netdev - Re: [PATCH net-next 5/6] net: dsa: realtek-smi: add rtl8365mb subdriver for RTL8365MB-VC

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Message-ID: <20211014070809.6ca397ce@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Thu, 14 Oct 2021 07:08:09 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Alvin Šipraga <ALSI@...g-olufsen.dk>
Cc:     Alvin Šipraga <alvin@...s.dk>,
        Linus Walleij <linus.walleij@...aro.org>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Rob Herring <robh+dt@...nel.org>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Michael Rasmussen <MIR@...g-olufsen.dk>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 5/6] net: dsa: realtek-smi: add rtl8365mb
 subdriver for RTL8365MB-VC

On Thu, 14 Oct 2021 12:44:37 +0000 Alvin Šipraga wrote:
> On 10/13/21 5:13 PM, Jakub Kicinski wrote:
> > On Wed, 13 Oct 2021 08:33:36 +0000 Alvin Šipraga wrote:  
> >> I implement the dsa_switch_ops callback .get_ethtool_stats, using an
> >> existing function rtl8366_get_ethtool_stats in the switch helper library
> >> rtl8366.c. It was my understanding that this is the correct way to
> >> expose counters within the DSA framework - please correct me if that is
> >> wrong.  
> > 
> > It's the legacy way, today we have a unified API for reporting those
> > stats so user space SW doesn't have to maintain a myriad string matches
> > to get to basic IEEE stats across vendors. Driver authors have a truly
> > incredible ability to invent their own names for standard stats. It
> > appears that your pick of names is also unique :)
> > 
> > It should be trivial to plumb the relevant ethtool_ops thru to
> > dsa_switch_ops if relevant dsa ops don't exist.
> > 
> > You should also populate correct stats in dsa_switch_ops::get_stats64
> > (see the large comment above the definition of struct
> > rtnl_link_stats64 for mapping). A word of warning there, tho, that
> > callback runs in an atomic context so if your driver needs to block it
> > has to read the stats periodically from a async work.  
> 
> OK, so just to clarify:
> 
> - get_ethtool_stats is deprecated - do not use

It can still be used, but standardized interfaces should be preferred
whenever possible, especially when appropriate uAPI already exists.

> - get_eth_{phy,mac,ctrl,rmon}_stats is the new API - add DSA plumbing 
> and use this

Yup.

> - get_stats64 orthogonal to ethtool stats but still important - use also 
> this

Yes, users should be able to depend on basic interface stats (packets,
bytes, crc errors) to be correct.

> For stats64 I will need to poll asynchronously - do you have any 
> suggestion for how frequently I should do that? I see one DSA driver 
> doing it every 3 seconds, for example.

3 sec seems fine.