From: Nick Crews <ncrews@chromium.org>
To: Dmitry Torokhov <dtor@google.com>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>,
Alessandro Zummo <a.zummo@towertech.it>,
linux-rtc@vger.kernel.org, lkml <linux-kernel@vger.kernel.org>,
Pavel Machek <pavel@ucw.cz>,
Enric Balletbo i Serra <enric.balletbo@collabora.com>,
Benson Leung <bleung@chromium.org>,
Duncan Laurie <dlaurie@chromium.org>,
Daniel Kurtz <djkurtz@chromium.org>
Subject: Re: [PATCH v3] rtc: wilco-ec: Handle reading invalid times
Date: Thu, 3 Oct 2019 14:37:31 -0600 [thread overview]
Message-ID: <CAHX4x84a1HpUvSJ6XeopJQuMZEM-Af_No2nHhi8q62eB+ZXxmA@mail.gmail.com> (raw)
In-Reply-To: <CAE_wzQ9AodXUEANpDEQM+VYMVuxWmLoF0_1k-m5HdAfx+=01-A@mail.gmail.com>
On Wed, Oct 2, 2019 at 9:20 AM Dmitry Torokhov <dtor@google.com> wrote:
>
> On Wed, Oct 2, 2019 at 3:32 AM Alexandre Belloni
> <alexandre.belloni@bootlin.com> wrote:
> >
> > On 01/10/2019 13:42:24-0700, Dmitry Torokhov wrote:
> > > On Tue, Oct 1, 2019 at 12:53 PM Alexandre Belloni
> > > <alexandre.belloni@bootlin.com> wrote:
> > > >
> > > > Hi Nick,
> > > >
> > > > On 25/09/2019 14:32:09-0600, Nick Crews wrote:
> > > > > If the RTC HW returns an invalid time, the rtc_year_days()
> > > > > call would crash. This patch adds error logging in this
> > > > > situation, and removes the tm_yday and tm_wday calculations.
> > > > > These fields should not be relied upon by userspace
> > > > > according to man rtc, and thus we don't need to calculate
> > > > > them.
> > > > >
> > > > > Signed-off-by: Nick Crews <ncrews@chromium.org>
> > > > > ---
> > > > > drivers/rtc/rtc-wilco-ec.c | 13 +++++++++----
> > > > > 1 file changed, 9 insertions(+), 4 deletions(-)
> > > > >
> > > > > diff --git a/drivers/rtc/rtc-wilco-ec.c b/drivers/rtc/rtc-wilco-ec.c
> > > > > index 8ad4c4e6d557..53da355d996a 100644
> > > > > --- a/drivers/rtc/rtc-wilco-ec.c
> > > > > +++ b/drivers/rtc/rtc-wilco-ec.c
> > > > > @@ -110,10 +110,15 @@ static int wilco_ec_rtc_read(struct device *dev, struct rtc_time *tm)
> > > > > tm->tm_mday = rtc.day;
> > > > > tm->tm_mon = rtc.month - 1;
> > > > > tm->tm_year = rtc.year + (rtc.century * 100) - 1900;
> > > > > - tm->tm_yday = rtc_year_days(tm->tm_mday, tm->tm_mon, tm->tm_year);
> > > > > -
> > > > > - /* Don't compute day of week, we don't need it. */
> > > > > - tm->tm_wday = -1;
> > > > > + /* Ignore other tm fields, man rtc says userspace shouldn't use them. */
> > > > > +
> > > > > + if (rtc_valid_tm(tm)) {
> > > > > + dev_err(dev,
> > > > > + "Time from RTC is invalid: second=%u, minute=%u, hour=%u, day=%u, month=%u, year=%u, century=%u",
> > > > > + rtc.second, rtc.minute, rtc.hour, rtc.day, rtc.month,
> > > > > + rtc.year, rtc.century);
> > > >
> > > > Do you mind using %ptR? At this point you already filled the tm struct
> > > > anyway and if you print century separately, you can infer tm_year.
> > >
> > > I do not think this is a good idea: we have just established that tm
> > > does not contain valid data. Does %ptR guarantee that it handles junk
> > > better than, let's say, rtc_year_days(), and does not crash when
> > > presented with garbage?
> > >
> >
> > It is safe to use. You can also use %ptRr if you want to ensure no
> > extra operations are done on the value before printing them out.
>
> OK, I'll keeo this in mind then.
I will resend this using %ptRr, chromium is using 4.19 so I didn't see
that this was added.
>
> >
> > I'm still not convinced it is useful to have an error in dmesg when the
> > time is invalid, as long as userspace knows it is invalid. What is the
> > course of action for the end user when that happens?
>
> Report it, or, in our case, we will see it in the feedback logs.
> However I do agree that it is not the best option, even if we report
> error to userspace I am not sure if it will handle it properly. What
> userspace is supposed to do when presented with -EIO or similar?
Yes, we will be able to see this in feedback logs, which would be valuable.
>
> Nick, do we know the root cause of the EC/RTC reporting invalid time?
No, I haven't really looked into it deeply. It's not limited to the RTC
interface though, it's a problem with the EC or EC communication
in general, as I've noticed similar occasional errors with the other EC
drivers.
>
> Thanks,
> Dmitry
prev parent reply other threads:[~2019-10-03 20:37 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-25 20:32 [PATCH v3] rtc: wilco-ec: Handle reading invalid times Nick Crews
2019-09-25 20:51 ` Dmitry Torokhov
2019-10-01 19:53 ` Alexandre Belloni
2019-10-01 20:42 ` Dmitry Torokhov
2019-10-02 10:32 ` Alexandre Belloni
2019-10-02 15:20 ` Dmitry Torokhov
2019-10-02 15:34 ` Alexandre Belloni
2019-10-03 20:37 ` Nick Crews [this message]
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