Date: Fri, 28 Nov 2014 00:16:56 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: Xunlei Pang <pang.xunlei@linaro.org>
cc: linux-kernel@vger.kernel.org, rtc-linux@googlegroups.com,
        Alessandro Zummo <a.zummo@towertech.it>,
        Sven Schnelle <svens@stackframe.org>,
        John Stultz <john.stultz@linaro.org>,
        Arnd Bergmann <arnd.bergmann@linaro.org>
Subject: Re: [RFC PATCH 3/4] rtc/lib: Provide interfaces to map between 32bit
 hardware and 64bit time
In-Reply-To: <1417089760-26848-4-git-send-email-pang.xunlei@linaro.org>
Message-ID: <alpine.DEB.2.11.1411280005500.3961@nanos>
References: <1417089760-26848-1-git-send-email-pang.xunlei@linaro.org> <1417089760-26848-4-git-send-email-pang.xunlei@linaro.org>
User-Agent: Alpine 2.11 (DEB 23 2013-08-11)
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Sender: linux-kernel-owner@vger.kernel.org

On Thu, 27 Nov 2014, Xunlei Pang wrote:
> +/* Rtc epoch year, can be overrided by command line */
> +static unsigned int rtc_epoch = 1970;
> +time64_t rtc_epoch_secs_since_1970;
> +
> +static int __init
> +set_rtc_epoch(char *str)

One line please

> +{
> +	unsigned int epoch;
> +
> +	if (kstrtou32(str, 0, &epoch) != 0) {
> +		printk(KERN_WARNING "Invalid setup epoch %u!\n", epoch);

Sure that makes a lot of sense to print epoch if the string conversion
failed. epoch is going to be either uninitialized stack value or 0
depending on the kstrtou32 implementation.

> +	if (rtc_epoch < 1970)
> +		printk(KERN_WARNING "Epoch %u is smaller than 1970!\n", epoch);

  pr_warn() ....

+__setup("rtc_epoch=", set_rtc_epoch);

Not documented in Documentation/kernel-parameters.txt ...

>  /*
> + * Convert seconds since rtc epoch to seconds since Unix epoch.
> + */
> +time64_t rtc_hw32_to_time64(u32 hwtime)
> +{
> +	return (rtc_epoch_secs_since_1970 + hwtime);
> +}
> +EXPORT_SYMBOL_GPL(rtc_hw32_to_time64);

So we need a exported function to add a global variable and a function
argument? inline ?

> +/*
> + * Convert seconds since Unix epoch to seconds since rtc epoch.
> + */
> +int rtc_time64_to_hw32(time64_t time, u32 *hwtime)
> +{
> +	/* time must be after rtc epoch */
> +	if (time < rtc_epoch_secs_since_1970)
> +		return -EINVAL;
> +
> +	/* rtc epoch may be too small? */
> +	if (time - rtc_epoch_secs_since_1970 > UINT_MAX)
> +		return -EOVERFLOW;

And what's the caller supposed to do with that information?

> +	*hwtime = time - rtc_epoch_secs_since_1970;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(rtc_time64_to_hw32);

How is that going to be useful w/o a mechanism to adjust the epoch
offset at runtime by any means?

Thanks,

	tglx


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/