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

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Message-ID: <20190417201234.GA6223@roeck-us.net>
Date:   Wed, 17 Apr 2019 13:12:34 -0700
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 voltage conversion time settings

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.

Guenter