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    SubjectRe: [PATCH 4/5] ARM: dts: sam9x60: add rtt
    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.

    > 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.

    > >
    > >>>
    > >>> In any case, this diff should be merge with the other at91-sam9x60ek.dts
    > >>> change instead of being with the dtsi change.
    > >>
    > >> The changes in this patch are related to enabling the RTT. The other dts
    > >> change is related to enabling gpbr. The RTT uses that enabled gpbr -> one
    > >> change per patch.
    > >>
    > >> If you still want to merge then, I'll do it, but then it becomes mixed.
    > >>
    > >
    > > This patch is already mixing add the gpbr in sam9x60ek and add the node
    > > in sam9x60.dtsi which is worse.
    >
    > This patch is like this:
    >
    > diff --git a/arch/arm/boot/dts/at91-sam9x60ek.dts
    > b/arch/arm/boot/dts/at91-sam9x60ek.dts
    > index ab3d2d9a420a..4020e79a958e 100644
    > --- a/arch/arm/boot/dts/at91-sam9x60ek.dts
    > +++ b/arch/arm/boot/dts/at91-sam9x60ek.dts
    > @@ -617,6 +617,11 @@
    > };
    > };
    >
    > +&rtt {
    > + atmel,rtt-rtc-time-reg = <&gpbr 0x0>;
    > + status = "okay";
    > +};
    > +
    > &shutdown_controller {
    > atmel,shdwc-debouncer = <976>;
    > status = "okay";
    > diff --git a/arch/arm/boot/dts/sam9x60.dtsi b/arch/arm/boot/dts/sam9x60.dtsi
    > index 326b39328b58..e1d8e3a4cb0b 100644
    > --- a/arch/arm/boot/dts/sam9x60.dtsi
    > +++ b/arch/arm/boot/dts/sam9x60.dtsi
    > @@ -661,6 +661,13 @@
    > status = "disabled";
    > };
    >
    > + rtt: rtt@fffffe20 {
    > + compatible = "microchip,sam9x60-rtt";
    > + reg = <0xfffffe20 0x20>;
    > + interrupts = <1 IRQ_TYPE_LEVEL_HIGH 7>;
    > + clocks = <&clk32k 0>;
    > + };
    > +
    >
    > It doesn't adds the GPBR in sam9x60ek, it adds rtt in sam9x60ek which uses
    > GPBR.
    >
    > >
    > > Just have one patch adding the rtt node to the sam9x60.dtsi and then a
    > > patch adding the RTT to sam9x60ek.
    >
    > Ok, I understand this.
    >
    > > Because the RTT uses the gpbr, it is
    > > a good time to add enable the gpbr, this is a single functionnal change.
    > >
    > > Let's say that for some reason, the RTT patch on sam9x60ek has to be
    > > reverted, then the RTT node is still defined which is good for all the
    > > other eventual users.
    >
    > RTT node would still be defined but GPBR node will not be enabled.
    >
    > If RTT patch contains this change that I understand you want me to merge here:
    >
    > +&gpbr {
    > + status = "okay";
    > +};
    > +
    >
    > then, theoretically, some other IPs using the GPBR (RTC have the
    > possibility of doing this), may be broken by reverting the RTT patch that
    > includes the GPBR enabling patch.
    >

    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.


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

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