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. 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... -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!
