netdev - Re: [PATCH v4 net-next 5/9] net: dsa: lantiq_gswip: serialize access to the PCE table

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Date:   Sat, 23 Oct 2021 17:07:49 +0200
From:   Hauke Mehrtens <hauke@...ke-m.de>
To:     Vladimir Oltean <vladimir.oltean@....com>, netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        UNGLinuxDriver@...rochip.com, DENG Qingfang <dqfext@...il.com>,
        Kurt Kanzenbach <kurt@...utronix.de>,
        Woojung Huh <woojung.huh@...rochip.com>,
        Sean Wang <sean.wang@...iatek.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        George McCollister <george.mccollister@...il.com>,
        John Crispin <john@...ozen.org>,
        Aleksander Jan Bajkowski <olek2@...pl>,
        Egil Hjelmeland <privat@...l-hjelmeland.no>,
        Oleksij Rempel <o.rempel@...gutronix.de>,
        Prasanna Vengateshan <prasanna.vengateshan@...rochip.com>,
        Ansuel Smith <ansuelsmth@...il.com>,
        Alvin Šipraga <alsi@...g-olufsen.dk>,
        Claudiu Manoil <claudiu.manoil@....com>
Subject: Re: [PATCH v4 net-next 5/9] net: dsa: lantiq_gswip: serialize access
 to the PCE table

On 10/22/21 8:43 PM, Vladimir Oltean wrote:
> Looking at the code, the GSWIP switch appears to hold bridging service
> structures (VLANs, FDBs, forwarding rules) in PCE table entries.
> Hardware access to the PCE table is non-atomic, and is comprised of
> several register reads and writes.

The switch has multiple tables which can be accessed with indirect 
addressing over the PCE registers.

> These accesses are currently serialized by the rtnl_lock, but DSA is
> changing its driver API and that lock will no longer be held when
> calling ->port_fdb_add() and ->port_fdb_del().
> 
> So this driver needs to serialize the access to the PCE table using its
> own locking scheme. This patch adds that.

The driver also uses the gswip_pce_load_microcode() function to load a 
static configuration for the packet classification engine into a table 
using the same registers. It is currently not protected, but only called 
by the DSA setup callback.

> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> ---
> v3->v4: call mutex_init
> 
>   drivers/net/dsa/lantiq_gswip.c | 28 +++++++++++++++++++++++-----
>   1 file changed, 23 insertions(+), 5 deletions(-)
> 
Acked-by: Hauke Mehrtens <hauke@...ke-m.de>