linux-kernel - Re: [PATCH 1/9] ARM i.MX51: Add ipu clock support

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Message-Id: <201012151640.03789.arnd@arndb.de>
Date:	Wed, 15 Dec 2010 16:40:03 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Sascha Hauer <s.hauer@...gutronix.de>,
	Arnaud Patard <arnaud.patard@...-net.org>,
	linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	"Zhang Lily-R58066" <r58066@...escale.com>
Subject: Re: [PATCH 1/9] ARM i.MX51: Add ipu clock support

On Thursday 09 December 2010, Sascha Hauer wrote:
> +static int clk_ipu_enable(struct clk *clk)
> +{
> +       u32 reg;
> +
> +       _clk_ccgr_enable(clk);
> +
> +       /* Enable handshake with IPU when certain clock rates are changed */
> +       reg = __raw_readl(MXC_CCM_CCDR);
> +       reg &= ~MXC_CCM_CCDR_IPU_HS_MASK;
> +       __raw_writel(reg, MXC_CCM_CCDR);
> +
> +       /* Enable handshake with IPU when LPM is entered */
> +       reg = __raw_readl(MXC_CCM_CLPCR);
> +       reg &= ~MXC_CCM_CLPCR_BYPASS_IPU_LPM_HS;
> +       __raw_writel(reg, MXC_CCM_CLPCR);
> +
> +       return 0;
> +}

Why __raw_readl?

The regular accessor function for I/O registers is readl, which handles
the access correctly with regard to atomicity, I/O ordering and byteorder.

	Arnd
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