[PATCH v5 4/4] powerpc/85xx: add sysfs for pw20 state and altivec idle

[Bhushan Bharat-R65777]

> -----Original Message-----
> From: Wang Dongsheng-B40534
> Sent: Friday, October 18, 2013 8:07 AM
> To: Wood Scott-B07421
> Cc: Bhushan Bharat-R65777; linuxppc-dev at lists.ozlabs.org
> Subject: RE: [PATCH v5 4/4] powerpc/85xx: add sysfs for pw20 state and altivec
> idle
> 
> 
> 
> > -----Original Message-----
> > From: Wood Scott-B07421
> > Sent: Friday, October 18, 2013 12:52 AM
> > To: Wang Dongsheng-B40534
> > Cc: Bhushan Bharat-R65777; Wood Scott-B07421; linuxppc-
> > dev at lists.ozlabs.org
> > Subject: Re: [PATCH v5 4/4] powerpc/85xx: add sysfs for pw20 state and
> > altivec idle
> >
> > On Thu, 2013-10-17 at 00:51 -0500, Wang Dongsheng-B40534 wrote:
> > >
> > > > -----Original Message-----
> > > > From: Bhushan Bharat-R65777
> > > > Sent: Thursday, October 17, 2013 11:20 AM
> > > > To: Wang Dongsheng-B40534; Wood Scott-B07421
> > > > Cc: linuxppc-dev at lists.ozlabs.org
> > > > Subject: RE: [PATCH v5 4/4] powerpc/85xx: add sysfs for pw20 state
> > > > and altivec idle
> > > >
> > > >
> > > >
> > > > > -----Original Message-----
> > > > > From: Wang Dongsheng-B40534
> > > > > Sent: Thursday, October 17, 2013 8:16 AM
> > > > > To: Bhushan Bharat-R65777; Wood Scott-B07421
> > > > > Cc: linuxppc-dev at lists.ozlabs.org
> > > > > Subject: RE: [PATCH v5 4/4] powerpc/85xx: add sysfs for pw20
> > > > > state and altivec idle
> > > > >
> > > > >
> > > > >
> > > > > > -----Original Message-----
> > > > > > From: Bhushan Bharat-R65777
> > > > > > Sent: Thursday, October 17, 2013 1:01 AM
> > > > > > To: Wang Dongsheng-B40534; Wood Scott-B07421
> > > > > > Cc: linuxppc-dev at lists.ozlabs.org
> > > > > > Subject: RE: [PATCH v5 4/4] powerpc/85xx: add sysfs for pw20
> > > > > > state and altivec idle
> > > > > >
> > > > > >
> > > > > >
> > > > > > > -----Original Message-----
> > > > > > > From: Wang Dongsheng-B40534
> > > > > > > Sent: Tuesday, October 15, 2013 2:51 PM
> > > > > > > To: Wood Scott-B07421
> > > > > > > Cc: Bhushan Bharat-R65777; linuxppc-dev at lists.ozlabs.org;
> > > > > > > Wang
> > > > > > Dongsheng-B40534
> > > > > > > Subject: [PATCH v5 4/4] powerpc/85xx: add sysfs for pw20
> > > > > > > state and
> > > > > > altivec idle
> > > > > > >
> > > > > > > +static ssize_t show_pw20_wait_time(struct device *dev,
> > > > > > > +				struct device_attribute *attr, char *buf) {
> > > > > > > +	u32 value;
> > > > > > > +	u64 tb_cycle;
> > > > > > > +	s64 time;
> > > > > > > +
> > > > > > > +	unsigned int cpu = dev->id;
> > > > > > > +
> > > > > > > +	if (!pw20_wt) {
> > > > > > > +		smp_call_function_single(cpu, do_show_pwrmgtcr0, &value,
> > > > 1);
> > > > > > > +		value = (value & PWRMGTCR0_PW20_ENT) >>
> > > > > > > +					PWRMGTCR0_PW20_ENT_SHIFT;
> > > > > > > +
> > > > > > > +		tb_cycle = (1 << (MAX_BIT - value)) * 2;
> > > > > >
> > > > > > Is value = 0 and value = 1 legal? These will make tb_cycle =
> > > > > > 0,
> > > > > >
> > > > > > > +		time = div_u64(tb_cycle * 1000, tb_ticks_per_usec) - 1;
> > > > > >
> > > > > > And time = -1;
> > > > > >
> > > > > Please look at the end of the function, :)
> > > > >
> > > > > "return sprintf(buf, "%llu\n", time > 0 ? time : 0);"
> > > >
> > > > I know you return 0 if value = 0/1, my question was that, is this
> > > > correct as per specification?
> > > >
> > > > Ahh, also for "value" upto 7 you will return 0, no?
> > > >
> > > If value = 0, MAX_BIT - value = 63
> > > tb_cycle = 0xffffffff_ffffffff,
> >
> > Actually, tb_cycle will be undefined because you shifted a 32-bit
> > value
> > (1) by more than 31 bits.  s/1/1ULL/
> >

What Scott is saying is the left shift of "1" for more than 31 will be undefined.
Scott this will be sign-extended, right?

-Bharat

> Actually, we have been discussing this situation that could not have happened.
> See !pw20_wt branch, this branch is read default wait bit.
> The default wait bit is 50, the time is about 1ms.
> The default wait bit cannot less than 50, means the wait entry time cannot
> greater than 1ms.
> We have already begun benchmark test, and we got a preliminary results.
> 55, 56, 57bit looks good, but we need more benchmark to get the default bit.
> 
> 	if (!pw20_wt) {
> 		smp_call_function_single(cpu, do_show_pwrmgtcr0, &value, 1);
> 		value = (value & PWRMGTCR0_PW20_ENT) >>
> 					PWRMGTCR0_PW20_ENT_SHIFT;
> 
> 		tb_cycle = (1 << (MAX_BIT - value)) * 2;
> 		time = div_u64(tb_cycle * 1000, tb_ticks_per_usec) - 1;
> 	} else {
> 		time = pw20_wt;
> 	}
> 
> If it caused confusion, we can add a comment. As I discuss with Bharat.
> 
> > > tb_cycle * 1000 will overflow, but this situation is not possible.
> > > Because if the "value = 0" means this feature will be "disable".
> > > Now The default wait bit is 50(MAX_BIT - value, value = 13), the
> > > PW20/Altivec Idle wait entry time is about 1ms, this time is very
> > > long for wait idle time, and it's cannot be increased(means (MAX_BIT
> > > -
> > > value) cannot greater than 50).
> >
> > Why can it not be increased?
> >
> see above, :)


> 
> -dongsheng
> > -Scott
> >