netdev - Re: [PATCH v6 net-next 6/7] net: ethernet: ti: am65-cpsw-qos: Add Frame Preemption MAC Merge support

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Date: Thu, 30 Nov 2023 15:22:22 +0200
From: Vladimir Oltean <vladimir.oltean@....com>
To: Roger Quadros <rogerq@...nel.org>
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
	pabeni@...hat.com, s-vadapalli@...com, r-gunasekaran@...com,
	vigneshr@...com, srk@...com, horms@...nel.org, p-varis@...com,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 net-next 6/7] net: ethernet: ti: am65-cpsw-qos: Add
 Frame Preemption MAC Merge support

On Thu, Nov 30, 2023 at 01:49:03PM +0200, Roger Quadros wrote:
> Thanks for the debug instructions. Indeed lldpad tries to enable MM TX and the
> network drivers set_mm() hook gets called and returns success but still
> lldpad sees some error.
> 
> I've also confirmed that ethnl_set_mm() runs successfully and returns 1.
> I suppose something is going wrong in user-space with libnl?
> 
> Nov 21 11:50:02 am62xx lldpad[708]: eth0: Link partner preemption capability supported
> Nov 21 11:50:02 am62xx lldpad[708]: eth0: Link partner preemption capability not enabled
> Nov 21 11:50:02 am62xx lldpad[708]: eth0: Link partner preemption capability not active
> Nov 21 11:50:02 am62xx lldpad[708]: eth0: Link partner minimum fragment size: 124 octets
> Nov 21 11:50:02 am62xx lldpad[708]: eth0: initiating MM verification with a retry interval of 134 ms...
> Nov 21 11:50:02 am62xx lldpad[708]: ethtool: kernel reports: integer out of range
> 
> 
> full debug log is below.

Ah, you got confused. Openlldp issues multiple ETHTOOL_MSG_MM_SET
netlink messages. What you observe is that one of them succeeds, and
then another one returns -ERANGE before even calling the driver's
set_mm() method.

And that comes from here in net/ethtool/mm.c:

149 const struct nla_policy ethnl_mm_set_policy[ETHTOOL_A_MM_MAX + 1] = {
150 »       [ETHTOOL_A_MM_HEADER]»  »       = NLA_POLICY_NESTED(ethnl_header_policy),
151 »       [ETHTOOL_A_MM_VERIFY_ENABLED]»  = NLA_POLICY_MAX(NLA_U8, 1),
152 »       [ETHTOOL_A_MM_VERIFY_TIME]»     = NLA_POLICY_RANGE(NLA_U32, 1, 128), // <---- here
153 »       [ETHTOOL_A_MM_TX_ENABLED]»      = NLA_POLICY_MAX(NLA_U8, 1),
154 »       [ETHTOOL_A_MM_PMAC_ENABLED]»    = NLA_POLICY_MAX(NLA_U8, 1),
155 »       [ETHTOOL_A_MM_TX_MIN_FRAG_SIZE]»= NLA_POLICY_RANGE(NLA_U32, 60, 252),
156 };

You are reporting in .get_mm() a maximum verify time which is larger
than the core ethtool is willing to accept in a further .set_mm() call.
And openlldp will try to max out on the verify time. Hence the -ERANGE.

The range I chose for the policy comes from 802.3-2018 clause 30.14.1.6,
which says that the aMACMergeVerifyTime variable has a range between 1
and 128 ms inclusive.