netdev - Re: [PATCH v2] net/phy/vitesse: Configure RGMII skew on VSC8601, if needed

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Message-ID: <f05f5f5d-a010-def2-314a-09a859f9eda3@adaptrum.com>
Date:   Wed, 16 Nov 2016 08:44:30 -0800
From:   Alex <alex.g@...ptrum.com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     <f.fainelli@...il.com>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <davem@...emloft.net>,
        Gokhan Cosgul <gokhan@...ptrum.com>
Subject: Re: [PATCH v2] net/phy/vitesse: Configure RGMII skew on VSC8601, if
 needed



On 11/16/2016 05:50 AM, Andrew Lunn wrote:
> On Wed, Nov 16, 2016 at 01:02:33AM -0800, Alexandru Gagniuc wrote:
>> With RGMII, we need a 1.5 to 2ns skew between clock and data lines. The
>> VSC8601 can handle this internally. While the VSC8601 can set more
>> fine-grained delays, the standard skew settings work out of the box.
>> The same heuristic is used to determine when this skew should be enabled
>> as in vsc824x_config_init().
>>
>> +/* This adds a skew for both TX and RX clocks, so the skew should only be
>> + * applied to "rgmii-id" interfaces. It may not work as expected
>> + * on "rgmii-txid", "rgmii-rxid" or "rgmii" interfaces. */
>
> Hi Alexandru
>
> You should be able to make "rgmii" work as expected. If that is the
> phy mode, disable the skew.

And that's exactly the implemented behavior. See vsc8601_config_init() 
below.

Alex