netdev - Re: [PATCH v2 net 06/10] net: dsa: tag_ocelot: break circular dependency with ocelot switch lib driver

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Date:   Tue, 12 Oct 2021 14:32:11 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Vladimir Oltean <vladimir.oltean@....com>, netdev@...r.kernel.org,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>, Po Liu <po.liu@....com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        Michael Walle <michael@...le.cc>,
        Rui Sousa <rui.sousa@....com>, Yangbo Lu <yangbo.lu@....com>,
        Xiaoliang Yang <xiaoliang.yang_1@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        UNGLinuxDriver@...rochip.com
Subject: Re: [PATCH v2 net 06/10] net: dsa: tag_ocelot: break circular
 dependency with ocelot switch lib driver

On 10/12/21 4:40 AM, Vladimir Oltean wrote:
> As explained here:
> https://lore.kernel.org/netdev/20210908220834.d7gmtnwrorhharna@skbuf/
> DSA tagging protocol drivers cannot depend on symbols exported by switch
> drivers, because this creates a circular dependency that breaks module
> autoloading.
> 
> The tag_ocelot.c file depends on the ocelot_ptp_rew_op() function
> exported by the common ocelot switch lib. This function looks at
> OCELOT_SKB_CB(skb) and computes how to populate the REW_OP field of the
> DSA tag, for PTP timestamping (the command: one-step/two-step, and the
> TX timestamp identifier).
> 
> None of that requires deep insight into the driver, it is quite
> stateless, as it only depends upon the skb->cb. So let's make it a
> static inline function and put it in include/linux/dsa/ocelot.h, a
> file that despite its name is used by the ocelot switch driver for
> populating the injection header too - since commit 40d3f295b5fe ("net:
> mscc: ocelot: use common tag parsing code with DSA").
> 
> With that function declared as static inline, its body is expanded
> inside each call site, so the dependency is broken and the DSA tagger
> can be built without the switch library, upon which the felix driver
> depends.
> 
> Fixes: 39e5308b3250 ("net: mscc: ocelot: support PTP Sync one-step timestamping")
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>

Reviewed-by: Florian Fainelli <f.fainelli@...il.com>
-- 
Florian