netdev - Re: [PATCH v7 06/11] net: pch_gbe: Only enable MAC when PHY link is active

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Date:   Wed, 27 Jun 2018 19:30:14 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Paul Burton <paul.burton@...s.com>
Cc:     netdev@...r.kernel.org, "David S . Miller" <davem@...emloft.net>
Subject: Re: [PATCH v7 06/11] net: pch_gbe: Only enable MAC when PHY link is
 active

On Tue, Jun 26, 2018 at 05:06:07PM -0700, Paul Burton wrote:
> When using a PHY connected via RGMII, as the pch_gbe driver presumes is
> the case, the RX clock is provided by the PHY to the MAC. Various PHYs,
> including both the AR8031 used by the Minnowboard & the RTL8211E used by
> the MIPS Boston development board, will stop generating the RX clock
> when the ethernet link is down (eg. the ethernet cable is unplugged).
> 
> Various pieces of functionality in the EG20T MAC, ranging from basics
> like completing a MAC reset to programming MAC addresses, rely upon the
> RX clock being provided. When the clock is not provided these pieces of
> functionality simply never complete, and the busy bits that indicate
> they're in progress remain set indefinitely.
> 
> The pch_gbe driver currently requires that the RX clock is always
> provided, and attempts to enforce this by disabling the hibernation
> feature of the AR8031 PHY to keep it generating the RX clock. This patch
> moves us away from this model by only configuring the MAC when the PHY
> indicates that the ethernet link is up. When the link is up we should be
> able to safely expect that the RX clock is being provided, and therefore
> safely reset & configure the MAC.

Hi Paul

I like the concept, but the implementation is not clear. Maybe it just
needs more details in the commit message. What has the watchdog got to
do with link up?

And what happens on link down? Does the MAC need shutting down? I
don't see such code here.

    Andrew