netdev - Re: [PATCH 2/2] net: ethernet: nb8800: Fix RGMII TX clock delay setup

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Date:   Wed, 19 Jul 2017 19:36:43 +0200
From:   Mason <slash.tmp@...e.fr>
To:     Mans Rullgard <mans@...sr.com>
Cc:     Marc Gonzalez <marc_gonzalez@...madesigns.com>,
        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>
Subject: Re: [PATCH 2/2] net: ethernet: nb8800: Fix RGMII TX clock delay setup

On 19/07/2017 19:17, Måns Rullgård wrote:

> Marc Gonzalez writes:
> 
>> According to commit e5f3a4a56ce2a707b2fb8ce37e4414dcac89c672
>> ("Documentation: devicetree: clarify usage of the RGMII phy-modes")
>> there are 4 RGMII phy-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)
>>
>> Let the MAC handle TX clock delay for rgmii and rgmii-rxid.
>>
>> Signed-off-by: Marc Gonzalez <marc_gonzalez@...madesigns.com>
>> ---
>>  drivers/net/ethernet/aurora/nb8800.c | 8 +++++---
>>  1 file changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/aurora/nb8800.c b/drivers/net/ethernet/aurora/nb8800.c
>> index 041cfb7952f8..f3ed320eb4ad 100644
>> --- a/drivers/net/ethernet/aurora/nb8800.c
>> +++ b/drivers/net/ethernet/aurora/nb8800.c
>> @@ -609,7 +609,7 @@ static void nb8800_mac_config(struct net_device *dev)
>>  		mac_mode |= HALF_DUPLEX;
>>
>>  	if (gigabit) {
>> -		if (priv->phy_mode == PHY_INTERFACE_MODE_RGMII)
>> +		if (phy_interface_is_rgmii(dev->phydev))
>>  			mac_mode |= RGMII_MODE;
>>
>>  		mac_mode |= GMAC_MODE;
> 
> This is a separate issue, and the change is obviously correct.
> 
>> @@ -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;
> 
> Won't this just make it break in a different set of circumstances?

I don't think so, and here's my reasoning:

AFAIU, the HW block always requires a TX clock delay
(I don't know what the "safe" interval is. PHY adds
2.4 ns, MAC adds ~1 ns, both work.)
RX clock delay seems to be "Don't Care" (tested both
enabled and disabled by PHY)
By "tested", I mean ability to ping remote system.

If phy-mode is RGMII or RGMII_RXID, then don't add
TX clock delay from PHY, therefore add it from MAC.

If phy_mode is RGMII_ID or RGMII_TXID, then do add
TX clock delay from PHY, therefore don't add it from MAC.

What set of circumstances would create an issue?

Regards.