linux-kernel - Re: [PATCH V2 01/16] PM / OPP: get/put regulators from OPP core

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Date:	Mon, 1 Feb 2016 18:29:21 -0800
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Rafael Wysocki <rjw@...ysocki.net>, linaro-kernel@...ts.linaro.org,
	linux-pm@...r.kernel.org, nm@...com,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Len Brown <len.brown@...el.com>,
	open list <linux-kernel@...r.kernel.org>,
	Pavel Machek <pavel@....cz>, Viresh Kumar <vireshk@...nel.org>
Subject: Re: [PATCH V2 01/16] PM / OPP: get/put regulators from OPP core

On 01/28, Viresh Kumar wrote:
> +
> +/**
> + * dev_pm_opp_put_regulator() - Releases resources blocked for regulator
> + * @dev: Device for which regulator was set.
> + *
> + * Locking: The internal device_opp and opp structures are RCU protected.
> + * Hence this function internally uses RCU updater strategy with mutex locks
> + * to keep the integrity of the internal data structures. Callers should ensure
> + * that this function is *NOT* called under RCU protection or in contexts where
> + * mutex cannot be locked.
> + */
> +void dev_pm_opp_put_regulator(struct device *dev)
> +{
> +	struct device_opp *dev_opp;
> +
> +	mutex_lock(&dev_opp_list_lock);
> +
> +	/* Check for existing list for 'dev' first */
> +	dev_opp = _find_device_opp(dev);
> +	if (IS_ERR(dev_opp)) {
> +		dev_err(dev, "Failed to find dev_opp: %ld\n", PTR_ERR(dev_opp));
> +		goto unlock;
> +	}
> +
> +	if (IS_ERR_OR_NULL(dev_opp->regulator)) {
> +		dev_err(dev, "%s: Doesn't have regulator set\n", __func__);
> +		goto unlock;
> +	}
> +
> +	/* Make sure there are no concurrent readers while updating dev_opp */
> +	WARN_ON(!list_empty(&dev_opp->opp_list));
> +
> +	regulator_put(dev_opp->regulator);
> +	dev_opp->regulator = ERR_PTR(-EINVAL);
> +
> +	/* Try freeing device_opp if this was the last blocking resource */
> +	_remove_device_opp(dev_opp);
> +
> +unlock:
> +	mutex_unlock(&dev_opp_list_lock);
> +}
> +EXPORT_SYMBOL_GPL(dev_pm_opp_put_regulator);

I'm still lost why we need this API. When the OPP is torn down we
can call regulator_put there instead. The same style seems to be
done for supported hw, and prop_name, which doesn't make any
sense either. Just tear everything down when there aren't any
more OPPs in the table.

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