linux-kernel - Re: [PATCH v3 2/2] hwmon: ina3221: Read channel input source info from DT

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Date:   Sat, 22 Sep 2018 11:46:51 -0700
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     jdelvare@...e.com, robh+dt@...nel.org, mark.rutland@....com,
        corbet@....net, afd@...com, linux-hwmon@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v3 2/2] hwmon: ina3221: Read channel input source info
 from DT

> >This patch adds a new structure of input source specific
> >information including input source label, shunt resistor
> >value and its connection status. It exposes these labels
> >via sysfs and also disables those channels where there's
> >no input source being connected.
> >
> 
> I see you have decided to just display the disconnected channels.
> This is misleading, and I can not accept it. Please either use the
> is_visible callback to not display those channels at all, or have

I will add is_visible. I have almost finished it while waiting for
the v3's review comments. Will test it and include in the v4.

> the _input attribute of disabled channels return -ENODATA (see
> 'in[0-*]_enable' attribute in the ABI). If you implement the latter,
> I would suggest to also implement the _enable attribute.

I will also add one separate patch for in[0-*]_enable after these
two changes pass the review and get applied.

> As mentioned in patch 1, I can not accept an implicitly mandatory
> label attribute. The property defining the label attribute will
> have to be optional and well defined to ensure that it matches
> the ABI.

I replied this in the PATCH-1. Let's discuss this topic there.

> >+	/* Disable channels if their inputs are disconnected */
> >+	for (i = 0, mask = 0; i < INA3221_NUM_CHANNELS; i++) {
> >+		if (ina->inputs[i].disconnected)
> >+			mask |= INA3221_CONFIG_CHx_EN(i);
> >+	}
> 
> Consequently, you should also _enable_ channels which are not explicitly disabled.

The register has enabled all channels by default. So I felt it'd
be neat to have disabling code only. My v1 actually had enabling
part as well, but I can add it back if you think it'd be better.

> This can be tricky since you'll have to distinguish non-DT and DT configuration
> and retain the original configuration if no channel configuration data is available
> from devicetree.

I don't quite understand this comments. Would you please elaborate
it?

For non-DT configurations, input->disconnected is always false by
default unless someone adds config for it (through platform_data).
If regmap_update_bits only does disabling like this version does,
non-DT configurations will not get affected since mask = 0. Or if
we change it to do both enabling and disabling, regmap_update_bits
will still ignore since there's no register value changed, though
it won't really hurt even if regmap writes correct configurations
to the register.

For DT configurations (without channel input source defined), it's
like the same as non-DT configurations. As we have platforms only
enabled ina3221 via DT while they don't have this new DT binding,
the driver has to be backward compatible, so my change only sets
input->disconnected=true when a status="disabled" is present, i.e.
those platforms are treated as all channels getting enabled until
they update their DTs.

Thanks for the review
Nicolin