Re: [RFC PATCH] hwmon: (jc42) Add I2C_CLASS_HWMON to detection class

[Guenter Roeck]

On 07/04/2016 04:04 PM, Alison Schofield wrote:
> On Mon, Jul 04, 2016 at 02:04:34PM -0700, Guenter Roeck wrote:
> > On 07/04/2016 12:19 PM, Alison Schofield wrote:
> > > In 2011, commit 774466add7c810fd7e4c8bcf41995b6799608880 changed
> > > the detection class of these chips to I2C_CLASS_SPD based on this
> > > premise: "makes more sense because these chips always live on
> > > memory modules"
> > >
> > > Today these chips have applications beyond memory modules.
> >
> > Do you have a specific example ?
> The mcp9808 is popular among hobbyists and makers in projects that
> monitor everything from their fish pond to their wine cellar. Beyond
> that I'm just referring to Microchips datasheet and marketing words
> saying that they target it for a wide range of apps beyond memory
> devices.  I guess the chance of one of them trying to use it, with a
> Linux driver, and caring about auto detect are pretty slim.

A better example would be the MCP9085, which is officially JC42.4 compliant
but also suggested for use as general purpose temperature sensor in its
datasheet.

I'll add your patch to -next.

Thanks,
Guenter

> As you've guessed, I changed the Diolan for my purposes. I just found
> it odd that jc42 was the only driver in hwmon, without I2C_CLASS_HWMON,
> so I thought it was worth a look and rethink.
>
> So, no, nothing broken, nothing suspected incompatible.
>
> alisons
>
>
> > > Add I2C_CLASS_HWMON as an additional detection class to allow
> > > detection by hwmon class i2c adapters.
> >
> > Practical impact should be limited, though. Most adapters have both
> > I2C_CLASS_HWMON and I2C_CLASS_SPD flags set. Besides the Diolan adapters,
> > which are experimental in nature anyway (and where it actually might make
> > sense to add I2C_CLASS_SPD), do you have an example where a JC-42 compatible
> > chip is used with an adapter which does not have I2C_CLASS_SPD set in
> > its flags ?
> >
> > > Alternative is to replace the SPD w HWMON class, but that carries
> > > risk for existing usage.
> > Yes, the driver would stop working on adapters which only have I2C_CLASS_SPD
> > set. There are only two of those, but those two presumably _do_ have memory
> > modules connected.
> >
> > Guenter
> >
> > > Signed-off-by: Alison Schofield <amsfield22@xxxxxxxxx>
> > > Cc: Daniel Baluta <daniel.baluta@xxxxxxxxx>
> > > ---
> > >   drivers/hwmon/jc42.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/hwmon/jc42.c b/drivers/hwmon/jc42.c
> > > index 9887d32..1537ba0 100644
> > > --- a/drivers/hwmon/jc42.c
> > > +++ b/drivers/hwmon/jc42.c
> > > @@ -538,7 +538,7 @@ static const struct i2c_device_id jc42_id[] = {
> > >   MODULE_DEVICE_TABLE(i2c, jc42_id);
> > >
> > >   static struct i2c_driver jc42_driver = {
> > > -	.class		= I2C_CLASS_SPD,
> > > +	.class		= I2C_CLASS_SPD | I2C_CLASS_HWMON,
> > >   	.driver = {
> > >   		.name	= "jc42",
> > >   		.pm = JC42_DEV_PM_OPS,
> --
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