netdev - Re: [PATCH v2 3/4] net: ethernet: nb8800: Fix RGMII TX clock delay setup

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Message-ID: <yw1xpoctq34z.fsf@mansr.com>
Date:   Fri, 21 Jul 2017 15:24:28 +0100
From:   Måns Rullgård <mans@...sr.com>
To:     Marc Gonzalez <marc_gonzalez@...madesigns.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Martin Blumenstingl <martin.blumenstingl@...il.com>,
        Grygorii Strashko <grygorii.strashko@...com>,
        Fabio Estevam <fabio.estevam@....com>,
        Zefir Kurtisi <zefir.kurtisi@...atec.com>,
        Timur Tabi <timur@...eaurora.org>,
        Daniel Mack <zonque@...il.com>,
        netdev <netdev@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "David S. Miller" <davem@...emloft.net>,
        Thibaud Cornic <thibaud_cornic@...madesigns.com>,
        Mason <slash.tmp@...e.fr>
Subject: Re: [PATCH v2 3/4] net: ethernet: nb8800: Fix RGMII TX clock delay setup

Marc Gonzalez <marc_gonzalez@...madesigns.com> writes:

> On 21/07/2017 15:47, Måns Rullgård wrote:
>
>> Marc Gonzalez wrote:
>> 
>>> On 21/07/2017 15:04, Måns Rullgård wrote:
>>>
>>>> Marc Gonzalez wrote:
>>>>
>>>>> According to commit e5f3a4a56ce2a707b2fb8ce37e4414dcac89c672
>>>>> ("Documentation: devicetree: clarify usage of the RGMII phy-modes")
>>>>> there are 4 RGMII modes to handle:
>>>>>
>>>>> "rgmii" (RX and TX delays are added by the MAC when required)
>>>>> "rgmii-id" (RGMII with internal RX and TX delays provided by the PHY,
>>>>> 	the MAC should not add the RX or TX delays in this case)
>>>>> "rgmii-rxid" (RGMII with internal RX delay provided by the PHY,
>>>>> 	the MAC should not add an RX delay in this case)
>>>>> "rgmii-txid" (RGMII with internal TX delay provided by the PHY,
>>>>> 	the MAC should not add an TX delay in this case)
>>>>>
>>>>> Add TX delay in the MAC only for rgmii and rgmii-rxid.
>>>>>
>>>>> Signed-off-by: Marc Gonzalez <marc_gonzalez@...madesigns.com>
>>>>> ---
>>>>>  drivers/net/ethernet/aurora/nb8800.c | 6 ++++--
>>>>>  1 file changed, 4 insertions(+), 2 deletions(-)
>>>>>
>>>>> diff --git a/drivers/net/ethernet/aurora/nb8800.c b/drivers/net/ethernet/aurora/nb8800.c
>>>>> index ded041dbafe7..f3ed320eb4ad 100644
>>>>> --- a/drivers/net/ethernet/aurora/nb8800.c
>>>>> +++ b/drivers/net/ethernet/aurora/nb8800.c
>>>>> @@ -1268,11 +1268,13 @@ static int nb8800_tangox_init(struct net_device *dev)
>>>>>  		break;
>>>>>
>>>>>  	case PHY_INTERFACE_MODE_RGMII:
>>>>> -		pad_mode = PAD_MODE_RGMII;
>>>>> +	case PHY_INTERFACE_MODE_RGMII_RXID:
>>>>> +		pad_mode = PAD_MODE_RGMII | PAD_MODE_GTX_CLK_DELAY;
>>>>>  		break;
>>>>>
>>>>> +	case PHY_INTERFACE_MODE_RGMII_ID:
>>>>>  	case PHY_INTERFACE_MODE_RGMII_TXID:
>>>>> -		pad_mode = PAD_MODE_RGMII | PAD_MODE_GTX_CLK_DELAY;
>>>>> +		pad_mode = PAD_MODE_RGMII;
>>>>>  		break;
>>>>>
>>>>>  	default:
>>>>
>>>> I still don't like this.  Having both the MAC and PHY drivers react to
>>>> the phy-connection-type property is bound to cause trouble somewhere.
>>>>
>>>> The only way out of the current mess is to define new properties for
>>>> both MAC and PHY that override the existing ones if present.
>>>
>>> Do you mean defining 4 new bindings and their corresponding
>>> phy_interface_t enum values? For example:
>>>
>>> "rgmii-v2"
>>> "rgmii-id-v2"
>>> "rgmii-rxid-v2"
>>> "rgmii-txid-v2"
>>>
>>> 	PHY_INTERFACE_MODE_RGMII_V2,
>>> 	PHY_INTERFACE_MODE_RGMII_ID_V2,
>>> 	PHY_INTERFACE_MODE_RGMII_RXID_V2,
>>> 	PHY_INTERFACE_MODE_RGMII_TXID_V2,
>>>
>>> And then handling these new enums in the at803x and nb8800 drivers?
>> 
>> It has already been suggested to add new properties specifying desired
>> delays in picoseconds.  If present on the MAC node, the MAC driver
>> should attempt to provide the delay, and if present on the PHY node, the
>> PHY driver is responsible.
>
> Sorry, I had already forgotten about Florian's suggestion:
>> If you introduced PHY and/or MAC specific properties to configure the
>> delays in the appropriate unit of time (say ps), you could use a
>> non-compliant 'phy-mode' just to satisfy the driver/PHY library and
>> still override the delays you need.
>
> So we would need two properties (RX and TX).
> "rgmii_rx_skew_ps" and "rgmii_tx_skew_ps"
>
> but it's not clear to me how the MAC probe function communicates
> the arguments to the phy driver. Looks like we would need to add
> two fields to struct phy_device, and maybe define a new phy-mode
> to instruct the PHY driver to look for the two fields.

There's no need for the drivers to communicate.  The location of the
properties in the device tree determines which driver should deal with
it.

> I don't have time to work on that for now, but I do need to
> fix the nb8800 driver now. Can we apply the following patch
> in the interim?
>
> diff --git a/drivers/net/ethernet/aurora/nb8800.c b/drivers/net/ethernet/aurora/nb8800.c
> index ded041dbafe7..e94159507847 100644
> --- a/drivers/net/ethernet/aurora/nb8800.c
> +++ b/drivers/net/ethernet/aurora/nb8800.c
> @@ -1268,11 +1268,10 @@ static int nb8800_tangox_init(struct net_device *dev)
>                 break;
>
>         case PHY_INTERFACE_MODE_RGMII:
> -               pad_mode = PAD_MODE_RGMII;
> -               break;
> -
> +       case PHY_INTERFACE_MODE_RGMII_ID:
> +       case PHY_INTERFACE_MODE_RGMII_RXID:
>         case PHY_INTERFACE_MODE_RGMII_TXID:
> -               pad_mode = PAD_MODE_RGMII | PAD_MODE_GTX_CLK_DELAY;
> +               pad_mode = PAD_MODE_RGMII;
>                 break;
>
>         default:

Simply stop reacting to the delay aspect of the phy-connection-type
property?  Yes, I'm fine with that.

-- 
Måns Rullgård