linux-kernel - Re: [PATCH 2/2] hwmon: ina3221: Add enable sysfs nodes

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Date:   Wed, 26 Sep 2018 11:02:44 -0700
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     jdelvare@...e.com, corbet@....net, afd@...com,
        linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH 2/2] hwmon: ina3221: Add enable sysfs nodes

On Wed, Sep 26, 2018 at 06:06:32AM -0700, Guenter Roeck wrote:
> On 09/25/2018 11:42 PM, Nicolin Chen wrote:
> > The inX_enable interface allows user space to enable or disable
> > the corresponding channel. Meanwhile, according to hwmon ABI, a
> > disabled channel/sensor should return -ENODATA as a read result.
> > 
> > However, there're configurable nodes sharing the same __show()
> > functions. So this change also adds to check if the attribute is
> > read-only to make sure it's not reading a configuration but the
> > sensor data.
 
> One necessary high level change I don't see below: With this change,
> we should no longer drop a channel entirely if it is disabled from
> devicetree. All channels should be visible but report -ENODATA if
> disabled. In other words, it should be possible for the 'enable' flag
> to override settings in DT.

Hmm...I don't feel so convinced here. The status in DT binding isn't
exactly a setting but a physical status: if a hardware design leaves
a channel to be disconnected, I don't really see a point in enabling
it in the runtime. Or maybe you can shed some light on it?

Meanwhile, I believe the enable nodes are necessary in either way as
users could decide to disable the connected channels, based on their
use cases, to save power.

Thanks
Nicolin