[U-Boot] [PATCH v4 4/5] doc: bindings: add mdio-handle property to ethernet nodes

[Alexandru Marginean]

On 11/18/2019 8:11 PM, Grygorii Strashko wrote:
> 
> 
> On 14/11/2019 17:04, Alex Marginean wrote:
>> Adds an optional mdio-handle property which identifies a MDIO bus 
>> which can
>> be scanned to find the relevant PHY.  The property is ignored if 
>> phy-handle
>> is also present.
>>
>> Signed-off-by: Alex Marginean <alexandru.marginean at nxp.com>
>> ---
>>   doc/device-tree-bindings/net/ethernet.txt | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/doc/device-tree-bindings/net/ethernet.txt 
>> b/doc/device-tree-bindings/net/ethernet.txt
>> index 3fc360523b..9f9629f8d6 100644
>> --- a/doc/device-tree-bindings/net/ethernet.txt
>> +++ b/doc/device-tree-bindings/net/ethernet.txt
>> @@ -9,6 +9,8 @@ The following properties are common to the Ethernet 
>> controllers:
>>   - max-speed: number, specifies maximum speed in Mbit/s supported by 
>> the device;
>>   - max-frame-size: number, maximum transfer unit (IEEE defined MTU), 
>> rather than
>>     the maximum frame size (there's contradiction in ePAPR).
>> +- mdio-handle: phandle, specifies a reference to a MDIO bus to be 
>> scanned to
>> +  find the PHY device.  Ignored if phy-handle is also present.
> 
> Sry, but it looks redundant. The Ethernet-controller bindings
> expects to use phy-handle which, in turn, allows to get MDIO node.

The problem I'm trying to solve is not that I don't want to get the
parent MDIO bus of a PHY referenced though phy-handle, but rather that I
want to avoid having a specific U-Boot DT for each PHY plug-in card that
could be used in our systems.  I'll explain that in more detail.

We have these QDS systems which support plug-in cards with PHYs on them.
The way it works is that a given ethernet interface is associated with
one of the QDS slots that should contain a plug-in card.  Each of the
slots has a MDIO bus associated with it, this bus is accessed through a
MDIO MUX on the QDS board.
The slot may be populated with one of several types of cards, which
are different designs, have different types of PHYs and more importantly
use different PHY addresses on the MDIO bus.

So now the summary is that an Ethernet interface is associated with a
MDIO bus that could be scanned to find the relevant PHY, while using the
existing phy-handle binding requires that U-Boot DT is edited whenever
a different card is plugged in, which is not practical and avoidable.

> 
> So, if your platform is DT based and can use DT then it's reasonable to 
> follow standard binding,
> which, in addition, allows to specify Ethernet PHY properties.

Sure, and we do that on boards and for PHYs which are at fixed addresses
on MDIO bus, but that is impractical with the swappable cards.

> More over, your series does not provide user for this new property.

That's true, I was planning to send the QDS DT after this was merged,
but if it helps I can add it to this patch set.

Alex

> Personally I do not see even reasons to have 
> doc/device-tree-bindings/net/ethernet.txt in u-boot
> and think we should follow [1]
> 
>>   - phy-mode: string, operation mode of the PHY interface; supported 
>> values are
>>     "mii", "gmii", "sgmii", "qsgmii", "tbi", "rev-mii", "rmii", 
>> "rgmii", "rgmii-id",
>>     "rgmii-rxid", "rgmii-txid", "rtbi", "smii", "xgmii"; this is now a 
>> de-facto
>>
> 
> [1] 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/net/ethernet-controller.yaml 
> 
>