linux-kernel - RE: [PATCH v2 5/5] rtc: add mxc driver for i.MX53 SRTC

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Message-ID: <3BB206AB2B1BD448954845CE6FF69A8E01CB531D7C@NT-Mail07.beckhoff.com>
Date:   Wed, 6 Dec 2017 09:28:09 +0000
From:   Patrick Brünn <P.Bruenn@...khoff.com>
To:     Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
        Sascha Hauer <s.hauer@...gutronix.de>
CC:     linux-kernel-dev <linux-kernel-dev@...khoff.com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <kernel@...gutronix.de>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Mark Rutland <mark.rutland@....com>,
        "open list:REAL TIME CLOCK (RTC) SUBSYSTEM" 
        <linux-rtc@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, Juergen Borleis <jbe@...gutronix.de>,
        open list <linux-kernel@...r.kernel.org>,
        Russell King <linux@...linux.org.uk>,
        "Noel Vellemans" <Noel.Vellemans@...ionbms.com>,
        Rob Herring <robh+dt@...nel.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Fabio Estevam <fabio.estevam@....com>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        Lothar Waßmann <LW@...O-electronics.de>
Subject: RE: [PATCH v2 5/5] rtc: add mxc driver for i.MX53 SRTC

>From: Alexandre Belloni [mailto:alexandre.belloni@...e-electrons.com]
>Sent: Mittwoch, 6. Dezember 2017 09:58
>On 06/12/2017 at 09:36:18 +0100, Sascha Hauer wrote:
>> > +/*
>> > + * This function updates the RTC alarm registers and then clears all the
>> > + * interrupt status bits.
>> > + * The caller should hold the pdata->lock
>> > + *
>> > + * @param  alrm         the new alarm value to be updated in the RTC
>> > + *
>> > + * @return  0 if successful; non-zero otherwise.
>> > + */
>> > +static int mxc_rtc_write_alarm_locked(struct mxc_rtc_data *const pdata,
>> > +                                struct rtc_time *alarm_tm)
>> > +{
>> > +  void __iomem *const ioaddr = pdata->ioaddr;
>> > +  unsigned long time;
>> > +
>> > +  rtc_tm_to_time(alarm_tm, &time);
>> > +
>> > +  if (time > U32_MAX) {
>> > +          pr_err("Hopefully I am out of service by then :-(\n");
>> > +          return -EINVAL;
>> > +  }
>>
>> This will never happen as on your target hardware unsigned long is a
>> 32bit type. Not sure what is best to do here. Maybe you should test
>> the return value of rtc_tm_to_time. ATM it returns 0 unconditionally,
>> but rtc_tm_to_time could detect when the input time doesn't fit into
>> its return type and return an error in this case.
>> Also I just realized that it's unsigned and only overflows in the year
>> 2106. I'm most likely dead then so I don't care that much ;)
>>
>
>One solution is to use the 64bit version instead so it doesn't overflow.
>This makes the time > U32_MAX work.
>Also, I'll send (hopefully soon) a series adding proper range checking
>for the whole RTC subsystem. And yes, it not urgent as I don't think I
>will care so much in 2106 too ;)
>
I just noticed that in mxc_rtc_set_time() I am using the 64bit version.
After thinking a while about this issue, I think the 64bit version is better
suited for my use case. It makes explicitly clear that I need to push the
time into a 32bit hw register and "unsigned long" is just by accident the
correct size for me.

>> > +/*
>> > + * This function reads the current RTC time into tm in Gregorian date.
>> > + *
>> > + * @param  tm           contains the RTC time value upon return
>> > + *
>> > + * @return  0 if successful; non-zero otherwise.
>> > + */
>> > +static int mxc_rtc_read_time(struct device *dev, struct rtc_time *tm)
>> > +{
>> > +  struct mxc_rtc_data *pdata = dev_get_drvdata(dev);
>> > +  time_t now;
>> > +  int ret = mxc_rtc_lock(pdata);
>> > +
>> > +  if (ret)
>> > +          return ret;
>> > +
>> > +  now = readl(pdata->ioaddr + SRTC_LPSCMR);
>> > +  rtc_time_to_tm(now, tm);
>> > +  ret = rtc_valid_tm(tm);
>
>This check is useless for two reasons: you know that rtc_time_to_tm will
>generate a valid tm and the core always checks the tm anyway.
I will remove this with the next version

Thanks for your time and help,
Patrick

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