From mboxrd@z Thu Jan  1 00:00:00 1970
From: Florian Fainelli <f.fainelli@gmail.com>
Subject: Re: [PATCH NET V5 1/2] net: phy: Add phy loopback support in net phy
 framework
Date: Mon, 26 Jun 2017 09:45:29 -0700
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To: Lin Yun Sheng <linyunsheng@huawei.com>, davem@davemloft.net,
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On 06/25/2017 07:10 PM, Lin Yun Sheng wrote:
> This patch add set_loopback in phy_driver, which is used by Mac
> driver to enable or disable a phy. it also add a generic
> genphy_loopback function, which use BMCR loopback bit to enable
> or disable a phy.
> 
> Signed-off-by: Lin Yun Sheng <linyunsheng@huawei.com>

Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>

[snip]

> +int phy_loopback(struct phy_device *phydev, bool enable)
> +{
> +	struct phy_driver *phydrv = to_phy_driver(phydev->mdio.dev.driver);
> +	int ret = 0;
> +
> +	mutex_lock(&phydev->lock);
> +
> +	if (enable && phydev->loopback_enabled) {
> +		ret = -EBUSY;
> +		goto out;
> +	}
> +
> +	if (!enable && !phydev->loopback_enabled) {
> +		ret = -EINVAL;
> +		goto out;
> +	}

I am not sure if it is necessary to treat that condition as an error,
but I guess why not.
-- 
Florian