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

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Message-ID: <20151102105113.72aade85@xhacker>
Date:	Mon, 2 Nov 2015 10:51:13 +0800
From:	Jisheng Zhang <jszhang@...vell.com>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
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

Dear Daniel,

On Fri, 30 Oct 2015 13:37:01 +0100
Daniel Lezcano wrote:

> 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 

Yes, I don't need the dw apb timer if we have arch timer,

> 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 ?

Yes, if we have arch timer, I prefer to use it for clockevent and delay.

Could you please provide suggestion how to handle this case?

Thanks,
Jisheng

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