From: Dmitry Torokhov <dtor@google.com>
To: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: Nick Crews <ncrews@chromium.org>,
Alessandro Zummo <a.zummo@towertech.it>,
linux-rtc@vger.kernel.org, lkml <linux-kernel@vger.kernel.org>,
Pavel Machek <pavel@ucw.cz>,
enric.balletbo@collabora.com, Benson Leung <bleung@chromium.org>,
dlaurie@chromium.org, Daniel Kurtz <djkurtz@chromium.org>
Subject: Re: [PATCH v3] rtc: wilco-ec: Handle reading invalid times
Date: Wed, 2 Oct 2019 08:20:34 -0700 [thread overview]
Message-ID: <CAE_wzQ9AodXUEANpDEQM+VYMVuxWmLoF0_1k-m5HdAfx+=01-A@mail.gmail.com> (raw)
In-Reply-To: <20191002103236.GM4106@piout.net>
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'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?
Nick, do we know the root cause of the EC/RTC reporting invalid time?
Thanks,
Dmitry
next prev parent reply other threads:[~2019-10-02 15:20 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 [this message]
2019-10-02 15:34 ` Alexandre Belloni
2019-10-03 20:37 ` Nick Crews
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAE_wzQ9AodXUEANpDEQM+VYMVuxWmLoF0_1k-m5HdAfx+=01-A@mail.gmail.com' \
--to=dtor@google.com \
--cc=a.zummo@towertech.it \
--cc=alexandre.belloni@bootlin.com \
--cc=bleung@chromium.org \
--cc=djkurtz@chromium.org \
--cc=dlaurie@chromium.org \
--cc=enric.balletbo@collabora.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-rtc@vger.kernel.org \
--cc=ncrews@chromium.org \
--cc=pavel@ucw.cz \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).