linux-kernel - Re: [PATCH v6 2/2] clocksource: Ingenic: Add support for the Ingenic X1000 OST.

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Message-Id: <512ODQ.64YN0BEY1JJG@crapouillou.net>
Date:   Sat, 18 Jul 2020 15:12:41 +0200
From:   Paul Cercueil <paul@...pouillou.net>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     Zhou Yanjie <zhouyanjie@...yeetech.com>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        robh+dt@...nel.org, tglx@...utronix.de, dongsheng.qiu@...enic.com,
        aric.pzqi@...enic.com, rick.tyliu@...enic.com,
        yanfei.li@...enic.com, sernia.zhou@...mail.com,
        zhenwenjin@...il.com
Subject: Re: [PATCH v6 2/2] clocksource: Ingenic: Add support for the Ingenic
 X1000 OST.

Hi Daniel,

Le ven. 17 juil. 2020 à 10:02, Daniel Lezcano 
<daniel.lezcano@...aro.org> a écrit :
> On 17/07/2020 08:13, Zhou Yanjie wrote:
>>  Hi Daniel,
>> 
>>  在 2020/7/17 下午12:20, Daniel Lezcano 写道:
>>>  On 10/07/2020 19:02, 周琰杰 (Zhou Yanjie) wrote:
>>>>  X1000 and SoCs after X1000 (such as X1500 and X1830) had a 
>>>> separate
>>>>  OST, it no longer belongs to TCU. This driver will register both a
>>>>  clocksource and a sched_clock to the system.
>>>> 
>>>>  Tested-by: 周正 (Zhou Zheng) <sernia.zhou@...mail.com>
>>>>  Co-developed-by: 漆鹏振 (Qi Pengzhen) <aric.pzqi@...enic.com>
>>>>  Signed-off-by: 漆鹏振 (Qi Pengzhen) <aric.pzqi@...enic.com>
>>>>  Signed-off-by: 周琰杰 (Zhou Yanjie) <zhouyanjie@...yeetech.com>
>>>>  Reviewed-by: Paul Cercueil <paul@...pouillou.net>
>>>>  ---
>>>> 
>>>>  Notes:
>>>>       v1->v2:
>>>>       Fix compile warnings.
>>>>       Reported-by: kernel test robot <lkp@...el.com>
>>>>            v2->v3:
>>>>       No change.
>>>>            v3->v4:
>>>>       1.Rename "ost" to "sysost"
>>>>       1.Remove unrelated changes.
>>>>       2.Remove ost_clock_parent enum.
>>>>       3.Remove ost->percpu_timer_channel/ost->global_timer_channel.
>>>>       4.Set up independent .recalc_rate/.set_rate for percpu/global
>>>>  timer.
>>>>       5.No longer call functions in variable declarations.
>>>>            v4->v5:
>>>>       Use "of_io_request_and_map()" instead "of_iomap()".
>>>>       Suggested-by: Paul Cercueil <paul@...pouillou.net>
>>>>            v5->v6:
>>>>       No change.
>>>> 
>>>>    drivers/clocksource/Kconfig          |  11 +
>>>>    drivers/clocksource/Makefile         |   1 +
>>>>    drivers/clocksource/ingenic-sysost.c | 539
>>>>  +++++++++++++++++++++++++++++++++++
>>>>    3 files changed, 551 insertions(+)
>>>>    create mode 100644 drivers/clocksource/ingenic-sysost.c
>>>> 
>>>>  diff --git a/drivers/clocksource/Kconfig 
>>>> b/drivers/clocksource/Kconfig
>>>>  index 91418381fcd4..1bca8b8fb30f 100644
>>>>  --- a/drivers/clocksource/Kconfig
>>>>  +++ b/drivers/clocksource/Kconfig
>>>>  @@ -696,6 +696,17 @@ config INGENIC_TIMER
>>>>        help
>>>>          Support for the timer/counter unit of the Ingenic JZ SoCs.
>>>>    +config INGENIC_SYSOST
>>>>  +    bool "Clocksource/timer using the SYSOST in Ingenic X SoCs"
>>>  We usually use silent options and let the platform's Kconfig 
>>> enable it.
>>>  We show up the option only when COMPILE_TEST is enabled.
>>> 
>>>  Is there a reason to do it differently?
>> 
>> 
>>  Do you mean
>> 
>>  bool "Clocksource/timer using the SYSOST in Ingenic X SoCs"
>> 
>>  or
>> 
>>  default MACH_INGENIC ?
> 
> Both, no default here.
> 
> eg.
> 
> bool "Clocksource/timer using the SYSOST in Ingenic X SoCs" if 
> COMPILE_TEST
> 
> and
> 
> in arch/mips/Kconfig in the config MACH_INGENIC section :
> 
> ...
> select INGENIC_SYSOST
> ...

Disagreed. That's not how we do things on MIPS. Selecting MACH_INGENIC 
means "this kernel will support Ingenic SoCs", but not that it will 
only support these. Hence the depends on MIPS / default MACH_INGENIC.

As for the select INGENIC_SYSOST, this driver only applies to a few 
SoCs, I certainly don't want it to be force-enabled. I don't even wait 
it to be force-enabled on X1000, since it is optional there too.

Cheers,
-Paul

> 
>>  This driver has some origins from "INGENIC_TIMER" driver and
>>  "INGENIC_OST" driver.
>>  Early Ingenic processors used TCU (timer/counter unit, has 6 or 8
>>  generic timer channels) to provide clocksource and clockevent (both 
>> with
>>  only 16bit precision). This part of the processor can only use
>>  "INGENIC_TIMER" driver.
>> 
>>  Later processors provide an independent 32bit or 64bit timer channel
>>  (still under TCU, known as ost channel, this channel can not 
>> generate
>>  interrupt) to provid higher precision clocksource. The "INGENIC_OST"
>>  driver is for this channel. These processors can use "INGENIC_TIMER"
>>  driver, but using "INGENIC_OST" driver to provide higher precision
>>  clocksource would be a better choice (clockevent still needs to be
>>  provided by generic timer channel of TCU, and still 16bit 
>> precision).
>> 
>>  And the recent processors provide a SYSOST components, it is 
>> independent
>>  from TCU, including a 64bit timer channel for clocksource and a 
>> 32bit
>>  timer channel for clockevent. Although these processors can also use
>>  "INGENIC_TIMER" driver, but the better choice is completely 
>> independent
>>  use of "INGENIC_SYSOST" driver to provide higher precision 
>> clocksource
>>  and clockevent.
> 
> Ok, the rating should do the job then.
> 
> Thanks for the explanation.
> 
>>  You may have already noticed that this independent SYSOST component 
>> is
>>  like an upgraded and streamlined TCU, which only retains one generic
>>  timer channel that can generate interrupts, upgrade it from 16bit to
>>  32bit, and then retain the 64bit ost channel. so the driver code and
>>  Kconfig code of this patch is largely referenced
>>  "INGENIC_TIMER" driver and "INGENIC_OST" driver.
>> 
>>  Thanks and best regards!
>> 
>>>>  +    default MACH_INGENIC
>>>>  +    depends on MIPS || COMPILE_TEST
>>>>  +    depends on COMMON_CLK
>>>>  +    select MFD_SYSCON
>>>>  +    select TIMER_OF
>>>>  +    select IRQ_DOMAIN
>>>>  +    help
>>>>  +      Support for the SYSOST of the Ingenic X Series SoCs.
>>>>  +
>>>  [ ... ]
>>> 
>>> 
> 
> 
> --
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