[4.4-rc][PATCH] ARM: dts: am4372: fix clock source for arm twd and global timers

[Grygorii Strashko]

On 11/30/2015 03:32 PM, Tero Kristo wrote:
> On 11/30/2015 01:53 PM, Grygorii Strashko wrote:
>> On 11/30/2015 10:25 AM, Tero Kristo wrote:
>>> On 11/27/2015 09:44 PM, Grygorii Strashko wrote:
>>>> ARM TWD and Global timer are clocked by PERIPHCLK which is MPU_CLK/2.
>>>> But now they are clocked by dpll_mpu_m2_ck == MPU_CLK and, as result.
>>>> Timekeeping core misbehaves. For example, execution of command
>>>> "sleep 5" will take 10 sec instead of 5.
>>>>
>>>> Hence, fix it by adding mpu_periphclk ("fixed-factor-clock") and use
>>>> it for clocking ARM TWD and Global timer (same way as on OMAP4).
>>>>
>>>> Cc: Tony Lindgren <tony at atomide.com>
>>>> Cc: Felipe Balbi <balbi at ti.com>
>>>> Cc: Tero Kristo <t-kristo at ti.com>
>>>> Fixes:commit 8cbd4c2f6a99 ("arm: boot: dts: am4372: add ARM timers and
>>>> SCU nodes")
>>>> Signed-off-by: Grygorii Strashko <grygorii.strashko at ti.com>
>>>> ---
>>>>   arch/arm/boot/dts/am4372.dtsi        | 4 ++--
>>>>   arch/arm/boot/dts/am43xx-clocks.dtsi | 8 ++++++++
>>>>   2 files changed, 10 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/arch/arm/boot/dts/am4372.dtsi
>>>> b/arch/arm/boot/dts/am4372.dtsi
>>>> index d83ff9c..de8791a 100644
>>>> --- a/arch/arm/boot/dts/am4372.dtsi
>>>> +++ b/arch/arm/boot/dts/am4372.dtsi
>>>> @@ -74,7 +74,7 @@
>>>>           reg = <0x48240200 0x100>;
>>>>           interrupts = <GIC_PPI 11 IRQ_TYPE_LEVEL_HIGH>;
>>>>           interrupt-parent = <&gic>;
>>>> -        clocks = <&dpll_mpu_m2_ck>;
>>>> +        clocks = <&mpu_periphclk>;
>>>>       };
>>>>
>>>>       local_timer: timer at 48240600 {
>>>> @@ -82,7 +82,7 @@
>>>>           reg = <0x48240600 0x100>;
>>>>           interrupts = <GIC_PPI 13 IRQ_TYPE_LEVEL_HIGH>;
>>>>           interrupt-parent = <&gic>;
>>>> -        clocks = <&dpll_mpu_m2_ck>;
>>>> +        clocks = <&mpu_periphclk>;
>>>>       };
>>>>
>>>>       l2-cache-controller at 48242000 {
>>>> diff --git a/arch/arm/boot/dts/am43xx-clocks.dtsi
>>>> b/arch/arm/boot/dts/am43xx-clocks.dtsi
>>>> index cc88728..2ff58b1 100644
>>>> --- a/arch/arm/boot/dts/am43xx-clocks.dtsi
>>>> +++ b/arch/arm/boot/dts/am43xx-clocks.dtsi
>>>> @@ -259,6 +259,14 @@
>>>>           ti,invert-autoidle-bit;
>>>>       };
>>>>
>>>> +    mpu_periphclk: mpu_periphclk {
>>>> +        #clock-cells = <0>;
>>>> +        compatible = "fixed-factor-clock";
>>>> +        clocks = <&dpll_mpu_ck>;
>>>
>>> I don't think this is correct, ARM core is fed dpll_mpu_m2_ck, where the
>>> divisor value can potentially differ from 1. If you feed this clock
>>> directly from dpll_mpu_ck, you bypass this divisor.
>>
>> Sry. My mistake. I'll update it to use dpll_mpu_m2_ck.
>>
>>>
>>> Did you check what is the impact of cpufreq on the ARM TWD/timers?
>>
>> TWD is cpufreq friendly, ARM GT is not.
> 
> I think the TWD kick period changes with cpufreq also right?

linux/arch/arm/kernel/smp_twd.c has code to handle cpufreq.

> 
> How are the clocks handled with cpufreq? The user just needs to 
> understand that the timers will be screwed if he uses ARM GT? Should we 
> add some sort of dependency to disable the ARM GT if cpufreq is enabled?

Yep. May be, but very good question is how to do that in case of
OMAP multiplatform build which enables most of all config options at once.

There two threads related to this:
[1] http://www.spinics.net/lists/arm-kernel/msg459649.html
[2] http://www.spinics.net/lists/arm-kernel/msg461141.html

Personally, I've do not see better way than [2] right now.


>>>> +        clock-mult = <1>;
>>>> +        clock-div = <2>;
>>>> +    };
>>>> +
>>>>       dpll_ddr_ck: dpll_ddr_ck {
>>>>           #clock-cells = <0>;
>>>>           compatible = "ti,am3-dpll-clock";
>>>>

By the way, does this patch is still correct taking into account dependency
from cpufreq?
Does it make sense update it to use dpll_mpu_ck and resend?

-- 
regards,
-grygorii