linux-kernel - Re: [RFC PATCH v2 5/8] net: pcs: add driver for MediaTek USXGMII PCS

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Message-ID: <ZXC2MFn7pVX/KNmJ@shell.armlinux.org.uk>
Date:   Wed, 6 Dec 2023 17:58:08 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Maxime Chevallier <maxime.chevallier@...tlin.com>
Cc:     Daniel Golle <daniel@...rotopia.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Chunfeng Yun <chunfeng.yun@...iatek.com>,
        Vinod Koul <vkoul@...nel.org>,
        Kishon Vijay Abraham I <kishon@...nel.org>,
        Felix Fietkau <nbd@....name>, John Crispin <john@...ozen.org>,
        Sean Wang <sean.wang@...iatek.com>,
        Mark Lee <Mark-MC.Lee@...iatek.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Alexander Couzens <lynxis@...0.eu>,
        Qingfang Deng <dqfext@...il.com>,
        SkyLake Huang <SkyLake.Huang@...iatek.com>,
        Philipp Zabel <p.zabel@...gutronix.de>, netdev@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-phy@...ts.infradead.org
Subject: Re: [RFC PATCH v2 5/8] net: pcs: add driver for MediaTek USXGMII PCS

On Wed, Dec 06, 2023 at 10:58:38AM +0100, Maxime Chevallier wrote:
> On Wed, 6 Dec 2023 01:44:38 +0000
> Daniel Golle <daniel@...rotopia.org> wrote:
> > +	/* Read USXGMII link status */
> > +	state->link = FIELD_GET(RG_PCS_RX_LINK_STATUS,
> > +				mtk_r32(mpcs, RG_PCS_RX_STATUS0));
> > +
> > +	/* Continuously repeat re-configuration sequence until link comes up */
> > +	if (!state->link) {
> > +		mtk_usxgmii_pcs_config(pcs, mpcs->neg_mode,
> > +				       state->interface, NULL, false);
> > +		return;
> 
> .pcs_get_state() isn't called only for link state polling,but also when querying
> the link state from ethtool, from phylink_ethtool_ksettings_get().
> 
> As mtk_usxgmii_pcs_config triggers a pcs reset and reconfiguration, won't this disrupt
> the link ? 

Highly likely if there's a race, but note that mtk_usxgmii_pcs_config()
only gets called if the link is *down*. I guess some IPs need a bit of
kicking to work properly.

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