linux-kernel - Re: [STLinux Kernel] [PATCH v3 7/8] rtc: st: add new driver for ST's LPC RTC

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Date:	Mon, 23 Feb 2015 10:12:23 +0000
From:	Peter Griffin <peter.griffin@...aro.org>
To:	Lee Jones <lee.jones@...aro.org>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org, kernel@...inux.com,
	rtc-linux@...glegroups.com, wim@...ana.be, linux@...ck-us.net,
	linux-watchdog@...r.kernel.org
Subject: Re: [STLinux Kernel] [PATCH v3 7/8] rtc: st: add new driver for ST's
 LPC RTC

Hi Lee,

On Wed, 18 Feb 2015, Lee Jones wrote:

> ST's Low Power Controller (LPC) controls two devices; watchdog and RTC.
> Only one of the devices can be used at any one time.  This is enforced
> by the correlating MFD driver.  This portion of the driver-set controls
> the Real Time Clock.

<snip>

> +{
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&rtc->lock, flags);
> +
> +	writel(1, rtc->ioaddr + LPC_WDT_OFF);
> +
> +	writel(msb, rtc->ioaddr + LPC_LPA_MSB_OFF);
> +	writel(lsb, rtc->ioaddr + LPC_LPA_LSB_OFF);
> +	writel(1, rtc->ioaddr + LPC_LPA_START_OFF);
> +
> +	writel(0, rtc->ioaddr + LPC_WDT_OFF);

I think all the writel IO accessors in this driver can be replaced
with the *_relaxed variant. This will avoid the overhead of taking a
spinlock in the l2 outer cache part of writel.

<snip>

> +#ifdef CONFIG_PM_SLEEP
> +static int st_rtc_suspend(struct device *dev)
> +{
> +	struct st_rtc *rtc = dev_get_drvdata(dev);
> +
> +	if (device_may_wakeup(dev))
> +		return 0;
> +
> +	writel(1, rtc->ioaddr + LPC_WDT_OFF);
> +	writel(0, rtc->ioaddr + LPC_LPA_START_OFF);
> +	writel(0, rtc->ioaddr + LPC_WDT_OFF);

Is there a reason for not disabling the IP clock in suspend / resume functions?

regards,

Peter.
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