linux-kernel - Re: [PATCH 1/2] net: ethernet: nb8800: Do not apply TX delay at MAC level

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Date:   Fri, 4 Nov 2016 16:36:50 +0100
From:   Sebastian Frias <sf84@...oste.net>
To:     Måns Rullgård <mans@...sr.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, Mason <slash.tmp@...e.fr>,
        Andrew Lunn <andrew@...n.ch>
Subject: Re: [PATCH 1/2] net: ethernet: nb8800: Do not apply TX delay at MAC
 level

Hi Måns,

On 11/04/2016 04:18 PM, Måns Rullgård wrote:
> Sebastian Frias <sf84@...oste.net> writes:
> 
>> The delay can be applied at PHY or MAC level, but since
>> PHY drivers will apply the delay at PHY level when using
>> one of the "internal delay" declinations of RGMII mode
>> (like PHY_INTERFACE_MODE_RGMII_TXID), applying it again
>> at MAC level causes issues.
> 
> The Broadcom GENET driver does the same thing.
> 

Well, I don't know who uses that driver, or why they did it that way.

However, with the current code and DT bindings, if one requires
the delay, phy-connection-type="rgmii-txid" must be set.

But when doing so, both the Atheros 8035 and the Aurora NB8800 drivers
will apply the delay.

I think a better way of dealing with this is that both, PHY and MAC
drivers exchange information so that the delay is applied only once.

I can see how to do that in another patch set.

>> Signed-off-by: Sebastian Frias <sf84@...oste.net>
>> ---
>>  drivers/net/ethernet/aurora/nb8800.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/ethernet/aurora/nb8800.c b/drivers/net/ethernet/aurora/nb8800.c
>> index b59aa35..d2855c9 100644
>> --- a/drivers/net/ethernet/aurora/nb8800.c
>> +++ b/drivers/net/ethernet/aurora/nb8800.c
>> @@ -1282,7 +1282,7 @@ static int nb8800_tangox_init(struct net_device *dev)
>>  		break;
>>
>>  	case PHY_INTERFACE_MODE_RGMII_TXID:
>> -		pad_mode = PAD_MODE_RGMII | PAD_MODE_GTX_CLK_DELAY;
>> +		pad_mode = PAD_MODE_RGMII;
>>  		break;
>>
>>  	default:
>> -- 
>> 1.7.11.2
> 
> If this change is correct (and I'm not convinced it is), that case
> should be merged with the one above it and PHY_INTERFACE_MODE_RGMII_RXID
> added as well.
> 

I can do a single patch.

The reason I made two patches was that it was clear what this patch
does, i.e.: do not apply the delay at MAC level, and what the subsequent
patch does, i.e.: handle all RGMII declinations.

Best regards,

Sebastian