linux-kernel - Re: [PATCH v2] ARM: dts: vfxxx: Add iio_hwmon node for ADC temperature channel

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Date:	Mon, 15 Feb 2016 10:12:15 +0530
From:	maitysanchayan@...il.com
To:	Shawn Guo <shawnguo@...nel.org>
Cc:	stefan@...er.ch, linux-arm-kernel@...ts.infradead.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	jdelvare@...e.com, linux@...ck-us.net, lm-sensors@...sensors.org
Subject: Re: [PATCH v2] ARM: dts: vfxxx: Add iio_hwmon node for ADC
 temperature channel

Hello Shawn,

On 16-02-14 16:33:49, Shawn Guo wrote:
> On Fri, Feb 12, 2016 at 05:53:00PM +0530, Sanchayan Maity wrote:
> > Add iio_hwmon node to expose the temperature channel on Vybrid as
> > hardware monitor device using the iio_hwmon driver.
> > 
> > Signed-off-by: Sanchayan Maity <maitysanchayan@...il.com>
> > ---
> > 
> > Hello,
> > 
> > The first version of the patch was send quite a while ago.
> > https://lkml.org/lkml/2015/9/16/932
> > 
> > Shawn you had requested that hyphen rather than underscore should
> > be used in node name. I looked into that.
> > 
> > The iio_hwmon driver calls hwmon_device register_with_groups inside
> > hwmon.c and this
> > http://lxr.free-electrons.com/source/drivers/hwmon/hwmon.c#L103
> > 
> > does not allow hyphen in hwmon name attribute. I was not aware of
> > this but while trying to test the change, the device probe failed
> > with EINVAL. I think we should stick to the existing use of the
> > bindings or we need to change the hwmon code as well along with the
> > existing device tree files and binding documentation.
> 
> I disagree.
> 
> If hyphen is invalid to be part of hwmon name attribute, the following
> code in iio_hwmon_probe() is plain wrong, because hyphen is very valid
> to be part of node names in device tree.
> 
>         if (dev->of_node && dev->of_node->name)
>                 name = dev->of_node->name;

@Shawn
I agree with what you state here, however as you can see the hwmon_device_
register_with_groups does check for hypen with strpbrk and returns EINVAL.
Changing to hyphen instead of currently present underscore in iio_hwmon
node name causes probe failure.

If the node name needs to have hyphen, then the check for hyphen as an invalid
character in hwmon name attribute needs to be changed. I am CC'ing the hwmon
subsystem maintainers Jean Delvare ands Guenter Roeck as well as hwmon list to
check.

@Jean & Guenter
Can you please comment if the change to hwmon_device_register_with_groups
to accept hyphen as a valid character in hwmon name attribute will be acceptable?
Sorry if this is sudden andfor bringing you late into the discussion Jean and
Guenter.

Thanks & Regards,
Sanchayan.

> 
> Shawn
> 
> > 
> > Changes since v1:
> > 1. Expose ADC1 temperature channel as well
> > 2. Move the entry outside of the aips1 bus node
> > 
> > Best Regards,
> > Sanchayan Maity.
> > ---
> >  arch/arm/boot/dts/vfxxx.dtsi | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/arch/arm/boot/dts/vfxxx.dtsi b/arch/arm/boot/dts/vfxxx.dtsi
> > index a5f07e3..8ed8e47 100644
> > --- a/arch/arm/boot/dts/vfxxx.dtsi
> > +++ b/arch/arm/boot/dts/vfxxx.dtsi
> > @@ -673,5 +673,10 @@
> >  				status = "disabled";
> >  			};
> >  		};
> > +
> > +		iio_hwmon {
> > +			compatible = "iio-hwmon";
> > +			io-channels = <&adc0 16>, <&adc1 16>;
> > +		};
> >  	};
> >  };
> > -- 
> > 2.7.1
> > 
> >