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:   Wed, 26 Apr 2023 14:36:22 +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

> >> @@ -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?
> 
> The return value of phy_write_mmd() doesn't have to be checked since it will be
> zero for the following reasons:
> The dp83867 driver does not have a custom .write_mmd method. Also, the dp83867
> phy does not support clause 45. Due to this, within __phy_write_mmd(), the ELSE
> statement will be executed, which results in the return value being zero.

Interesting.

I would actually say __phy_write_mmd() is broken, and should be
returning what __mdiobus_write() returns.

You should assume it will get fixed, and check the return value. And
it does no harm to check the return value.

    Andrew