netdev - Re: [PATCH] DSA support for Micrel KSZ8895

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Date:   Mon, 28 Aug 2017 08:47:12 +0200
From:   Pavel Machek <pavel@....cz>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Woojung.Huh@...rochip.com, nathan.leigh.conrad@...il.com,
        vivien.didelot@...oirfairelinux.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Tristram.Ha@...rel.com,
        andrew@...n.ch
Subject: Re: [PATCH] DSA support for Micrel KSZ8895

Hi!

> >No, tag_ksz part probably is not acceptable. Do you see solution
> >better than just copying it into tag_ksz1 file?
> 
> You could have all Micrel tag implementations live under net/dsa/tag_ksz.c and have e.g: DSA_TAG_PROTO_KSZ for the current (newer) switches and DSA_TAG_PROTO_KSZ_LEGACY (or any other name) for the older switches and you would provide two sets of function pointers depending on which protocol is requested by the switch.
> 
> Considering the minor difference needed in tagging here, it might be acceptable to actually keep the current functions and just have the xmit() call check what get_tag_protocol returns and use word 1 or 0 based on that. Even though that's a fast path it shouldn't hurt performance too much. If it does, we can always copy the tagging protocol into dsa_slave_priv so you have a fast access to it.
> 

Actually I believe I can do optimizer tricks to keep this zero-cost
with clean code, if needed.

> >
> >Any more comments, etc?
> 
> The MII emulation bits are interesting, was it not sufficient if you implemented phy_read and phy_write operations that perform the necessary internal PHY accesses or maybe you don't get access to standard MII registers? b53 does such a thing and we merely just need to do a simple shift to access the MII register number, thus avoiding the translation.
> 

We don't get standard MII registers over SPI bus.

> >Help would be welcome.
> 
> I concur with Andrew, try to get a patch series, even an RFC one together so we can review things individually. 
> 
> How functional is your driver so far? I'd say the basic stuff to get working: counters (debugging), link management (auto-negotiation, forced, etc.) and basic bridging: all ports separate by default and working port to port switching when brought together in a bridge. VLAN, FDB, MDB, other ethtool goodies can be added later on.
>

Which counters are essential? Link management and basic bridging
should work, not sure if I'll have time to do more than that.

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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