lkml.org 
[lkml]   [2020]   [Jul]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v2 1/3] dt-bindings: rtc: pcf8523: add DSM pm option for battery switch-over
On 27/07/2020 16:24:39+0100, Russell King - ARM Linux admin wrote:
> On Mon, Jul 27, 2020 at 04:49:38PM +0200, Alexandre Belloni wrote:
> > On 27/07/2020 10:45:53+0100, Russell King - ARM Linux admin wrote:
> > > > This is but this shouldn't be a DT property as it has to be changed
> > > > dynamically. I'm working on an ioctl interface to change this
> > > > configuration.
> > >
> > > Why does it need to be changed dynamically? If the hardware components
> > > are not fitted to allow the RTC to be safely used without DSM, then
> > > why should userspace be able to disable DSM?
> >
> > For RTCs with a standby mode, you want to be able to return to standby
> > mode.
> >
> > That would happen for example after factory flashing in that common use
> > case:
> > - the board is manufactured
> > - Vbackup is installed, the RTC switches to standby mode
> > - the board is then booted to flash a system, Vprimary is now present,
> > the RTC switches to DSM.
> >
> > At this point, if the board is simply shut down, the RTC will start
> > draining Vbackup before leaving the factory. Instead, we want to be able
> > to return to standby mode until the final user switches the product on
> > for the first time.
>
> I don't think you're understanding what's going on with this proposed
> patch. The cubox-i does work today, and the RTC does survive most
> power-downs. There are situations where it doesn't.
>
> So, let's take your process above.
>
> - the board is manufactured
> - Vbackup is installed, the RTC switches to standby mode
> - the board is then booted to flash a system, Vprimary is now present
> - the board is powered down. the RTC _might_ switch over to battery
> if it notices the power failure in time, or it might not. A random
> sample of units leaving the factory have the RTC in standby mode.
> Others are draining the battery.
>
> I'm not saying what you propose isn't a good idea. I'm questioning
> why we should expose this in the generic kernel on platforms where
> it's likely to end up with the RTC being corrupted.
>

Note that I didn't say we should expose settings that are not working
but it is a different discussion. I was explaining why we need to be
able to change it dynamically.

> Now, I question your idea that units should leave the factory without
> the RTC being programmed. We know that lovely systemd goes utterly
> bonkers if the system time is beyond INT_MAX. If the RTC leaves
> standby mode containing a date which we translate beyond INT_MAX,
> systemd will refuse to boot the system, and the user will have no
> way to set the correct time. The user returns the device to the
> supplier as faulty...

This is doesn't happen since v4.17.

--
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

\
 
 \ /
  Last update: 2020-07-27 17:42    [W:1.838 / U:0.388 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site