netdev - Re: [linux-sunxi] Re: [PATCH 2/4] dt-bindings: add binding for RTL8211E Ethernet PHY

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Message-ID: <068f1323-3864-620c-0deb-6c5e04a9e498@gmail.com>
Date:   Thu, 4 May 2017 11:29:23 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Icenowy Zheng <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: [linux-sunxi] Re: [PATCH 2/4] dt-bindings: add binding for
 RTL8211E Ethernet PHY

On 05/04/2017 11:26 AM, Icenowy Zheng wrote:
> 
> 
> 于 2017年5月5日 GMT+08:00 上午2:21:29, Florian Fainelli <f.fainelli@...il.com> 写到:
>> 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
> 
> The MAC doesn't lose its responsibility to tweak RX/TX delays with this property set.

No it does not but now there is no contract binding the MAC and the PHY
together was to what an appropriate delay configuration there should be.
This is why using phydev->interface (directly inherited from 'phy-mode')
is important because it binds the PHY and MAC on a contract.

> 
> This situation is that, the PHY's RX delay tweaking function is broken. But it doesn't mean that the PHY can take over *all* responsibility to tweak TX, it still needs MAC to tweak TX.

Correct, so what part of my answer was not clear in that sense?

> 
>> "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