linux-kernel - Re: [RFC PATCH net-next v3 11/15] net: dsa: mt7530: skip locking if MDIO bus isn't present

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Message-ID: <022e2a44-31de-4667-9474-6a8518ca030a@lunn.ch>
Date:   Wed, 29 Mar 2023 18:39:03 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Daniel Golle <daniel@...rotopia.org>
Cc:     netdev@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Sean Wang <sean.wang@...iatek.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        DENG Qingfang <dqfext@...il.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Sam Shih <Sam.Shih@...iatek.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        John Crispin <john@...ozen.org>, Felix Fietkau <nbd@....name>
Subject: Re: [RFC PATCH net-next v3 11/15] net: dsa: mt7530: skip locking if
 MDIO bus isn't present

On Wed, Mar 29, 2023 at 04:59:47PM +0100, Daniel Golle wrote:
> As MT7530 and MT7531 internally use 32-bit wide registers, each access
> to any register of the switch requires several operations on the MDIO
> bus. Hence if there is congruent access, e.g. due to PCS or PHY
> polling, this can mess up and interfere with another ongoing register
> access sequence.
> 
> However, the MDIO bus mutex is only relevant for MDIO-connected
> switches. Prepare switches which have there registers directly mapped
> into the SoCs register space via MMIO which do not require such
> locking. There we can simply use regmap's default locking mechanism.
> 
> Hence guard mutex operations to only be performed in case of MDIO
> connected switches.
> 
> Signed-off-by: Daniel Golle <daniel@...rotopia.org>

Reviewed-by: Andrew Lunn <andrew@...n.ch>

    Andrew