linux-kernel - RE: [PATCHv3 3/3] clocksource: Add Freescale FlexTimer Module (FTM) timer support

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Date:	Mon, 19 May 2014 02:26:41 +0000
From:	"Li.Xiubo@...escale.com" <Li.Xiubo@...escale.com>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"shawn.guo@...aro.org" <shawn.guo@...aro.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Jingchang Lu <jingchang.lu@...escale.com>
Subject: RE: [PATCHv3 3/3] clocksource: Add Freescale FlexTimer Module (FTM)
 timer support

> > +#define FTM_CNTIN	0x4C
> > +
> > +static void __iomem *clksrc_base;
> > +static void __iomem *clkevt_base;
> > +static unsigned long peroidic_cyc;
> > +static unsigned long ps;
> > +bool big_endian;
> > +
> 
> Usually this is encaspulated in a structure.
> 
> struct ftm_clock_device {
> 	void __iomem *clksrc_base;
> 	...
> };
>
> 
> > +static inline u32 ftm_readl(void __iomem *addr)
> > +{
> > +	if (big_endian)
> 
> I am not a big fan of addressing global variables in the functions, so
> if you can pass the structure pointer around here and the other
> functions instead that would be nice.
> 
> Otherwise the patch sounds ok. Thanks for taking care of encapsulating
> well the functions and commenting the code.
> 

Yes, I did think so.

But some callbacks like ：
+ static u64 ftm_read_sched_clock(void)
+ {
+         return ftm_readl(clksrc_base + FTM_CNT);
+ }

Used by :
+ sched_clock_register(ftm_read_sched_clock,....);

If they are encapsulated in a structure, and should the struct instance
be one global instance too ? I'm doubting whether will this make sense ?


> > +static int __init ftm_calc_closest_round_cyc(unsigned long freq)
> > +{
> > +	ps = 0;
> > +
> > +	do {
> > +		peroidic_cyc = DIV_ROUND_CLOSEST(freq, HZ * (1 << ps++));
> > +	} while (peroidic_cyc > 0xFFFF);
> > +
> > +	if (ps > 7) {
> > +		pr_err("ftm: the max prescaler is %lu > 7\n", ps);
> > +		return -EINVAL;
> > +	}
> > +
> 
> Can you explain how this error can happen ?
> 

Yes, the hardware limitation of the 'ps' is 0~7, and the counter register
Is only using the lower 16 bits.
If the 'freq' value is too big here, then the periodic_cyc may exceed 0xFFFF.

Or should I add some comment here ?


Thanks very much,
BRs
Xiubo