Date:   Thu, 4 May 2017 11:21:29 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     icenowy@...c.io
Cc:     Andrew Lunn <andrew@...n.ch>, Rob Herring <robh+dt@...nel.org>,
        netdev@...r.kernel.org, devicetree@...r.kernel.org,
        linux-sunxi@...glegroups.com, Icenowy Zheng <icenowy@...c.xyz>
Subject: Re: [PATCH 2/4] dt-bindings: add binding for RTL8211E Ethernet PHY

On 05/04/2017 11:10 AM, icenowy@...c.io wrote:
> 在 2017-04-22 08:22，Florian Fainelli 写道：
>> On 04/21/2017 04:24 PM, Icenowy Zheng wrote:
>>> From: Icenowy Zheng <icenowy@...c.xyz>
>>>
>>> Some RTL8211E Ethernet PHY have an issue that needs a workaround
>>> indicated with device tree.
>>>
>>> Add the binding for a property that indicates this workaround.
>>>
>>> Signed-off-by: Icenowy Zheng <icenowy@...c.xyz>
>>> ---
>>>  .../devicetree/bindings/net/realtek,rtl8211e.txt   | 22
>>> ++++++++++++++++++++++
>>>  1 file changed, 22 insertions(+)
>>>  create mode 100644
>>> Documentation/devicetree/bindings/net/realtek,rtl8211e.txt
>>>
>>> diff --git
>>> a/Documentation/devicetree/bindings/net/realtek,rtl8211e.txt
>>> b/Documentation/devicetree/bindings/net/realtek,rtl8211e.txt
>>> new file mode 100644
>>> index 000000000000..c1913301bfe8
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/net/realtek,rtl8211e.txt
>>> @@ -0,0 +1,22 @@
>>> +Realtek RTL8211E Ethernet PHY
>>> +
>>> +One batch of RTL8211E is slight broken, that needs some special (and
>>> +full of magic numbers) tweaking in order to make GbE to operate
>>> properly.
>>> +The only well-known board that used the broken batch is Pine64+.
>>> +Configure it through an Ethernet OF device node.
>>> +
>>> +Optional properties:
>>> +
>>> +- realtek,disable-rx-delay:
>>> +  If set, RX delay will be completely disabled (according to
>>> Realtek). This
>>> +  will affect the performance on non-broken boards.
>>> +  default: do not disable RX delay.
>>
>> Please don't introduce custom properties to do that, instead correct
>> specify the "phy-mode" such that it is e.g: "rgmii-txid" which indicates
>> that there should be no RX internal delay, but a TX internal delay added
>> by the PHY.
> 
> Checked the document, the meaning of "rgmii-txid" is not correct here.
> 
> This doesn't effect the MAC, and the MAC should still add TX delay.
> 
> The definition of "rgmii-txid" in
> Documentation/devicetree/binding/net/ethernet.txt is "RGMII with
> internal TX delay provided by the PHY, the MAC should not add an TX delay
> in this case". However, this do not indicate that the MAC doesn't add TX
> delay; in fact that just totally disabled the PHY to provide the RX delay.
> MAC still should to add delay on both TX/RX, which is the semantic of
> standard "rgmii".
> 
> So I cannot used "rgmii-txid" here, but should continue to use this
> custom property.

This is absolutely not a correct understanding. The 'phy-mode' property
defines the contract between the MAC and PHY. It is defined from the
PHY's perspective of the delay, which means that the MAC has to either
also provide an adequate delay (RX or TX) or not (RX or TX). So if you
specified 'phy-mode' = "rgmii" this means that the MAC needs to adds the
TX and RX delay, so implcitly this means that your MAC operates in
"rgmii-id", if the property was defined from the perspective of the MAC,
which it is not.

Both the Ethernet PHY driver and the MAC driver need to take care of
adjusting the delays based on the phydev->interface value.

The property you are introducing here is absolutely not appropriate
because it is entirely redundant with what 'phy-mode' already defines,
except the latter also covers a lot more cases.
-- 
Florian

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