netdev - Re: [PATCH net-next v2 3/3] net: ethernet: fec: Allow the MDIO preamble to be disabled

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Date:   Fri, 17 Apr 2020 17:39:23 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Andrew Lunn <andrew@...n.ch>, David Miller <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        Heiner Kallweit <hkallweit1@...il.com>, fugang.duan@....com,
        Chris Healy <Chris.Healy@....aero>
Subject: Re: [PATCH net-next v2 3/3] net: ethernet: fec: Allow the MDIO
 preamble to be disabled

Hi Andrew,

On 4/17/2020 5:03 PM, Andrew Lunn wrote:
> An MDIO transaction normally starts with 32 1s as a preamble. However
> not all devices requires such a preamble. Add a device tree property
> which allows the preamble to be suppressed. This will half the size of
> the MDIO transaction, allowing faster transactions.
> 
> Suggested-by: Chris Healy <Chris.Healy@....aero>
> Signed-off-by: Andrew Lunn <andrew@...n.ch>
> ---
>   Documentation/devicetree/bindings/net/mdio.yaml | 4 ++++
>   drivers/net/ethernet/freescale/fec_main.c       | 9 ++++++++-
>   2 files changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/devicetree/bindings/net/mdio.yaml b/Documentation/devicetree/bindings/net/mdio.yaml
> index bcd457c54cd7..41ed4019f8ca 100644
> --- a/Documentation/devicetree/bindings/net/mdio.yaml
> +++ b/Documentation/devicetree/bindings/net/mdio.yaml
> @@ -43,6 +43,10 @@ properties:
>       description:
>         Desired MDIO bus clock frequency in Hz.
>   
> +  suppress-preamble:
> +        description: The 32 bit preamble should be suppressed.
> +        type: boolean

This is a property of the MDIO device node and the MDIO bus controller 
as well, so I would assume that it has to be treated a little it like 
the 'broken-turn-around' property and it would have to be a bitmask per 
MDIO device address that is set/clear depending on what the device 
support. If it is set for the device and your controller supports it, 
then you an suppress preamble.
-- 
Florian