netdev - Re: [PATCH 4/4] amd-xgbe: Fix network fluctuations when using 1G BELFUSE SFP

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Message-ID: <4e899509-baa1-25be-b216-10c2b2ad047d@gmail.com>
Date:   Fri, 12 Feb 2021 22:14:45 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Shyam Sundar S K <Shyam-sundar.S-k@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org
Cc:     Sudheesh.Mavila@....com
Subject: Re: [PATCH 4/4] amd-xgbe: Fix network fluctuations when using 1G
 BELFUSE SFP

On 12.02.2021 19:00, Shyam Sundar S K wrote:
> Frequent link up/down events can happen when a Bel Fuse SFP part is
> connected to the amd-xgbe device. Try to avoid the frequent link
> issues by resetting the PHY as documented in Bel Fuse SFP datasheets.
> 
> Signed-off-by: Sudheesh Mavila <sudheesh.mavila@....com>
> Signed-off-by: Shyam Sundar S K <Shyam-sundar.S-k@....com>
> ---
>  drivers/net/ethernet/amd/xgbe/xgbe-phy-v2.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/net/ethernet/amd/xgbe/xgbe-phy-v2.c b/drivers/net/ethernet/amd/xgbe/xgbe-phy-v2.c
> index 1bb468ac9635..e328fd9bd294 100644
> --- a/drivers/net/ethernet/amd/xgbe/xgbe-phy-v2.c
> +++ b/drivers/net/ethernet/amd/xgbe/xgbe-phy-v2.c
> @@ -922,6 +922,12 @@ static bool xgbe_phy_belfuse_phy_quirks(struct xgbe_prv_data *pdata)
>  	if ((phy_id & 0xfffffff0) != 0x03625d10)
>  		return false;
>  
> +	/* Reset PHY - wait for self-clearing reset bit to clear */
> +	reg = phy_read(phy_data->phydev, 0x00);
> +	phy_write(phy_data->phydev, 0x00, reg | 0x8000);
> +	read_poll_timeout(phy_read, reg, !(reg & 0x8000) || reg < 0,
> +			  10000, 50000, true, phy_data->phydev, 0x0);
> +

Why don't you simply use genphy_soft_reset() ?
Also it's not too nice to use magic register and bit numbers,
there are constants available, e.g. 0x00 = MII_BMCR

>  	/* Disable RGMII mode */
>  	phy_write(phy_data->phydev, 0x18, 0x7007);
>  	reg = phy_read(phy_data->phydev, 0x18);
>