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

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Date:   Tue, 13 Nov 2018 09:21:02 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Nicolin Chen <nicoleotsuka@...il.com>
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

On Mon, Nov 12, 2018 at 08:58:24PM -0800, Nicolin Chen wrote:
> 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.
> 

And you need to be able to do that with a sysfs attribute ?
Are you planning to have some code switching back and forth
between the modes ?

You'll need to provide a good rationale why this needs to be
runtime configurable.

Guenter

> 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