Subject: [4.4-rc][PATCH] ARM: dts: am4372: fix clock source for arm twd and global timers

From: [email-masked] (Tero Kristo)
Date: Mon, 30 Nov 2015 10:25:56 +0200

On 11/27/2015 09:44 PM, Grygorii Strashko wrote:
> ARM TWD and Global timer are clocked by PERIPHCLK which is MPU_CLK/2.
> But now they are clocked by dpll_mpu_m2_ck == MPU_CLK and, as result.
> Timekeeping core misbehaves. For example, execution of command
> "sleep 5" will take 10 sec instead of 5.
>
> Hence, fix it by adding mpu_periphclk ("fixed-factor-clock") and use
> it for clocking ARM TWD and Global timer (same way as on OMAP4).
>
> Cc: Tony Lindgren <[email-masked]>
> Cc: Felipe Balbi <[email-masked]>
> Cc: Tero Kristo <[email-masked]>
> Fixes:commit 8cbd4c2f6a99 ("arm: boot: dts: am4372: add ARM timers and SCU nodes")
> Signed-off-by: Grygorii Strashko <[email-masked]>
> ---
>   arch/arm/boot/dts/am4372.dtsi        | 4 ++--
>   arch/arm/boot/dts/am43xx-clocks.dtsi | 8 ++++++++
>   2 files changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm/boot/dts/am4372.dtsi b/arch/arm/boot/dts/am4372.dtsi
> index d83ff9c..de8791a 100644
> --- a/arch/arm/boot/dts/am4372.dtsi
> +++ b/arch/arm/boot/dts/am4372.dtsi
> @@ -74,7 +74,7 @@
>   		reg = <0x48240200 0x100>;
>   		interrupts = <GIC_PPI 11 IRQ_TYPE_LEVEL_HIGH>;
>   		interrupt-parent = <&gic>;
> -		clocks = <&dpll_mpu_m2_ck>;
> +		clocks = <&mpu_periphclk>;
>   	};
>
>   	local_timer: timer at 48240600 {
> @@ -82,7 +82,7 @@
>   		reg = <0x48240600 0x100>;
>   		interrupts = <GIC_PPI 13 IRQ_TYPE_LEVEL_HIGH>;
>   		interrupt-parent = <&gic>;
> -		clocks = <&dpll_mpu_m2_ck>;
> +		clocks = <&mpu_periphclk>;
>   	};
>
>   	l2-cache-controller at 48242000 {
> diff --git a/arch/arm/boot/dts/am43xx-clocks.dtsi b/arch/arm/boot/dts/am43xx-clocks.dtsi
> index cc88728..2ff58b1 100644
> --- a/arch/arm/boot/dts/am43xx-clocks.dtsi
> +++ b/arch/arm/boot/dts/am43xx-clocks.dtsi
> @@ -259,6 +259,14 @@
>   		ti,invert-autoidle-bit;
>   	};
>
> +	mpu_periphclk: mpu_periphclk {
> +		#clock-cells = <0>;
> +		compatible = "fixed-factor-clock";
> +		clocks = <&dpll_mpu_ck>;

I don't think this is correct, ARM core is fed dpll_mpu_m2_ck, where the 
divisor value can potentially differ from 1. If you feed this clock 
directly from dpll_mpu_ck, you bypass this divisor.

Did you check what is the impact of cpufreq on the ARM TWD/timers?

-Tero

> +		clock-mult = <1>;
> +		clock-div = <2>;
> +	};
> +
>   	dpll_ddr_ck: dpll_ddr_ck {
>   		#clock-cells = <0>;
>   		compatible = "ti,am3-dpll-clock";
>