linux-kernel - Re: [PATCH v20 08/17] clocksource/drivers/arm_arch_timer: Rework counter frequency detection.

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Date:   Tue, 31 Jan 2017 11:42:33 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Fu Wei <fu.wei@...aro.org>
Cc:     Linaro ACPI Mailman List <linaro-acpi@...ts.linaro.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>, rruigrok@...eaurora.org,
        Wim Van Sebroeck <wim@...ana.be>, Wei Huang <wei@...hat.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Al Stone <al.stone@...aro.org>,
        Tomasz Nowicki <tn@...ihalf.com>,
        Timur Tabi <timur@...eaurora.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Len Brown <lenb@...nel.org>,
        "Abdulhamid, Harb" <harba@...eaurora.org>,
        Julien Grall <julien.grall@....com>,
        linux-watchdog@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Marc Zyngier <marc.zyngier@....com>,
        Jon Masters <jcm@...hat.com>,
        Christopher Covington <cov@...eaurora.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arm-kernel@...ts.infradead.org,
        G Gregory <graeme.gregory@...aro.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Leo Duran <leo.duran@....com>,
        Hanjun Guo <hanjun.guo@...aro.org>,
        Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Christoffer Dall <christoffer.dall@...aro.org>
Subject: Re: [PATCH v20 08/17] clocksource/drivers/arm_arch_timer: Rework
 counter frequency detection.

On Mon, Jan 30, 2017 at 05:49:59PM +0000, Mark Rutland wrote:
> On Thu, Jan 26, 2017 at 01:49:03PM +0800, Fu Wei wrote:

> > And because Linux kernel is running on Non-secure EL1, so should we
> > skip "SECURE" timer in Linux?
> 
> I guess you mean by checking the GTx Common flags, to see if the timer
> is secure? Yes, we must skip those.
> 
> Looking further at this, the ACPI spec is sorely lacking any statement
> as to the configuration of CNTCTLBase.{CNTSAR,CNTTIDR,CNTACR}, so it's
> not clear if we can access anything in a frame, even if it is listed as
> being a non-secure timer.

Given CNTNSAR.NS<n> enables non-secure access to CNTACR<n>, I guess the
obvious interpretation is that for frames listed as non-secure, this has
been configured to permit non-secure access to the frame and associated
CNTACR<n>.

I will work to that assumption while reviewing, though I still believe
this needs to be clarified in the spec.

Thanks,
Mark.