linux-kernel - Re: [PATCH v2 1/2] usb: phy: add a new driver for usb3 phy

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Date:	Thu, 27 Sep 2012 15:18:38 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Kishon Vijay Abraham I <kishon@...com>
Cc:	grant.likely@...retlab.ca, rob.herring@...xeda.com,
	rob@...dley.net, linux-usb@...r.kernel.org,
	linux-omap@...r.kernel.org, devicetree-discuss@...ts.ozlabs.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, Felipe Balbi <balbi@...com>,
	Moiz Sonasath <m-sonasath@...com>
Subject: Re: [PATCH v2 1/2] usb: phy: add a new driver for usb3 phy

On Thu, Sep 27, 2012 at 07:34:07PM +0530, Kishon Vijay Abraham I wrote:
> +static int omap5_usb_phy_power(struct omap_usb *phy, bool on)
> +{
> +	u32 val;
> +	unsigned long rate;
> +	struct clk *sys_clk;
> +
> +	sys_clk = clk_get(NULL, "sys_clkin");
> +	if (IS_ERR(sys_clk)) {
> +		pr_err("%s: unable to get sys_clkin\n", __func__);
> +		return -EINVAL;
> +	}
> +
> +	rate = clk_get_rate(sys_clk);
> +	rate = rate/1000000;
> +	clk_put(sys_clk);

Actually, you're supposed to hold on to the struct clk all the time your
driver is making use of that - you're not supposed to drop it.

That has several advantages: if clk_get() fails, then you're failing
earlier on (when the driver is being probed) and when some event occurs.
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