[PATCH 2/3] powerpc/mpic: add global timer support

[Scott Wood]

On 03/26/2013 10:23:38 PM, Wang Dongsheng-B40534 wrote:
> 
> 
> > -----Original Message-----
> > From: Wood Scott-B07421
> > Sent: Wednesday, March 27, 2013 1:32 AM
> > To: Wang Dongsheng-B40534
> > Cc: Wood Scott-B07421; Gala Kumar-B11780;  
> linuxppc-dev at lists.ozlabs.org;
> > Li Yang-R58472
> > Subject: Re: [PATCH 2/3] powerpc/mpic: add global timer support
> >
> > On 03/25/2013 10:29:58 PM, Wang Dongsheng-B40534 wrote:
> > >
> > >
> > > > -----Original Message-----
> > > > From: Wood Scott-B07421
> > > > Sent: Saturday, March 23, 2013 6:30 AM
> > > > To: Wang Dongsheng-B40534
> > > > Cc: Wood Scott-B07421; Gala Kumar-B11780;
> > > linuxppc-dev at lists.ozlabs.org;
> > > > Li Yang-R58472
> > > > Subject: Re: [PATCH 2/3] powerpc/mpic: add global timer support
> > > >
> > > > On 03/22/2013 01:14:51 AM, Wang Dongsheng-B40534 wrote:
> > > > >
> > > > >
> > > > > > -----Original Message-----
> > > > > > From: Wood Scott-B07421
> > > > > > Sent: Thursday, March 21, 2013 7:00 AM
> > > > > > To: Wang Dongsheng-B40534
> > > > > > Cc: Wood Scott-B07421; Gala Kumar-B11780;
> > > > > linuxppc-dev at lists.ozlabs.org;
> > > > > > Li Yang-R58472
> > > > > > Subject: Re: [PATCH 2/3] powerpc/mpic: add global timer  
> support
> > > > > >
> > > > > > BTW, the input clock frequency has been similarly scaled,  
> yet
> > > you
> > > > > don't
> > > > > > try to scrounge up that information to get further  
> precision...
> > > > > >
> > > > > Let's go back patch, do you think the code is repeated?
> > > > > I will remove "if (!(priv->flags & FSL_GLOBAL_TIMER))" branch,
> > > there
> > > > > will be no redundant code.
> > > >
> > > > I'd rather that branch be kept and the more complicated branch
> > > deleted,
> > > > and priv->timerfreq frequency be adjusted on initialization to
> > > account
> > > > for the scaler.
> > >
> > > static void convert_ticks_to_time(struct timer_group_priv *priv,
> > >                 const u64 ticks, struct timeval *time) {
> > >         u64 tmp_sec;
> > >
> > >         time->tv_sec = (__kernel_time_t)div_u64(ticks,
> > > priv->timerfreq);
> > >         tmp_sec = (u64)time->tv_sec * (u64)priv->timerfreq;
> > >
> > >         time->tv_usec = (__kernel_suseconds_t)
> > >                 div_u64((ticks - tmp_sec) * 1000000,  
> priv->timerfreq);
> > >
> > >         return;
> > > }
> > >
> > > timer_group_get_freq() {
> > > 	...
> > > 	if (priv->flags & FSL_GLOBAL_TIMER) {
> > > 		div = (1 << (MPIC_TIMER_TCR_CLKDIV_64 >> 8)) * 8;
> > > 		priv->timerfreq /= div;
> > > 	}
> > > 	...
> > > }
> > > Do you want to do that?
> >
> > 	if (priv->flags & FSL_GLOBAL_TIMER)
> > 		priv->timerfreq /= 64;
> >
> > ...but otherwise yes.
> Ok, I would like do this.
> 
> if (priv->flags & FSL_GLOBAL_TIMER) {
> 	div = (1 << (MPIC_TIMER_TCR_CLKDIV_64 >> 8)) * 8;
> 	priv->timerfreq /= div;

Why?  What do you get out of that obfuscation?

-Scott