From: Marc Zyngier <maz@kernel.org>
To: Benjamin GAIGNARD <benjamin.gaignard@st.com>
Cc: mark.rutland@arm.com, devicetree@vger.kernel.org,
Alexandre TORGUE <alexandre.torgue@st.com>,
linux-kernel@vger.kernel.org, robh+dt@kernel.org,
linux-stm32@st-md-mailman.stormreply.com,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] ARM: dts: stm32: Enable high resolution timer
Date: Fri, 27 Sep 2019 13:41:03 +0100 [thread overview]
Message-ID: <ff11797da8f049b354797689754fde52@www.loen.fr> (raw)
In-Reply-To: <341949c8-7864-5d65-2797-988022724a4c@st.com>
On 2019-09-27 13:36, Benjamin GAIGNARD wrote:
> On 9/27/19 1:22 PM, Marc Zyngier wrote:
>> 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! ;-)
>
> Hi Marc,
>
> This SoC doesn't have any other global timer. Use arch_time is the
> only
> we have to provide hrtimer on this system.
And you don't have any form of power management either? What happens
when
your CPU goes into idle? If your system does any form of power
management
*and* doesn't have a separate timer, it is remarkably broken.
M.
--
Jazz is not dead. It just smells funny...
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2019-09-27 12:41 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
2019-09-27 12:36 ` Benjamin GAIGNARD
2019-09-27 12:41 ` Marc Zyngier [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=ff11797da8f049b354797689754fde52@www.loen.fr \
--to=maz@kernel.org \
--cc=alexandre.torgue@st.com \
--cc=benjamin.gaignard@st.com \
--cc=devicetree@vger.kernel.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-stm32@st-md-mailman.stormreply.com \
--cc=mark.rutland@arm.com \
--cc=robh+dt@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).