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Date:   Sat, 16 Mar 2019 00:14:06 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Jose Abreu <jose.abreu@...opsys.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Joao Pinto <joao.pinto@...opsys.com>
Subject: Re: [PATCH net] net: phy: Don't assume loopback is supported

On 14.03.2019 11:37, Jose Abreu wrote:
> Some PHYs may not support loopback mode so we need to check if register
> is read-only.
> 
As I read Clause 22 this is a mandatory feature, the related bit is
specified as R/W. Do you have an actual example of a PHY w/o loopback
mode that doesn't allow to change this bit?

> Fixes: f0f9b4ed2338 ("net: phy: Add phy loopback support in net phy framework")
> Signed-off-by: Jose Abreu <joabreu@...opsys.com>
> Cc: Andrew Lunn <andrew@...n.ch>
> Cc: Florian Fainelli <f.fainelli@...il.com>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Joao Pinto <joao.pinto@...opsys.com>
> ---
>  drivers/net/phy/phy_device.c | 20 ++++++++++++++++++--
>  1 file changed, 18 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
> index 49fdd1ee798e..a749639d98c3 100644
> --- a/drivers/net/phy/phy_device.c
> +++ b/drivers/net/phy/phy_device.c
> @@ -1918,8 +1918,24 @@ EXPORT_SYMBOL(genphy_resume);
>  
>  int genphy_loopback(struct phy_device *phydev, bool enable)
>  {
> -	return phy_modify(phydev, MII_BMCR, BMCR_LOOPBACK,
> -			  enable ? BMCR_LOOPBACK : 0);
> +	int ret;
> +
> +	ret = phy_modify(phydev, MII_BMCR, BMCR_LOOPBACK,
> +			 enable ? BMCR_LOOPBACK : 0);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = phy_read(phydev, MII_BMCR);
> +	if (ret < 0)
> +		return ret;
> +
> +	if (enable) {
> +		if (ret & BMCR_LOOPBACK)
> +			return 0;
> +		return -EOPNOTSUPP;
> +	}
> +
> +	return 0;
>  }
>  EXPORT_SYMBOL(genphy_loopback);
>  
> 

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