linux-kernel - Re: enetc: fix bitfields, we are clearing wrong bits

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Date:   Sun, 21 Mar 2021 19:44:19 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Pavel Machek <pavel@...x.de>
Cc:     kernel list <linux-kernel@...r.kernel.org>,
        Claudiu Manoil <claudiu.manoil@....com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org
Subject: Re: enetc: fix bitfields, we are clearing wrong bits

On Sun, Mar 21, 2021 at 05:25:00PM +0100, Pavel Machek wrote:
> Bitfield manipulation in enetc_mac_config() looks wrong. Fix
> it. Untested.
> 
> Signed-off-by: Pavel Machek (CIP) <pavel@...x.de>
> 
> diff --git a/drivers/net/ethernet/freescale/enetc/enetc_pf.c b/drivers/net/ethernet/freescale/enetc/enetc_pf.c
> index 224fc37a6757..b85079493933 100644
> --- a/drivers/net/ethernet/freescale/enetc/enetc_pf.c
> +++ b/drivers/net/ethernet/freescale/enetc/enetc_pf.c
> @@ -505,7 +505,7 @@ static void enetc_mac_config(struct enetc_hw *hw, phy_interface_t phy_mode)
>  	if (phy_interface_mode_is_rgmii(phy_mode)) {
>  		val = enetc_port_rd(hw, ENETC_PM0_IF_MODE);
>  		val &= ~ENETC_PM0_IFM_EN_AUTO;
> -		val &= ENETC_PM0_IFM_IFMODE_MASK;
> +		val &= ~ENETC_PM0_IFM_IFMODE_MASK;
>  		val |= ENETC_PM0_IFM_IFMODE_GMII | ENETC_PM0_IFM_RG;
>  		enetc_port_wr(hw, ENETC_PM0_IF_MODE, val);
>  	}
> 
> -- 
> DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
> HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

Fixes: c76a97218dcb ("net: enetc: force the RGMII speed and duplex instead of operating in inband mode")
Reviewed-by: Vladimir Oltean <vladimir.oltean@....com>

Note that for normal operation, the bug was inconsequential, due to the
fact that we write the IF_MODE register in two stages, first in
.phylink_mac_config (which incorrectly cleared out a bunch of stuff),
then we update the speed and duplex to the correct values in
.phylink_mac_link_up. Maybe loopback mode was broken.

Thanks!