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

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Message-ID: <CAGVrzca7v3FMg1QT+LFQkPOf-o33=U0zpv_t8tkBSrrY+L+6+g@mail.gmail.com>
Date:	Tue, 10 Dec 2013 09:23:48 -0800
From:	Florian Fainelli <f.fainelli@...il.com>
To:	Chen-Yu Tsai <wens@...e.org>
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

2013/12/9 Chen-Yu Tsai <wens@...e.org>:
> 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?

Not really no, in that case the MDIO bus is implicitely implemented as
part of the Ethernet MAC controller, this is just fine.

> 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?

Sure, that is what most Ethernet driver do actually. They register
their own MDIO bus and make sure PHYs get attached to it.

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

Sure, sounds good, thanks!
-- 
Florian
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