linux-kernel - Re: [PATCH] Fix LPC32XX's clock.c

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Message-ID: <20120128160011.GA15455@n2100.arm.linux.org.uk>
Date:	Sat, 28 Jan 2012 16:00:11 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Roland Stigge <stigge@...com.de>
Cc:	w.sang@...gutronix.de, grant.likely@...retlab.ca,
	linus.walleij@...aro.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix LPC32XX's clock.c

On Fri, Jan 27, 2012 at 03:17:48PM +0100, Roland Stigge wrote:
> @@ -382,30 +388,62 @@ static u32 local_clk_usbpll_setup(struct clk_pll_setup *pHCLKPllSetup)
>  static int local_usbpll_enable(struct clk *clk, int enable)
>  {
>  	u32 reg;
> -	int ret = -ENODEV;
> -	unsigned long timeout = 1 + msecs_to_jiffies(10);
> +	int ret = 0;
> +	unsigned long timeout = jiffies + msecs_to_jiffies(20);

...

> -		/* Wait for PLL lock */
> -		while ((timeout > jiffies) & (ret == -ENODEV)) {
> +		/*
> +		 * Enable PLL
> +		 */
> +		reg |= LPC32XX_CLKPWR_USBCTRL_PLL_PWRUP;
> +		__raw_writel(reg, LPC32XX_CLKPWR_USB_CTRL);
> +
> +		/*
> +		 * Wait for PLL to lock
> +		 */
> +		while ((timeout > jiffies) && (ret == -ENODEV)) {

This is buggy - it's waiting to go wrong when jiffies wraps.  You really
want to use time_before() or time_after() to make these comparisons, which
are safe against wrap-around.
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