linux-kernel - Re: [PATCH v1 1/2] arm: rockchip: Kconfig: remove select ARM_GLOBAL

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Message-ID: <1e268275-0705-8c30-5ea8-799d17278f08@gmail.com>
Date:   Sun, 30 Oct 2022 20:45:12 +0100
From:   Johan Jonker <jbx6244@...il.com>
To:     Heiko Stuebner <heiko@...ech.de>
Cc:     linux@...linux.org.uk, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org
Subject: Re: [PATCH v1 1/2] arm: rockchip: Kconfig: remove select
 ARM_GLOBAL_TIMER



On 10/30/22 20:30, Heiko Stuebner wrote:
> Hi Johan,
> 
> Am Sonntag, 30. Oktober 2022, 19:36:01 CET schrieb Johan Jonker:
>> The clocksource and the sched_clock provided by the arm_global_timer
>> on Rockchip rk3066a/rk3188 are quite unstable because their rates
>> depend on the cpu frequency.
>>
>> Recent changes to the arm_global_timer driver makes it impossible to use.
>>
>> On the other side, the arm_global_timer has a higher rating than the
>> rockchip_timer, it will be selected by default by the time framework
>> while we want to use the stable rockchip clocksource.
>>
>> Let's disable the arm_global_timer in order to have the ROCKCHIP_TIMER
>> (rk3188) or DW_APB_TIMER (rk3066a) selected by default.
> 
> Doing that change won't help you with the issue you see.
> These days kernel images are supposed to run on as many
> platforms as possible with the _same_ kernel image.
> 
> So the muliplatform image build from the kernel's defconfig will
> include most of the time other platforms that will pull in the
> global-timer again.
> 
> 

How about "imply" instead of "select"?
It's no longer useful. One can get rid of if one wants a really lean kernel.

> I do see that you disable the global-timer
> in the rk3066 dtsi in patch2, though this would leave the rk3188
> still using the global-timer. Why not do this in the rk3xxx.dtsi?
> 
> I.e. keep the global-timer node, but add a disabled property
> together with a comment above the status=disabled, describing
> the issue. [This should keep people from re-adding the global-timer
> in the future :-) ]
> 
> Thanks
> Heiko
> 
>> Signed-off-by: Johan Jonker <jbx6244@...il.com>
>> ---
>>
>> ARM: dts: rockchip: disable arm-global-timer for rk3188
>> https://lore.kernel.org/linux-rockchip/1492374441-23336-26-git-send-email-daniel.lezcano@linaro.org/
>>
>> clocksource: arm_global_timer: implement rate compensation whenever source clock changes
>> https://lore.kernel.org/all/20210406130045.15491-2-andrea.merello@gmail.com/
>> ---
>>  arch/arm/mach-rockchip/Kconfig | 2 --
>>  1 file changed, 2 deletions(-)
>>
>> diff --git a/arch/arm/mach-rockchip/Kconfig b/arch/arm/mach-rockchip/Kconfig
>> index b7855cc66..0432a4430 100644
>> --- a/arch/arm/mach-rockchip/Kconfig
>> +++ b/arch/arm/mach-rockchip/Kconfig
>> @@ -15,8 +15,6 @@ config ARCH_ROCKCHIP
>>  	select DW_APB_TIMER_OF
>>  	select REGULATOR if PM
>>  	select ROCKCHIP_TIMER
>> -	select ARM_GLOBAL_TIMER
>> -	select CLKSRC_ARM_GLOBAL_TIMER_SCHED_CLOCK
>>  	select ZONE_DMA if ARM_LPAE
>>  	select PM
>>  	help
>> --
>> 2.20.1
>>
>>
> 
> 
> 
>