linux-kernel - Re: [PATCH v4] clocksource: arch_timer: Allow the device tree to specify uninitialized timer registers

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Message-ID: <54725472.7010804@linaro.org>
Date:	Sun, 23 Nov 2014 22:41:06 +0100
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Doug Anderson <dianders@...omium.org>
CC:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Olof Johansson <olof@...om.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Sudeep Holla <Sudeep.Holla@....com>,
	Mark Rutland <Mark.Rutland@....com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Marc Zyngier <marc.zyngier@....com>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Nathan Lynch <Nathan_Lynch@...tor.com>,
	Rob Herring <robh+dt@...nel.org>,
	Sonny Rao <sonnyrao@...omium.org>,
	Heiko Stübner <heiko@...ech.de>
Subject: Re: [PATCH v4] clocksource: arch_timer: Allow the device tree to
 specify uninitialized timer registers

On 11/20/2014 12:01 AM, Doug Anderson wrote:
> Daniel,
>
> On Wed, Oct 8, 2014 at 12:33 AM, Sonny Rao <sonnyrao@...omium.org> wrote:
>> From: Doug Anderson <dianders@...omium.org>
>>
>> Some 32-bit (ARMv7) systems are architected like this:
>>
>> * The firmware doesn't know and doesn't care about hypervisor mode and
>>    we don't want to add the complexity of hypervisor there.
>>
>> * The firmware isn't involved in SMP bringup or resume.
>>
>> * The ARCH timer come up with an uninitialized offset (CNTVOFF)
>>    between the virtual and physical counters.  Each core gets a
>>    different random offset.
>>
>> * The device boots in "Secure SVC" mode.
>>
>> * Nothing has touched the reset value of CNTHCTL.PL1PCEN or
>>    CNTHCTL.PL1PCTEN (both default to 1 at reset)
>>
>> On systems like the above, it doesn't make sense to use the virtual
>> counter.  There's nobody managing the offset and each time a core goes
>> down and comes back up it will get reinitialized to some other random
>> value.
>>
>> This adds an optional property which can inform the kernel of this
>> situation, and firmware is free to remove the property if it is going
>> to initialize the CNTVOFF registers when each CPU comes out of reset.
>>
>> Currently, the best course of action in this case is to use the
>> physical timer, which is why it is important that CNTHCTL hasn't been
>> changed from its reset value and it's a reasonable assumption given
>> that the firmware has never entered HYP mode.
>>
>> Note that it's been said that on ARMv8 systems the firmware and
>> kernel really can't be architected as described above.  That means
>> using the physical timer like this really only makes sense for ARMv7
>> systems.
>>
>> Signed-off-by: Doug Anderson <dianders@...omium.org>
>> Signed-off-by: Sonny Rao <sonnyrao@...omium.org>
>> Reviewed-by: Mark Rutland <mark.rutland@....com>
>> ---
>> Changes in v2:
>> - Add "#ifdef CONFIG_ARM" as per Will Deacon
>>
>> Changes in v3:
>> - change property name to arm,cntvoff-not-fw-configured and specify
>>    that the value of CNTHCTL.PL1PC(T)EN must still be the reset value
>>    of 1 as per Mark Rutland
>>
>> Changes in v4:
>> - change property name to arm,cpu-registers-not-fw-configured and
>>    specify that all cpu registers must have architected reset values
>>    per Mark Rutland
>> - change from "#ifdef CONFIG_ARM" to "if (IS_ENABLED(CONFIG_ARM))" per
>>    Arnd Bergmann
>> ---
>>   Documentation/devicetree/bindings/arm/arch_timer.txt | 8 ++++++++
>>   drivers/clocksource/arm_arch_timer.c                 | 8 ++++++++
>>   2 files changed, 16 insertions(+)
>
> Do you know what the status of this patch is?  This patch and Sonny's
> patch at <https://patchwork.kernel.org/patch/5051901/> are needed on
> Rockchip rk3288 for some specific things:
>
> 1. To make SMP happy with coreboot.
>
> 2. To (I assume) make SMP happy after S2R (no matter which firmware is
> used since I don't think anyone has PSCI for rk3288).
>
> ...we still need a DTS entry atop these patches, but that's trivial to
> add once these land.

Hi Doug,

sounds like I forgot it. Thanks for the heads up.

Applied for 3.19.

   -- Daniel


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