ACBD-DE50-4132-8DF2-46DD97DBCE3B@watter.com>
Date: Wed, 20 Aug 2025 07:11:08 -0400
From: Ben Collins <bcollins@...ter.com>
To: Andy Shevchenko <andy.shevchenko@...il.com>
Cc: Jonathan Cameron <jic23@...nel.org>,
 David Lechner <dlechner@...libre.com>,
 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>,
 Andrew Hepp <andrew.hepp@...pp.dev>,
 linux-iio@...r.kernel.org,
 devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 4/5] iio: mcp9600: Recognize chip id for mcp9601


> On Aug 20, 2025, at 6:07 AM, Andy Shevchenko <andy.shevchenko@...il.com> wrote:
> 
> On Wed, Aug 20, 2025 at 2:45 AM Ben Collins <bcollins@...ter.com> wrote:
>> 
>> The current driver works with mcp9601, but emits a warning because it
>> does not recognize the chip id.
>> 
>> MCP9601 is a superset of MCP9600. The drivers works without changes
>> on this chipset.
>> 
>> However, the 9601 chip supports open/closed-circuit detection if wired
>> properly, so we'll need to be able to differentiate between them.
>> 
>> Moved "struct mcp9600_data" up in the file since a later patch will
>> need it and chip_info before the declerations.
> 
> declarations
> 
> ...
> 
>> +struct mcp9600_data {
>> +       struct i2c_client *client;
>> +};
>> +
>> #define MCP9600_CHANNELS(hj_num_ev, hj_ev_spec_off, cj_num_ev, cj_ev_spec_off) \
>>        {                                                                      \
>>                {                                                              \
>> @@ -123,10 +133,6 @@ static const struct iio_chan_spec mcp9600_channels[][2] = {
>>        MCP9600_CHANNELS(2, 0, 2, 0), /* Alerts: 1 2 3 4 */
>> };
>> 
>> -struct mcp9600_data {
>> -       struct i2c_client *client;
>> -};
>> -
> 
> It's not obvious why this piece of change is needed. AFAICS it's a stray change.

The explanation is in the changelog above. A follow up patch needs both struct
declarations to be where I added one and moved mcp9600_data to. It’s just ordering
so I don’t later have to forward declare new functions for filter_type, which make
use of these structs, but need to be in the iio_chan_spec mcp9600_channels[]
declaration.

I guess I could move mcp9600_data in that series, but I had this in here before
I split that series out, and it seemed simple enough to leave in.