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

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Date:   Fri, 04 Nov 2016 15:27:55 +0000
From:   Måns Rullgård <mans@...sr.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Sebastian Frias <sf84@...oste.net>,
        "David S. Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, Mason <slash.tmp@...e.fr>
Subject: Re: [PATCH 1/2] net: ethernet: nb8800: Do not apply TX delay at MAC level

Andrew Lunn <andrew@...n.ch> writes:

> On Fri, Nov 04, 2016 at 04:02:24PM +0100, Sebastian Frias wrote:
>> 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.

If this is correct, most of the PHY drivers are broken.

>> 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;
>
> How many boards use this Ethernet driver? How many boards are your
> potentially breaking, because they need this delay?
>
> I guess it is a small number, because doesn't it require the PHY is
> also broken, not adding a delay when it should?

What if the PHY doesn't have that option?

-- 
Måns Rullgård