linux-kernel - Re: [PATCH 4/4] MIPS: CI20: Reduce MSC0 frequency and add second percpu timer for SMP.

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Date:   Tue, 22 Jun 2021 13:39:02 +0100
From:   Paul Cercueil <paul@...pouillou.net>
To:     周琰杰 <zhouyanjie@...yeetech.com>
Cc:     tsbogend@...ha.franken.de, robh+dt@...nel.org,
        linux-mips@...r.kernel.org, devicetree@...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 4/4] MIPS: CI20: Reduce MSC0 frequency and add second
 percpu timer for SMP.

Hi Zhou,

Le mar., juin 22 2021 at 15:37:25 +0800, 周琰杰 (Zhou Yanjie) 
<zhouyanjie@...yeetech.com> a écrit :
> 1.On the hardware of CI20 v1, when the MSC0 clock is 50MHz, there is
>   a certain probability that the communication with the SD card will
>   be abnormal, and the file system will be damaged in severe cases.
>   Limiting the maximum MSC0 clock frequency to 25MHz can solve this
>   problem.

That doesn't prevent anything, since you could very well use a recent 
kernel with an older device tree.

Besides, the PM does say that 50 MHz bus clock is supported, so I 
suspect that your problem is actually a driver issue.

The proper way to work around it, temporarily or not, would be to set 
the max frequency to 25 MHz in the driver itself, if the board's 
compatible strings matches ingenic,ci20.

Cheers,
-Paul

> 2.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.
> 3.Adjust the position of TCU node to make it consistent with the
>   order in jz4780.dtsi file.
> 
> Signed-off-by: 周琰杰 (Zhou Yanjie) <zhouyanjie@...yeetech.com>
> ---
>  arch/mips/boot/dts/ingenic/ci20.dts | 23 ++++++++++++-----------
>  1 file changed, 12 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/mips/boot/dts/ingenic/ci20.dts 
> b/arch/mips/boot/dts/ingenic/ci20.dts
> index 8877c62..58123e0 100644
> --- a/arch/mips/boot/dts/ingenic/ci20.dts
> +++ b/arch/mips/boot/dts/ingenic/ci20.dts
> @@ -118,11 +118,22 @@
>  	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>;
> +};
> +
>  &mmc0 {
>  	status = "okay";
> 
>  	bus-width = <4>;
> -	max-frequency = <50000000>;
> +	max-frequency = <25000000>;
> 
>  	pinctrl-names = "default";
>  	pinctrl-0 = <&pins_mmc0>;
> @@ -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
>