linux-kernel - Re: [PATCH net v2] net: phy: dp83867: add w/a for packet errors seen with short cables

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Message-ID: <7a53f0d3-3e9a-4024-6b19-72ad9c19ab97@gmail.com>
Date:   Tue, 9 May 2023 10:59:38 +0200
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Siddharth Vadapalli <s-vadapalli@...com>, andrew@...n.ch,
        linux@...linux.org.uk, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, srk@...com
Subject: Re: [PATCH net v2] net: phy: dp83867: add w/a for packet errors seen
 with short cables

On 09.05.2023 07:21, Siddharth Vadapalli wrote:
> From: Grygorii Strashko <grygorii.strashko@...com>
> 
> Introduce the W/A for packet errors seen with short cables (<1m) between
> two DP83867 PHYs.
> 
> The W/A recommended by DM requires FFE Equalizer Configuration tuning by
> writing value 0x0E81 to DSP_FFE_CFG register (0x012C), surrounded by hard
> and soft resets as follows:
> 
> write_reg(0x001F, 0x8000); //hard reset
> write_reg(DSP_FFE_CFG, 0x0E81);
> write_reg(0x001F, 0x4000); //soft reset
> 
> Since  DP83867 PHY DM says "Changing this register to 0x0E81, will not
> affect Long Cable performance.", enable the W/A by default.
> 
> Fixes: 2a10154abcb7 ("net: phy: dp83867: Add TI dp83867 phy")
> Signed-off-by: Grygorii Strashko <grygorii.strashko@...com>
> Signed-off-by: Siddharth Vadapalli <s-vadapalli@...com>
> ---
> 
> V1 patch at:
> https://lore.kernel.org/r/20230508070019.356548-1-s-vadapalli@ti.com
> 
> Changes since v1 patch:
> - Wrap the line invoking phy_write_mmd(), limiting it to 80 characters.
> - Replace 0X0E81 with 0x0e81 in the call to phy_write_mmd().
> - Replace 0X012C with 0x012c in the new define for DP83867_DSP_FFE_CFG.
> 
> RFC patch at:
> https://lore.kernel.org/r/20230425054429.3956535-2-s-vadapalli@ti.com/
> 
> Changes since RFC patch:
> - Change patch subject to PATCH net.
> - Add Fixes tag.
> - Check return value of phy_write_mmd().
> 
>  drivers/net/phy/dp83867.c | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/phy/dp83867.c b/drivers/net/phy/dp83867.c
> index d75f526a20a4..bbdcc595715d 100644
> --- a/drivers/net/phy/dp83867.c
> +++ b/drivers/net/phy/dp83867.c
> @@ -44,6 +44,7 @@
>  #define DP83867_STRAP_STS1	0x006E
>  #define DP83867_STRAP_STS2	0x006f
>  #define DP83867_RGMIIDCTL	0x0086
> +#define DP83867_DSP_FFE_CFG	0x012c
>  #define DP83867_RXFCFG		0x0134
>  #define DP83867_RXFPMD1	0x0136
>  #define DP83867_RXFPMD2	0x0137
> @@ -941,8 +942,23 @@ static int dp83867_phy_reset(struct phy_device *phydev)
>  
>  	usleep_range(10, 20);
>  
> -	return phy_modify(phydev, MII_DP83867_PHYCTRL,
> +	err = phy_modify(phydev, MII_DP83867_PHYCTRL,
>  			 DP83867_PHYCR_FORCE_LINK_GOOD, 0);
> +	if (err < 0)
> +		return err;
> +

Would be good to add a comment here explaining what this magic write does.

> +	err = phy_write_mmd(phydev, DP83867_DEVADDR, DP83867_DSP_FFE_CFG,
> +			    0x0e81);
> +	if (err < 0)
> +		return err;
> +
> +	err = phy_write(phydev, DP83867_CTRL, DP83867_SW_RESTART);
> +	if (err < 0)
> +		return err;
> +
> +	usleep_range(10, 20);
> +
> +	return 0;
>  }
>  
>  static void dp83867_link_change_notify(struct phy_device *phydev)