linux-kernel - Re: [PATCH v5 4/8] ARM: dts: rockchip: disable arm-global-timer for rk3188

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Date:   Mon, 30 Jan 2017 11:21:27 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Alexander Kochetkov <al.kochet@...il.com>
Cc:     Heiko Stuebner <heiko@...ech.de>, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Mark Rutland <mark.rutland@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Caesar Wang <wxt@...k-chips.com>,
        Huang Tao <huangtao@...k-chips.com>
Subject: Re: [PATCH v5 4/8] ARM: dts: rockchip: disable arm-global-timer for
 rk3188

On Tue, Jan 24, 2017 at 03:16:39PM +0300, Alexander Kochetkov wrote:
> clocksource and shed_clock provided by arm-global-timer is quite
> unstable, because their rate depends on cpu frequency.
> So disable arm-global-timer and use clocksource and sched_clock
> from rockchip_timer.
> It is impossible get stable clocksource having rockchip_timer and
> arm-global-timer enabled at the same time. Because arm-global-timer
> looks like a better candidate for the kernel: it has higher
> frequency and rating.
> 
> Disabling arm-global-timer doesn't leave kernel without
> clockevents as there is another clockevent provider (smp-twd).

Hi Alexander,

sorry, I will rewrite the description because of the grammatical errors. I
don't want to give you the feeling I'm lecturing you, my English is not perfect
but it will be simpler to give the full descr with the typos fixed.

"
The clocksource and the sched_clock provided by the arm_global_timer are quite
unstable because their rates depend on the cpu frequency.

On the other side, the arm_global_timer has a higher rating than the
rockchip_timer, it will be selected by default by the time framework while
we want to use the stable rockchip clocksource.

Let's disable the arm_global_timer in order to have the rockchip clocksource
selected by default.
"

This patch should go at the end of the patchset when the clocksource is
implemented in the rockchip_timer.

> Signed-off-by: Alexander Kochetkov <al.kochet@...il.com>
> Reviwed-by: Heiko Stübner <heiko@...ech.de>
> ---
>  arch/arm/boot/dts/rk3188.dtsi |    1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/arm/boot/dts/rk3188.dtsi b/arch/arm/boot/dts/rk3188.dtsi
> index bcf8e03..f677130 100644
> --- a/arch/arm/boot/dts/rk3188.dtsi
> +++ b/arch/arm/boot/dts/rk3188.dtsi
> @@ -546,6 +546,7 @@
>  
>  &global_timer {
>  	interrupts = <GIC_PPI 11 0xf04>;
> +	status = "disabled";
>  };
>  
>  &local_timer {
> -- 
> 1.7.9.5
> 

-- 

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