netdev - Re: [PATCH v2 1/1] net: fec: ptp: avoid register access when ipg clock is disabled

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Message-ID: <20140814084251.GC7555@netboy>
Date:	Thu, 14 Aug 2014 10:42:51 +0200
From:	Richard Cochran <richardcochran@...il.com>
To:	"fugang.duan@...escale.com" <fugang.duan@...escale.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

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?

> 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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