linux-kernel - Re: [PATCH v3 4/4] MIPS: CI20: Add second percpu timer for SMP.

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Message-Id: <5C99VQ.EJKI9MPO7XXO1@crapouillou.net>
Date:   Fri, 25 Jun 2021 12:31:17 +0100
From:   Paul Cercueil <paul@...pouillou.net>
To:     周琰杰 <zhouyanjie@...yeetech.com>
Cc:     tsbogend@...ha.franken.de, mturquette@...libre.com,
        sboyd@...nel.org, robh+dt@...nel.org, linux-mips@...r.kernel.org,
        devicetree@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org, dongsheng.qiu@...enic.com,
        aric.pzqi@...enic.com, rick.tyliu@...enic.com,
        sihui.liu@...enic.com, jun.jiang@...enic.com,
        sernia.zhou@...mail.com
Subject: Re: [PATCH v3 4/4] MIPS: CI20: Add second percpu timer for SMP.

Hi Zhou,

Le jeu., juin 24 2021 at 23:06:29 +0800, 周琰杰 (Zhou Yanjie) 
<zhouyanjie@...yeetech.com> a écrit :
> 1.Add a new TCU channel as the percpu timer of core1, this is to
>   prepare for the subsequent SMP support. The newly added channel
>   will not adversely affect the current single-core state.
> 2.Adjust the position of TCU node to make it consistent with the
>   order in jz4780.dtsi file.

That's a bit superfluous, the order matters when adding new nodes, but 
once they are added, moving them around only cause annoyance.

> 
> Signed-off-by: 周琰杰 (Zhou Yanjie) <zhouyanjie@...yeetech.com>
> ---
> 
> Notes:
>     v2:
>     New patch.
> 
>     v2->v3:
>     No change.
> 
>  arch/mips/boot/dts/ingenic/ci20.dts | 21 +++++++++++----------
>  1 file changed, 11 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/mips/boot/dts/ingenic/ci20.dts 
> b/arch/mips/boot/dts/ingenic/ci20.dts
> index 8877c62..70005cc 100644
> --- a/arch/mips/boot/dts/ingenic/ci20.dts
> +++ b/arch/mips/boot/dts/ingenic/ci20.dts
> @@ -118,6 +118,17 @@
>  	assigned-clock-rates = <48000000>;
>  };
> 
> +&tcu {
> +	/*
> +	 * 750 kHz for the system timers and 3 MHz for the clocksources,
> +	 * use channel #0 and #1 for the per cpu system timers, and use
> +	 * channel #2 for the clocksource.
> +	 */
> +	assigned-clocks = <&tcu TCU_CLK_TIMER0>, <&tcu TCU_CLK_TIMER1>,
> +					  <&tcu TCU_CLK_TIMER2>, <&tcu TCU_CLK_OST>;
> +	assigned-clock-rates = <750000>, <750000>, <3000000>, <3000000>;

Ideally you'd set TIMER1 to 3 MHz and TIMER2 to 750 kHz, otherwise it 
kind of breaks support for older kernels (they would still boot, but 
with a very slow clocksource). So in the new DTS you could use the 
timer0 clock for CPU #0, timer1 for the clocksource, and timer2+ for 
cpus > 0.

Cheers,
-Paul

> +};
> +
>  &mmc0 {
>  	status = "okay";
> 
> @@ -522,13 +533,3 @@
>  		bias-disable;
>  	};
>  };
> -
> -&tcu {
> -	/*
> -	 * 750 kHz for the system timer and 3 MHz for the clocksource,
> -	 * use channel #0 for the system timer, #1 for the clocksource.
> -	 */
> -	assigned-clocks = <&tcu TCU_CLK_TIMER0>, <&tcu TCU_CLK_TIMER1>,
> -					  <&tcu TCU_CLK_OST>;
> -	assigned-clock-rates = <750000>, <3000000>, <3000000>;
> -};
> --
> 2.7.4
>