linux-kernel - RE: [PATCH 5/5] Clocksource: Flextimer: Use Macro for clock source selection.

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Message-ID: <0d12608f04674dcc8138bb23431c8ca4@BY2PR0301MB0613.namprd03.prod.outlook.com>
Date:	Thu, 4 Sep 2014 02:06:46 +0000
From:	"Li.Xiubo@...escale.com" <Li.Xiubo@...escale.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 5/5] Clocksource: Flextimer: Use Macro for clock source
 selection.


> Subject: Re: [PATCH 5/5] Clocksource: Flextimer: Use Macro for clock source
> selection.
> 
> On Tue, 26 Aug 2014, Xiubo Li wrote:
> > FTM source clock is selectable:
> > Source clock can be the system clock, the fixed frequency clock,
> > or an external clock.
> > Fixed frequency clock is an additional clock input to allow the
> > selection of an on chip clock source other than the system clock.
> > Selecting external clock connects FTM clock to a chip level input
> > pin therefore allowing to synchronize the FTM counter with an off
> > chip clock source
> >
> > Clock Source Selection:
> > Selects one of the three FTM counter clock sources.
> >
> > 00 No clock selected. This in effect disables the FTM counter.
> > 01 System clock
> > ---
> > 10 Fixed frequency clock
> > 11 External clock
> >
> > These two will be useful for the alarm on LS1 platform in late future,
> > the system clock's frequency is too high to get a long delay timer when
> > go to sleep, so the fixed or external clock could be used instead.
> 
> And how is that relevant to changing the mask from a hardcoded value
> to a constant? It's still hardcoded at compile time and I don't see
> how that helps chosing the clock at runtime for a particular use case.
> 
> >  #define FTM_SC		0x00
> > +#define FTM_SC_CLKS_NON		0
> > +#define FTM_SC_CLKS_SYS		1
> >  #define FTM_SC_CLK_SHIFT	3
> >  #define FTM_SC_CLK_MASK	(0x3 << FTM_SC_CLK_SHIFT)
> >  #define FTM_SC_CLK(c)	((c) << FTM_SC_CLK_SHIFT)
> > @@ -67,7 +69,7 @@ static inline void ftm_counter_enable(void __iomem *base)
> >  	/* select and enable counter clock source */
> >  	val = ftm_readl(base + FTM_SC);
> >  	val &= ~(FTM_SC_PS_MASK | FTM_SC_CLK_MASK);
> > -	val |= priv->ps | FTM_SC_CLK(1);
> > +	val |= priv->ps | FTM_SC_CLK(FTM_SC_CLKS_SYS);
> >  	ftm_writel(val, base + FTM_SC);
> >  }
> >
> > @@ -77,7 +79,8 @@ static inline void ftm_counter_disable(void __iomem *base)
> >
> >  	/* disable counter clock source */
> >  	val = ftm_readl(base + FTM_SC);
> > -	val &= ~(FTM_SC_PS_MASK | FTM_SC_CLK_MASK);
> > +	val &= ~(FTM_SC_CLK_MASK);
> 
> So you remove the FTM_SC_PS_MASK without mentioning it in the
> changelog. Either this is by mistake or it wants to be documented WHY
> it is not needed in the first place.
> 

This is just prepare for the other new features in the future.

And delay this changes maybe better.

Thanks,

BRs
Xiubo

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