Date: Wed, 16 Dec 2015 15:11:25 +0800
From: Jisheng Zhang <jszhang@marvell.com>
To: Daniel Lezcano <daniel.lezcano@linaro.org>
CC: <tglx@linutronix.de>, <linux-kernel@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] clocksource/drivers/pistachio: Fix wrong calculated
 clocksource read value
Message-ID: <20151216151125.1e91b4f4@xhacker>
In-Reply-To: <56707F32.3030405@linaro.org>
References: <1448466169-5230-1-git-send-email-jszhang@marvell.com>
	<56707F32.3030405@linaro.org>
MIME-Version: 1.0
Content-Type: text/plain; charset="US-ASCII"
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1244
Lines: 43

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@marvell.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;
	return ~(unsigned long long)counter;
}
int main()
{
	printf("%llx\n", pistachio_clocksource_read_cycles());
	return 0;
}

Thanks,
Jisheng
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/