Re: Bug#932845: TS-219 RTC issue with Debian Buster

["Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>]

Hello Alexandre,

On Thu, Jul 25, 2019 at 04:31:49PM +0200, Oliver Hartkopp wrote:
> On 24.07.19 09:07, Uwe Kleine-König wrote:
> > On Tue, Jul 23, 2019 at 10:28:18PM +0200, Oliver Hartkopp wrote:
> > > I'm running a TS-119P+ and a TS-219P II Qnap NAS with Debian Buster.
> > > Both are now running a linux-image-4.19.0-5-marvell kernel.
> > > 
> > > But since my update from Linux 4.9 (Stretch) to Linux 4.19 (Buster) the
> > > hardware clock of both boxes refuse to work.
> > > 
> > > After some digging in kernel sources and re-installing Linux 4.9 on my
> > > Buster setup it turns out, that a change in the kernel config causes the
> > > problem:
> > > 
> > > 4.19.0-5-marvell -> CONFIG_RTC_DRV_S35390A=m   (fails)
> > > 
> > > 4.9.0-4-marvell -> CONFIG_RTC_DRV_S35390A=y    (works)
> > > 
> > > See details and solving process at:
> > > 
> > > https://marc.info/?l=linux-arm-kernel&m=156390875629259&w=2
> > > 
> > > Can you please revert the Kernel config parts for the RTC in a way that the
> > > RTC drivers are built into the marvell-arch kernel again instead of building
> > > them as modules?
> > 
> > They were switched to modules because the kernel image got too big to
> > fit into the flash storage of some machines. I assume when we switch to
> > built-in again the resulting problem is the bigger one.
> 
> I don't know which is the bigger problem here.
> 
> When the rtc driver is built as module it can not be operated with the
> hwclock tool from the util-linux package due to the missing rtc UIE support.
> 
> You finally have no hardware clock on these machines and must wait for ntp
> to shift time and date (my system always starts in February until ntp fixes
> the time).

For me it's obvious what is the bigger problem. Either you don't have
the correct time until ntp fixes it up for you, or others cannot install
a kernel update and so run a vulnerable OS.

> Maybe this problem is only relevant for the S35390A and PCF8563 chip which
> both lack the UIE support needed by hwclock. Both have only alarm triggers
> in a minute accuracy according to the driver source code.

AFAIK the rtc framework should then emulate this event somehow.

> So CONFIG_RTC_DRV_S35390A=y and CONFIG_RTC_DRV_PCF8563=y should bring back
> the hw clocks on these machines.
> 
> I assume using hwclock without UIE trigger code will impact the accuracy.
> 
> > > As described in the referenced description the hwclock tool does not work on
> > > the machines.
> > 
> > I'm not sure yet if this is a problem in hwclock() or the s35390a
> > driver.
> 
> In detail it is hwclock together with rtc drivers not supporting UIE trigger
> with a 1 second resolution.

@abelloni: Do you can shed some light here, how it is supposed to work?
Is hwclock just doing it wrong with non-PC clocks, or is there a kernel
bug to fix?

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |