linux-kernel - Re: [PATCH net-next] net: dsa: lan9303: Do not disable switch fabric port 0 at .probe

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Message-ID: <20171024162702.GA12347@lunn.ch>
Date:   Tue, 24 Oct 2017 18:27:02 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Egil Hjelmeland <privat@...l-hjelmeland.no>
Cc:     vivien.didelot@...oirfairelinux.com, f.fainelli@...il.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] net: dsa: lan9303: Do not disable switch fabric
 port 0 at .probe

On Tue, Oct 24, 2017 at 05:14:10PM +0200, Egil Hjelmeland wrote:
> Make the LAN9303 work when lan9303_probe() is called twice.
> 
> For some unknown reason the LAN9303 switch fail to forward data when switch
> fabric port 0 TX is disabled during probe. (Write of LAN9303_MAC_TX_CFG_0
> in lan9303_disable_processing_port().)
> 
> In that situation the switch fabric seem to receive frames, because the ALR
> is learning addresses. But no frames are transmitted on any of the ports.
> 
> In our system lan9303_probe() is called twice, first time
> dsa_register_switch() return -EPROBE_DEFER. As an experiment, modified the
> code to skip writing LAN9303_MAC_TX_CFG_0, port 0 during the first probe.
> Then the switch works as expected.
> 
> Resolve the problem by not calling lan9303_disable_processing_port() on
> port 0 during probe. Ports 1 and 2 are still disabled.
> 
> Although unsatisfying that the exact failure mechanism is not known,
> the patch should not cause any harm.

I agree about this being unsatisfying, but as you said, it fixed your
issue, and it probably does not cause other issues.

Reviewed-by: Andrew Lunn <andrew@...n.ch>

    Andrew