linux-kernel - Re: [PATCH 15/17] arm64: allwinner: dts: add DTSI file for R329 SoC

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Date:   Wed, 18 Aug 2021 21:32:53 -0500
From:   Samuel Holland <samuel@...lland.org>
To:     Icenowy Zheng <icenowy@...eed.com>,
        Maxime Ripard <maxime@...no.tech>
Cc:     Rob Herring <robh+dt@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Andre Przywara <andre.przywara@....com>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-sunxi@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 15/17] arm64: allwinner: dts: add DTSI file for R329 SoC

On 8/18/21 4:15 AM, Icenowy Zheng wrote:
> 于 2021年8月18日 GMT+08:00 下午5:01:39, Maxime Ripard <maxime@...no.tech> 写到:
>> On Mon, Aug 02, 2021 at 02:22:10PM +0800, Icenowy Zheng wrote:
>>> +		ccu: clock@...1000 {
>>> +			compatible = "allwinner,sun50i-r329-ccu";
>>> +			reg = <0x02001000 0x1000>;
>>> +			clocks = <&osc24M>, <&rtc 0>, <&rtc 2>;
>>> +			clock-names = "hosc", "losc", "iosc";
>>
>> Do we have a clock tree for the RTC? Is it the same than the H616?
> 
> Nope, it's the same with H6 because of external LOSC crystal is
> possible. (Although production M2A SoMs has it NC for cost control.)

It is not the same as the H6, either. The clock tree _is_ identical to the D1,
which has three diagrams on pages 363-364 of its user manual here:

https://dl.linux-sunxi.org/D1/D1_User_Manual_V0.1_Draft_Version.pdf

Compared to the H6, the R329/D1:
 - Loses the LOSC calibration circuit
 - Gains a third mux input for LOSC (not external 32k) to fanout
 - Gains a mux to choose between LOSC and HOSC/750 for the RTC clock
 - Gains an SPI bus clock input divided from the PRCM AHB

Compared to the H616, the R329/D1:
 - Has an external 32k crystal input
   - Gains the IOSC vs. external 32k crystal mux for LOSC
   - Switches fanout mux input #1 from pll_periph0/N to external 32k
 - Gains a mux to choose between LOSC and HOSC/750 for the RTC clock
 - Gains an SPI bus clock input divided from the PRCM AHB

So the R329/D1 RTC has three inputs:
 - SPI clock from PRCM
 - 24 MHz DCXO crystal
 - 32 kHz external crystal (optional)

and four outputs:
 - 16 MHz "IOSC" RC oscillator
 - 32 kHz "LOSC"
 - ~1 kHz for RTC timekeeping
 - 32 kHz fanout

(Arguably, since the 24 MHz DCXO can be turned on/off from the RTC registers, it
should be an "output" and not an "input".)

Regards,
Samuel