Re: [PATCH] clocksource: dw_apb_timer_of: support timer-based delay

[Daniel Lezcano]

On 11/02/2015 03:51 AM, Jisheng Zhang wrote:
> 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@xxxxxxxxxxx>
> > > > > ---
> > > > >     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?

If I follow the logic of arch_arm_timer is better than dw_apb timer.

1. The arch_arm_timer is present

 => dw_apb timer is not used at all

 CONFIG_ARM_ARCH_TIMER=y
 # CONFIG_DW_APB_TIMER is not set

2. The arch_arm_timer is *not* present

 => dw_apb_timer is used with delay code

 # CONFIG_ARM_ARCH_TIMER is not set
 CONFIG_DW_APB_TIMER=y

In both cases, DW_APB_TIMER_BASED_DELAY is not needed.


--
 <http://www.linaro.org/> Linaro.org â Open source software for ARM SoCs

Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/