RE: [PATCH v2] alarmtimer: Fix rebind failure

[Biju Das <biju.das.jz@bp.renesas.com>]

Hi Thomas Gleixner,

> Subject: RE: [PATCH v2] alarmtimer: Fix rebind failure
> 
> On Mon, Oct 09 2023 at 17:02, Biju Das wrote:
> >> On Mon, Oct 09 2023 at 15:30, Biju Das wrote:
> >> > You mean we should update[1] (charger-manager driver)as it is the
> >> > one using alarmtimer_get_rtcdev()??
> >>
> >> # git grep -c alarmtimer_get_rtcdev
> >> drivers/power/supply/charger-manager.c:1
> >> include/linux/alarmtimer.h:2
> >> kernel/time/alarmtimer.c:10
> >
> > kernel/time/alarmtimer.c has alarmtimer_get_rtcdev()check everywhere,
> > that is missing in charger-manager.c. I will add the same, is it ok?
> 
> The code does in the init function:
> 
>       if (alarmtimer_get_rtcdev()) {
>          ....
>       }
> 
> IOW, charger-manager.c expects that alarm is working when
> alarmtimer_get_rtcdev() returns non NULL at init. So ripping the RTC device
> out under it is going to result in a disfunctional driver. I'm not
> convinced that you can fix this by sprinkling a ton of checks around the
> code.
> 
> But that's not the worst of it. The alarmtimer infrastructure is generally
> not designed for device/module removal. Why?
> 
> The posix timer interface is fundamentally expecting that an armed alarm
> timer is actually functional. The fact that the class interface does not
> have a remove_dev callback is not an oversight and holding a reference on
> the module and a reference on the device is intended to ensure that the
> device cannot vanish.

Thanks for the explanation, I am not aware we should not remove RTC device. 

> 
> The changelog lacks any form of explanation why this is required and how
> removal of the registered RTC device is actually possible. Neither does it
> provide any analysis why this cannot result in malfunction.

RTC driver is defined as a module, so I was testing
remove/unbind followed by install/bind on RTC driver to check
any resource leakage and found that device is not working properly.

As you mentioned above, we should not remove RTC driver. So I would like to drop this patch.

Is there any place we can document this to avoid another person doing same mistake?

Cheers,
Biju