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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 14.04.2020 15:47, Alexandre Belloni wrote: > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe > > On 14/04/2020 12:13:46+0000, Claudiu.Beznea@microchip.com wrote: >> >> >> On 14.04.2020 14:16, Alexandre Belloni wrote: >>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe >>> >>> On 14/04/2020 08:42:08+0000, Claudiu.Beznea@microchip.com wrote: >>>>> Why would one use the RTT while the RTC is far superior? >>>> >>>> I didn't enabled this for a particular use case, but: couldn't this be used >>>> by some user that wants to generate multiple alarms? from multiple RTCs? >>>> >>> >>> I very much doubt that as Linux is able to properly multiplex alarms and >>> basically, the only one we are interested in is actually wakeup. >> >> I think you can use the wakealarm sysfs exported file to prepare an alarm >> and take user space actions based on that without being suspended. >> >>> >>>> Moreover, this IP's counter has the possibility of being clocked at 1Hz. >>>> Couldn't this minimize the power consumption while being in a power saving >>>> mode? >>>> >>> >>> And that 1Hz clock is coming from the RTC so using the RTC is >>> definitively consuming less power. >> >> Datasheet specifies this: "Configuring the RTPRES field value to 0x8000 >> (default value) corresponds to feeding the real-time counter with a >> >> 1Hz signal (if the slow clock is 32.768 kHz)." >> >> So, it is not the RTC, it is the slow clock divided by 32768. > > This is not what you described previously, I said this way: "this *IP's counter* has the possibility of being clocked at 1Hz" > using RTPRES means running > the RTT at 32kHz. This is exactly what happens with the RTC but you get > the added clock calibration circuitry that is probably not drawing to > much power but the added consumption of the configurable prescaler > versus the static prescaler of the RTC is probably similar. > > Using RTC1HZ would be driving the RTT at 1Hz. > >>> But this is very unlikely to happen because this would be limited to a >>> single board device tree instead of impact every sam9x60 based boards. >> >> Very unlikely but a having a patch with diff like this: >> >> +&gpbr { >> + status = "okay"; >> +}; >> + >> +&rtt { >> + atmel,rtt-rtc-time-reg = <&gpbr 0x0>; >> + status = "okay"; >> +}; >> + >> >> and reverting it may affect the other users of gpbr in sam9x60ek.dts. >> > > Again, this affects only sam9x60ek.dts instead of possibly multiple DTs > that may be out of tree. So the risk of doing that is null. Anyway... I'll merge it although I don't consider is the right way. > > -- > Alexandre Belloni, Bootlin > Embedded Linux and Kernel engineering > https://bootlin.com > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel