linux-kernel - Re: [RFC PATCH 1/2] net: phy: dp83867: add w/a for packet errors seen with short cables

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Date:   Tue, 25 Apr 2023 14:05:34 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Siddharth Vadapalli <s-vadapalli@...com>
Cc:     hkallweit1@...il.com, linux@...linux.org.uk, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, srk@...com
Subject: Re: [RFC PATCH 1/2] net: phy: dp83867: add w/a for packet errors
 seen with short cables

On Tue, Apr 25, 2023 at 11:14:28AM +0530, 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.
> 
> Signed-off-by: Grygorii Strashko <grygorii.strashko@...com>
> Signed-off-by: Siddharth Vadapalli <s-vadapalli@...com>

https://www.kernel.org/doc/html/latest/process/maintainer-netdev.html

Please set the tree in the Subject line to be net.
Please also add a Fixes: tag, probably for the patch which added this driver.




> ---
>  drivers/net/phy/dp83867.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/phy/dp83867.c b/drivers/net/phy/dp83867.c
> index 5821f04c69dc..ba60cf35872e 100644
> --- a/drivers/net/phy/dp83867.c
> +++ b/drivers/net/phy/dp83867.c
> @@ -42,6 +42,7 @@
>  #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
> @@ -934,8 +935,20 @@ 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;
> +
> +	phy_write_mmd(phydev, DP83867_DEVADDR, DP83867_DSP_FFE_CFG, 0X0E81);

Maybe check the return code for errors?

      Andrew