linux-kernel - Re: [PATCH v2 2/2] rtc: rtc-pic32: Add PIC32 real time clock driver

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Date:	Thu, 25 Feb 2016 09:23:55 -0700
From:	Joshua Henderson <joshua.henderson@...rochip.com>
To:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
CC:	<devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	<rtc-linux@...glegroups.com>
Subject: Re: [PATCH v2 2/2] rtc: rtc-pic32: Add PIC32 real time clock driver

On 02/24/2016 03:25 PM, Alexandre Belloni wrote:
> Hi,
> 
> On 19/02/2016 at 11:09:45 -0700, Joshua Henderson wrote :
>> +static int pic32_rtc_gettime(struct device *dev, struct rtc_time *rtc_tm)
>> +{
>> +	struct pic32_rtc_dev *pdata = dev_get_drvdata(dev);
>> +	void __iomem *base = pdata->reg_base;
>> +	unsigned int tries = 0;
>> +
>> +	clk_enable(pdata->clk);
>> +
>> +	do {
>> +		rtc_tm->tm_hour = readb(base + PIC32_RTCHOUR);
>> +		rtc_tm->tm_min = readb(base + PIC32_RTCMIN);
>> +		rtc_tm->tm_mon  = readb(base + PIC32_RTCMON);
>> +		rtc_tm->tm_mday = readb(base + PIC32_RTCDAY);
>> +		rtc_tm->tm_year = readb(base + PIC32_RTCYEAR);
>> +		rtc_tm->tm_sec  = readb(base + PIC32_RTCSEC);
>> +
>> +		/*
>> +		 * The only way to work out whether the system was mid-update
>> +		 * when we read it is to check the second counter, and if it
>> +		 * is zero, then we re-try the entire read.
>> +		 */
>> +		tries = 1;
>> +	} while (rtc_tm->tm_sec == 0 && tries < 2);
>> +
> 
> This doesn't seem right. It will wait up to a second as tries will
> always be less than 2, this is probably not what you want.

Dang good catch.  When fixed, it will work as expected:

# hwclock
tries 1
Sun Oct 17 19:23:59 2010  0.000000 seconds
# hwclock
tries 1
tries 2
Sun Oct 17 19:24:00 2010  0.000000 seconds
# hwclock
tries 1
Sun Oct 17 19:24:01 2010  0.000000 seconds

Josh