netdev - Re: [PATCH v2 1/1] net: fec: ptp: fix convergence issue to support LinuxPTP stack

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Date:	Wed, 15 Oct 2014 16:40:39 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	b38611@...escale.com
Cc:	richardcochran@...il.com, netdev@...r.kernel.org,
	bhutchings@...arflare.com, b20596@...escale.com
Subject: Re: [PATCH v2 1/1] net: fec: ptp: fix convergence issue to support
 LinuxPTP stack

From: Fugang Duan <b38611@...escale.com>
Date: Wed, 15 Oct 2014 17:30:12 +0800

> iMX6SX IEEE 1588 module has one hw issue in capturing the ATVR register.
> The current SW flow is:
> 		ENET0->ATCR |= ENET_ATCR_CAPTURE_MASK;
> 		ts_counter_ns = ENET0->ATVR;
> The ATVR value is not expected value that cause LinuxPTP stack cannot be convergent.
> 
> ENET Block Guide/ Chapter for the iMX6SX (PELE) address the issue:
> After set ENET_ATCR[Capture], there need some time cycles before the counter
> value is capture in the register clock domain. The wait-time-cycles is at least
> 6 clock cycles of the slower clock between the register clock and the 1588 clock.
> So need something like:
> 		ENET0->ATCR |= ENET_ATCR_CAPTURE_MASK;
> 		wait();
> 		ts_counter_ns = ENET0->ATVR;
> 
> For iMX6SX, the 1588 ts_clk is fixed to 25Mhz, register clock is 66Mhz, so the
> wait-time-cycles must be greater than 240ns (40ns * 6). The patch add 1us delay
> before cpu read ATVR register.
> 
> Changes V2:
> Modify the commit/comments log to describe the issue clearly.
> 
> Signed-off-by: Fugang Duan <B38611@...escale.com>

Applied, thanks.
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