linux-kernel - Re: [PATCH] hwmon (ina3221) Add single-shot mode support

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Date:   Mon, 12 Nov 2018 20:58:24 -0800
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     jdelvare@...e.com, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org, corbet@....net,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH] hwmon (ina3221) Add single-shot mode support

Hi Guenter,

On Mon, Nov 12, 2018 at 08:32:48PM -0800, Guenter Roeck wrote:
> On Mon, Nov 12, 2018 at 08:23:53PM -0800, Nicolin Chen wrote:
> > INA3221 supports both continuous and single-shot modes. When
> > running in the continuous mode, it keeps measuring the inputs
> > and converting them to the data register even if there are no
> > users reading the data out. In this use case, this could be a
> > power waste.
> > 
> > So this patch adds a single-shot mode support so that ina3221
> > could do measurement and conversion only if users trigger it,
> > depending on the use case where it only needs to poll data in
> > a lower frequency.
> > 
> > The change also exposes "mode" and "available_modes" nodes to
> > allow users to switch between two operating modes.
> > 
> Lots and lots of complexity for little gain. Sorry, I don't see
> the point of this change.

The chip is causing considerable power waste on battery-powered
devices so we typically use it running in the single-shot mode.

Although the chip now can be powered down, but we still need to
occasionally poll it for power measurement and critical alerts,
so single-shot mode is the best choice for us, considering that
the power-down-and-up routine would be way heavier.

I could understand that you don't really like it, but it's some
feature that we truly need. Do you have any suggestion to write
the code that can make it more convincing to you?

Thanks
Nicolin