Re: [PATCH] clocksource/drivers/pistachio: Fix wrong calculated clocksource read value

[Daniel Lezcano]

On 12/16/2015 08:11 AM, Jisheng Zhang wrote:
> Dear Daniel,
>
> On Tue, 15 Dec 2015 21:59:30 +0100 Daniel Lezcano wrote:
>
> > On 11/25/2015 04:42 PM, Jisheng Zhang wrote:
> > > Let's assume the counter value is 0xf000000, the pistachio clocksource
> > > read cycles function would return 0xffffffff0fffffff, but it should
> > > return 0xfffffff.
> > >
> > > We fix this issue by calculating bitwise-not counter, then cast to
> > > cycle_t.
> > >
> > > Signed-off-by: Jisheng Zhang <jszhang@xxxxxxxxxxx>
> >
> > Hi Jisheng,
> >
> > I tried to reproduce this behavior on x86_64 but without success.
> >
> > On which architecture did you produce this result ? Do you have a simple
> > test program to check with ?
>
> I have no HW platforms with pistachio, just read the code and run the
> following test code in x86_64 and x86_32:
>
> #include <stdio.h>
> unsigned long long pistachio_clocksource_read_cycles()
> {
> 	unsigned int counter = 0xf000000;
> 	return ~(unsigned long long)counter;
> }
> int main()
> {
> 	printf("%llx\n", pistachio_clocksource_read_cycles());
> 	return 0;
> }

Ok, I reproduced it. I had an issue with the signed/unsigned type.

That's a good catch !


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