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Date:	Thu, 14 Aug 2014 09:02:07 +0000
From:	"fugang.duan@...escale.com" <fugang.duan@...escale.com>
To:	Richard Cochran <richardcochran@...il.com>
CC:	"shawn.guo@...aro.org" <shawn.guo@...aro.org>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH v2 1/1] net: fec: ptp: avoid register access when ipg
 clock is disabled

From: Richard Cochran <richardcochran@...il.com> Sent: Thursday, August 14, 2014 4:43 PM
>To: Duan Fugang-B38611
>Cc: shawn.guo@...aro.org; davem@...emloft.net; netdev@...r.kernel.org
>Subject: Re: [PATCH v2 1/1] net: fec: ptp: avoid register access when ipg
>clock is disabled
>
>On Thu, Aug 14, 2014 at 08:24:39AM +0000, fugang.duan@...escale.com wrote:
>> 1. HW ptp is one feature of FEC IP, when the ethx interface is closed,
>ptp slave cannot sync with master,
>>    So the ptp timer is not accurate, of couse there have discontinuities
>in ptp clock.
>
>No, it just becomes a free running clock.
>
>This is no different than the Linux system clock. It keeps running, even
>if ntpd is not.
>
>> 2. When the ethx net interface is closed, FEC IP clocks are disabled,
>access ptp counter register causes
>>    Hw hang.
>
>Well, then, you need to return an error, don't you?

I know your means. Even if cancel the time_keep work, ptp timer still is running and continutious.
The time_keep work just to avoid timer overrun because FEC just support 32bit counter.

fec_time_keep()
{
...
ns = timecounter_read(&fep->tc);
...
}

static cycle_t fec_ptp_read(const struct cyclecounter *cc)
{
...
        tempval = readl(fep->hwp + FEC_ATIME_CTRL);
        tempval |= FEC_T_CTRL_CAPTURE;
        writel(tempval, fep->hwp + FEC_ATIME_CTRL);

        return readl(fep->hwp + FEC_ATIME);
...
}

And, you said "return an error", I don't know your mean.
In addition, when clock is disabled, FEC ptp counter don't run any more.

>
>> 3. PTP is not separate HW IP, which is one hw feature of FEC IP, when
>the net interface is closed, user
>>    Call clock_gettime() is not reasonable.
>
>Yes, it is. See #1.
>
>Thanks,
>Richard
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