linux-kernel - Re: [PATCH 07/10] ARM: dts: sun7i: cubietruck: Enable the GMAC

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Date:	Tue, 10 Dec 2013 12:11:00 +0800
From:	Chen-Yu Tsai <wens@...e.org>
To:	Florian Fainelli <f.fainelli@...il.com>
Cc:	Giuseppe Cavallaro <peppe.cavallaro@...com>,
	netdev <netdev@...r.kernel.org>,
	Rob Herring <rob.herring@...xeda.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-sunxi <linux-sunxi@...glegroups.com>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Srinivas Kandagatla <srinivas.kandagatla@...com>
Subject: Re: [PATCH 07/10] ARM: dts: sun7i: cubietruck: Enable the GMAC

On Tue, Dec 10, 2013 at 1:48 AM, Florian Fainelli <f.fainelli@...il.com> wrote:
> 2013/12/8 Chen-Yu Tsai <wens@...e.org>:
>> Florian, Giuseppe:
>>
>> On Sat, Dec 7, 2013 at 9:57 AM, Florian Fainelli <f.fainelli@...il.com> wrote:
>>> 2013/12/6 Chen-Yu Tsai <wens@...e.org>:
>>>> On Sat, Dec 7, 2013 at 5:09 AM, Florian Fainelli <f.fainelli@...il.com> wrote:
>>>>> 2013/12/6 Chen-Yu Tsai <wens@...e.org>:
>>>>>> The CubieTruck uses the GMAC with an RGMII phy.
>>>>>>
>>>>>> Signed-off-by: Chen-Yu Tsai <wens@...e.org>
>>>>>> ---
>>>>>>  arch/arm/boot/dts/sun7i-a20-cubietruck.dts | 8 ++++++++
>>>>>>  1 file changed, 8 insertions(+)
>>>>>>
>>>>>> diff --git a/arch/arm/boot/dts/sun7i-a20-cubietruck.dts b/arch/arm/boot/dts/sun7i-a20-cubietruck.dts
>>>>>> index 8a1009d..af212a2 100644
>>>>>> --- a/arch/arm/boot/dts/sun7i-a20-cubietruck.dts
>>>>>> +++ b/arch/arm/boot/dts/sun7i-a20-cubietruck.dts
>>>>>> @@ -33,6 +33,14 @@
>>>>>>                         pinctrl-0 = <&uart0_pins_a>;
>>>>>>                         status = "okay";
>>>>>>                 };
>>>>>> +
>>>>>> +               gmac: ethernet@...50000 {
>>>>>> +                       pinctrl-names = "default";
>>>>>> +                       pinctrl-0 = <&gmac_pins_rgmii>;
>>>>>> +                       snps,phy-addr = <1>;
>>>>>
>>>>> What is this snps,phy-addr property? Why is not a standard device tree
>>>>> node for an Ethernet PHY node used?
>>>>
>>>> This property is implemented by stmmac and documented in the DT
>>>> bindings. stmmac has not been updated to use Ethernet PHY nodes.
>>>
>>> This driver property should be removed and deprecated since there is
>>> an ePAPR standardized Ethernet PHY node. What I am worried here is the
>>> loss of information, the standard Ethernet DT node allows to specify
>>> much more information (clause, maximum speed, compatible string
>>> etc...).
>>
>> Giuseppe, any thoughts on this?
>>
>>>> Removing this property will not affect the function of the driver.
>>>> The driver probes its MDIO bus and selects the lowest available
>>>> address if not specified.
>>>
>>> So if this is just giving the driver a hint on where to  probe for a
>>> PHY on the MDIO bus, then let's drop it and use the standard DT node
>>> no?
>>
>> Sure. I will remove it from the DT.
>>
>> The stmmac driver does not have a seperate MDIO bus driver, nor
>> does it support Ethernet PHY node bindings. So I will not add
>> a phy node at this moment.
>
> This will create needless churn in the DT if you do not do it now,
> worse actually, we switch from a DT which specifically described
> Ethernet PHY nodes properly to a version where it does, to ultimately
> a newer version which does.
>
> Considering that the absence of a "snps,phy-addr" property will still
> result in the MDIO bus to be probed, keeping the existing Ethernet PHY
> nodes, referencing them correclty with a "phy-handle" property, but
> having no explicit support for these in the driver will not result in
> a functional change, and will reduce the DT churn. Also, you could
> still sneak a patch in this patchset which parses the standard
> EThernet PHY node binding.

I see. Adding the PHY node should be no trouble at all.
Is there a requirement for a seperate mdio bus in the DT?
I do not see it in the ePAPR. The stmmac mdio is not a seperate
driver, as is for most network controllers I presume.
Would attaching the PHY nodes directly under the ethernet controller
suffice?

We can then introduce PHY node support to the driver and
remove the "snps,phy-addr" property at the same time.

ChenYu

>>
>>>>>> +                       phy-mode = "rgmii";
>>>>>
>>>>> Especially since you use the relatively standard "phy-mode" property here?
>>>>
>>>> Used as specified in stmmac DT bindings.
>>>
>>> That one is kind of okay because of_get_phy_mode() knows about it,
>>> even though ePAPR states this should be "phy-connection-type", so I am
>>> okay with keeping that one because current practice and helpers are
>>> here.
>>
>> It seems all ARM DTs currently use "phy-mode".
>
> Which is why I said "is kind of okay", but this is not what the
> standard came up with, ARM is not exactly the best DT-citizen out
> there as people are prone to making up new properties when the
> standard already defines some, anyway....
> --
> Florian
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