netdev - Re: [RESEND PATCH net-next v5 2/2] net: phy: dp83869: Add speed optimization feature

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Date:   Mon, 28 Sep 2020 21:34:12 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Dan Murphy <dmurphy@...com>
Cc:     davem@...emloft.net, f.fainelli@...il.com, hkallweit1@...il.com,
        mkubecek@...e.cz, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH net-next v5 2/2] net: phy: dp83869: Add speed
 optimization feature

On Mon, Sep 28, 2020 at 09:51:35AM -0500, Dan Murphy wrote:
> Set the speed optimization bit on the DP83869 PHY.
> 
> Speed optimization, also known as link downshift, enables fallback to 100M
> operation after multiple consecutive failed attempts at Gigabit link
> establishment. Such a case could occur if cabling with only four wires
> (two twisted pairs) were connected instead of the standard cabling with
> eight wires (four twisted pairs).
> 
> The number of failed link attempts before falling back to 100M operation is
> configurable. By default, four failed link attempts are required before
> falling back to 100M.
> 
> Signed-off-by: Dan Murphy <dmurphy@...com>

Reviewed-by: Andrew Lunn <andrew@...n.ch>

> +	default:
> +		phydev_err(phydev,
> +			   "Downshift count must be 1, 2, 4 or 8\n");
> +		return -EINVAL;
> +	}

At some point it would be good to plumb in extack so we could return
this to user space.

     Andrew