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

Open Source and information security mailing list archives

Date:	Wed, 16 Dec 2015 15:28:07 +0800
From:	Jisheng Zhang <jszhang@...vell.com>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
CC:	<tglx@...utronix.de>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] clocksource/drivers/pistachio: Fix wrong calculated
 clocksource read value

On Wed, 16 Dec 2015 15:11:25 +0800
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

oops, sorry, should be 0xf0000000. Do I need to send a v2 patch?

> > > 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@...vell.com>    
> > 
> > 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;

should be unsigned int counter = 0xf0000000;

> 	return ~(unsigned long long)counter;
> }
> int main()
> {
> 	printf("%llx\n", pistachio_clocksource_read_cycles());
> 	return 0;
> }
> 
> Thanks,
> Jisheng
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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