linux-kernel - Re: [PATCH] hwmon: (ina3221) Add voltage conversion time settings

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Date:   Wed, 17 Apr 2019 14:10:26 -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, corbet@....net,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH] hwmon: (ina3221) Add voltage conversion time settings

On Wed, Apr 17, 2019 at 01:12:34PM -0700, Guenter Roeck wrote:
> On Wed, Apr 17, 2019 at 12:48:18PM -0700, Nicolin Chen wrote:
> > On Wed, Apr 17, 2019 at 11:39:49AM -0700, Nicolin Chen wrote:
> > 
> > > > Thinking about it ... does it even make sense to cache reg_config twice,
> > > > or would it be better to just update the local copy and use regmap_write()
> > > > to send it to the chip ?
> > > 
> > > I remember the reason of adding the read-back was to prevent race
> > > condition. But now we have mutex protections for all sysfs nodes,
> > > maybe it's not necessary anymore. I will read the code carefully
> > > and see if it's safe to remove it -- will do in a separate patch.
> > 
> > I just recalled a second thought for the reason why I left them
> > there as it'd logically require a copy to restore upon failure
> > of regmap_write, that might not look so neat as the read-back:
> > 
> > 	old_config = reg_config;
> > 	reg_config &= mask;
> > 	reg_config |= val;
> > 	ret = regmap_write(reg_config);
> > 	if (ret) {
> > 		reg_config = old_config;
> > 		return ret;
> > 	}
> 
> 	reg = (reg_config & mask) | val;
> 	ret = regmap_write(reg);
> 	if (ret) 
> 		return ret;
> 	reg_config = reg;
> 
> doesn't look that bad to me, and is much less costly.

Okay. Will submit a change. Thanks