Subject: [PATCH v4] clocksource: arch_timer: Allow the device tree to specify uninitialized timer registers

From: [email-masked] (Daniel Lezcano)
Date: Wed, 26 Nov 2014 13:30:58 +0100

On 11/26/2014 01:06 PM, Heiko St?bner wrote:
> Hi Daniel,
>
> Am Mittwoch, 26. November 2014, 12:51:08 schrieb Daniel Lezcano:
>> Hi Doug, Olof,
>>
>> IIUC, it sounds like this patch is needed from some other patches in
>> arm-soc. Olof was proposing to take this patch through its tree to
>> facilitate the integration.
>>
>> Olof, is it this patch you were worried about ?
>
> I think this is one of two patches in question.
>
> "clocksource: arch_timer: Fix code to use physical timers when requested" [0]
> would be the second one.
>
> And the patch for arm-soc that Olof means would be "ARM: dts: rk3288: add
> arm,cpu-registers-not-fw-configured" [1].

Ok, so IIUC, "clocksource: arch_timer: Fix code to use physical timers 
when requested" should go via arm's tree, right ?

> Heiko
>
> [0]
> https://git.linaro.org/people/daniel.lezcano/linux.git/commit/04f71c2cae54dc26b2a236c787ea8d56c174150b
> [1] https://lkml.org/lkml/2014/11/25/975
>
>>
>> Thanks
>>
>>     -- Daniel
>>
>> On 11/20/2014 12:01 AM, Doug Anderson wrote:
>>> Daniel,
>>>
>>> On Wed, Oct 8, 2014 at 12:33 AM, Sonny Rao <[email-masked]> wrote:
>>>> From: Doug Anderson <[email-masked]>
>>>>
>>>> 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 <[email-masked]>
>>>> Signed-off-by: Sonny Rao <[email-masked]>
>>>> Reviewed-by: Mark Rutland <[email-masked]>
>>>> ---
>>>> 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.
>>>
>>> Thanks!
>

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