netdev - DSCP support for KSZ switches

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Message-ID: <ZfmJ-O8XMT8oO-TS@pengutronix.de>
Date: Tue, 19 Mar 2024 13:50:00 +0100
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Vladimir Oltean <olteanv@...il.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Andrew Lunn <andrew@...n.ch>
Cc: Woojung Huh <woojung.huh@...rochip.com>, UNGLinuxDriver@...rochip.com,
	netdev@...r.kernel.org
Subject: DSCP support for KSZ switches

Hello all,

I'm currently working on implementing DSCP support for the KSZ switch series.
My efforts have led to the successful implementation of several callbacks,
including:

port_get_default_prio()
port_set_default_prio()
port_get_dscp_prio()

However, I am facing challenges with port_add_dscp_prio() and
port_del_dscp_prio() due to the KSZ switches' limitations on per-port DSCP
configuration. Specifically, the KSZ hardware allows only enabling or disabling
DSCP as the source of internal priority on a per-port basis. Additionally, it
supports either global DSCP remapping or using a default mapping, where the
internal priority is derived from bits 5:3 of the DSCP field.

Given these constraints, my question revolves around the appropriate tools or
interfaces for managing DSCP settings on these devices. Should the
enabling/disabling of DSCP per port be managed through dcb or ethtool?
Furthermore, concerning the global DSCP mapping, would devlink be the suitable
choice for this task?

Best regards,
Oleksij
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