linux-kernel - Re: [PATCH] clocksource: dw_apb_timer

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Date:	Fri, 30 Oct 2015 13:37:01 +0100
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Jisheng Zhang <jszhang@...vell.com>
Cc:	tglx@...utronix.de, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] clocksource: dw_apb_timer_of: support timer-based delay

On 10/30/2015 12:09 PM, Jisheng Zhang wrote:
> Dear Daniel,
>
> On Fri, 30 Oct 2015 11:44:46 +0100
> Daniel Lezcano <daniel.lezcano@....> wrote:
>
>> On 10/30/2015 09:27 AM, Jisheng Zhang wrote:
>>> Implement an ARM delay timer to be used for udelay(). This allows us to
>>> skip the delay loop calibration at boot on Marvell BG2, BG2Q, BG2CD
>>> platforms. And after this patch, udelay() will be unaffected by CPU
>>> frequency changes.
>>>
>>> Signed-off-by: Jisheng Zhang <jszhang@...vell.com>
>>> ---
>>>    drivers/clocksource/Kconfig           | 10 ++++++++++
>>>    drivers/clocksource/dw_apb_timer_of.c | 16 ++++++++++++++++
>>>    2 files changed, 26 insertions(+)
>>>
>>> diff --git a/drivers/clocksource/Kconfig b/drivers/clocksource/Kconfig
>>> index a7726db..7b081805 100644
>>> --- a/drivers/clocksource/Kconfig
>>> +++ b/drivers/clocksource/Kconfig
>>> @@ -29,6 +29,16 @@ config DW_APB_TIMER_OF
>>>    	select DW_APB_TIMER
>>>    	select CLKSRC_OF
>>>
>>> +config DW_APB_TIMER_BASED_DELAY
>>> +	bool "DW APB timer based delay"
>>> +	depends on ARM && DW_APB_TIMER_OF
>>> +	default n
>>> +	help
>>> +	  This option enables support for using the DW APB timer to
>>> +	  implement timer-based delay. It is useful for skiping the
>>> +	  delay loop calibration at boot on some platforms. And the
>>> +	  udelay() will be unaffected by CPU frequency changes.
>>> +
>>
>> Why do you want it to be optional ?
>>
>
> Because in some platforms which has arm arch timer, this dw apb timer
> delay isn't needed, the arch timer is better. So we want it be optional
> so that the platforms which need this feature select it manually when config
> the kernel.

Correct me if I am wrong. If you have the arch timer, you don't need the 
dw apb timer at all, no ? So the selection would be arch arm timer *or* 
dw_apb_timer ? not arch_arm_timer for delay and dw_apb_timer for 
clockevents, right ?


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