From: Marc Zyngier <maz@kernel.org>
To: Benjamin Gaignard <benjamin.gaignard@st.com>
Cc: <alexandre.torgue@st.com>, <robh+dt@kernel.org>,
<mark.rutland@arm.com>, <devicetree@vger.kernel.org>,
<linux-stm32@st-md-mailman.stormreply.com>,
<linux-arm-kernel@lists.infradead.org>,
<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] ARM: dts: stm32: Enable high resolution timer
Date: Fri, 27 Sep 2019 12:22:13 +0100 [thread overview]
Message-ID: <da48ce9633441cd0186518fa7ce1d528@www.loen.fr> (raw)
In-Reply-To: <20190927084819.645-1-benjamin.gaignard@st.com>
On 2019-09-27 09:48, Benjamin Gaignard wrote:
> Adding always-on makes arm arch_timer claim to be an high resolution
> timer.
> That is possible because power mode won't stop clocking the timer.
The "always-on" is not about the clock. It is about the comparator.
The clock itself is *guaranteed* to always tick. If it didn't, that'd
be
an integration bug, and a pretty bad one.
What you're claiming here is that your CPU never enters a low-power
mode?
Ever? I find this very hard to believe.
Furthermore, claiming that always-on is the way to force the arch-timer
to be an hrtimer is factually wrong. This is what happens *if* this is
the only timer in the system. The only case this is true is for virtual
machines. Anything else has a global timer somewhere that will allow
the arch timers to be used as an hrtimer.
I'm pretty sure you too have a global timer somewhere in your system.
Enable it, and enjoy hrtimers without having to lie about the
properties
of your system! ;-)
M.
>
> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com>
> ---
> arch/arm/boot/dts/stm32mp157c.dtsi | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/arm/boot/dts/stm32mp157c.dtsi
> b/arch/arm/boot/dts/stm32mp157c.dtsi
> index 9b11654a0a39..74f64745d60d 100644
> --- a/arch/arm/boot/dts/stm32mp157c.dtsi
> +++ b/arch/arm/boot/dts/stm32mp157c.dtsi
> @@ -50,6 +50,7 @@
> <GIC_PPI 11 (GIC_CPU_MASK_SIMPLE(4) | IRQ_TYPE_LEVEL_LOW)>,
> <GIC_PPI 10 (GIC_CPU_MASK_SIMPLE(4) | IRQ_TYPE_LEVEL_LOW)>;
> interrupt-parent = <&intc>;
> + always-on;
> };
>
> clocks {
--
Jazz is not dead. It just smells funny...
next prev parent reply other threads:[~2019-09-27 11:22 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-27 8:48 [PATCH] ARM: dts: stm32: Enable high resolution timer Benjamin Gaignard
2019-09-27 11:22 ` Marc Zyngier [this message]
2019-09-27 12:36 ` Benjamin GAIGNARD
2019-09-27 12:41 ` Marc Zyngier
2019-09-27 12:44 ` Benjamin GAIGNARD
2019-09-27 12:59 ` Marc Zyngier
2019-10-14 9:31 ` Benjamin GAIGNARD
2019-10-14 13:48 ` Marc Zyngier
2019-09-27 12:59 ` Sudeep Holla
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