linux-kernel - Re: [PATCH 4/5] hwmon: (ina3221) Make sure data is ready after channel enabling

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Date:   Wed, 17 Oct 2018 18:04:18 -0700
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
Subject: Re: [PATCH 4/5] hwmon: (ina3221) Make sure data is ready after
 channel enabling

On Wed, Oct 17, 2018 at 02:17:14PM -0700, Guenter Roeck wrote:
> On Wed, Oct 17, 2018 at 01:53:48PM -0700, Nicolin Chen wrote:
> > Hello Guenter,
> > 
> > On Wed, Oct 17, 2018 at 09:55:43AM -0700, Guenter Roeck wrote:
> > > > @@ -676,6 +701,13 @@ static int __maybe_unused ina3221_resume(struct device *dev)
> > > >  	if (ret)
> > > >  		return ret;
> > > >  
> > > > +	/* Make sure data conversion is finished */
> > > > +	ret = ina3221_wait_for_data_if_active(ina);
> > > 
> > > This is quite expensive and would delay resume (and enable, for that matter).
> > > A less expensive solution would be to save the enable time here and in
> > > ina3221_write_enable(). ina3221_wait_for_data_if_active() can then be called
> > > from read functions and would wait if not enough time has expired.
> > > 
> > > 	if (time_before(...))
> > > 		usleep_range(missing wait time, missing_wait_time * 2);
> > > 
> > > or something like that. This could be done per channel or, to keep
> > > things simple, just using a single time for all channels.
> > 
> > I was thinking something that'd fit one-shot mode too so decided
> > to add a polling. But you are right. It does make sense to skip
> > polling until an actual read happens, though it also feels a bit
> > reasonable to me that putting a polling to the enabling routine.
> > 
> > The wait time would be sightly more complicated than the polling
> > actually, as it needs to involve total conversion time which may
> > vary depending on the number of enabled channels. I will see what
> > would be safer and easier and apply that in v2.
> > 
> It isn't that complex; we have done it in other drivers. It is less
> costly and has less overhead than extra i2c read operation(s).

OK. Will follow them in v2.

Thanks
Nicolin