linux-kernel - Re: [PATCH 2/5] clk: notifier handler for dynamic voltage scaling

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Date:	Sun, 10 Mar 2013 11:21:46 +0100
From:	Francesco Lavra <francescolavra.fl@...il.com>
To:	Mike Turquette <mturquette@...aro.org>
CC:	linux-kernel@...r.kernel.org, linaro-dev@...ts.linaro.org,
	linux-arm-kernel@...ts.infradead.org, patches@...aro.org
Subject: Re: [PATCH 2/5] clk: notifier handler for dynamic voltage scaling

On 02/28/2013 05:49 AM, Mike Turquette wrote:
> Dynamic voltage and frequency scaling (dvfs) is a common power saving
> technique in many of today's modern processors.  This patch introduces a
> common clk rate-change notifier handler which scales voltage
> appropriately whenever clk_set_rate is called on an affected clock.
> 
> There are three prerequisites to using this feature:
> 
> 1) the affected clocks must be using the common clk framework
> 2) voltage must be scaled using the regulator framework
> 3) clock frequency and regulator voltage values must be paired via the
> OPP library
> 
> If a platform or device meets these requirements then using the notifier
> handler is straightforward.  A struct device is used as the basis for
> performing initial look-ups for clocks via clk_get and regulators via
> regulator_get.  This means that notifiers are subscribed on a per-device
> basis and multiple devices can have notifiers subscribed to the same
> clock.  Put another way, the voltage chosen for a rail during a call to
> clk_set_rate is a function of the device, not the clock.
> 
> Signed-off-by: Mike Turquette <mturquette@...aro.org>
[...]
> +struct dvfs_info *dvfs_clk_notifier_register(struct dvfs_info_init *dii)
> +{
> +	struct dvfs_info *di;
> +	int ret = 0;
> +
> +	if (!dii)
> +		return ERR_PTR(-EINVAL);
> +
> +	di = kzalloc(sizeof(struct dvfs_info), GFP_KERNEL);
> +	if (!di)
> +		return ERR_PTR(-ENOMEM);
> +
> +	di->dev = dii->dev;
> +	di->clk = clk_get(di->dev, dii->con_id);
> +	if (IS_ERR(di->clk)) {
> +		ret = -ENOMEM;
> +		goto err;
> +	}
> +
> +	di->reg = regulator_get(di->dev, dii->reg_id);
> +	if (IS_ERR(di->reg)) {
> +		ret = -ENOMEM;
> +		goto err;
> +	}
> +
> +	di->tol = dii->tol;
> +	di->nb.notifier_call = dvfs_clk_notifier_handler;
> +
> +	ret = clk_notifier_register(di->clk, &di->nb);
> +
> +	if (ret)
> +		goto err;

Shouldn't regulator_put() and clk_put() be called in the error path?

> +
> +	return di;
> +
> +err:
> +	kfree(di);
> +	return ERR_PTR(ret);
> +}
> +EXPORT_SYMBOL_GPL(dvfs_clk_notifier_register);
> +
> +void dvfs_clk_notifier_unregister(struct dvfs_info *di)
> +{
> +	clk_notifier_unregister(di->clk, &di->nb);
> +	clk_put(di->clk);
> +	regulator_put(di->reg);
> +	kfree(di);
> +}
> +EXPORT_SYMBOL_GPL(dvfs_clk_notifier_unregister);

Regards,
Francesco
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