linux-kernel - Re: [RFC PATCH 2/9] dt-bindings: arm: amlogic: add X96-AIR bindings

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Message-ID: <b3307dfd-962c-73bb-1712-8dbbf977b6f5@baylibre.com>
Date:   Wed, 8 Dec 2021 09:17:49 +0100
From:   Neil Armstrong <narmstrong@...libre.com>
To:     Christian Hewitt <christianshewitt@...il.com>,
        Rob Herring <robh@...nel.org>
Cc:     Mark Rutland <mark.rutland@....com>,
        Kevin Hilman <khilman@...libre.com>,
        devicetree <devicetree@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org,
        LKML <linux-kernel@...r.kernel.org>,
        Benoit Masson <yahoo@...enite.com>
Subject: Re: [RFC PATCH 2/9] dt-bindings: arm: amlogic: add X96-AIR bindings

On 08/12/2021 05:44, Christian Hewitt wrote:
> 
>> On 8 Dec 2021, at 1:21 am, Rob Herring <robh@...nel.org> wrote:
>>
>> On Tue, Nov 30, 2021 at 06:05:16AM +0000, Christian Hewitt wrote:
>>> Add board bindings for the Amediatech X96-AIR STB which ships with
>>> model variants distiguished by Ethernet configuration: models using
>>> internal 10/100 PHY have a -100 suffix, while models using external
>>> Gigabit PHY have a -1000 suffix.
>>
>> Isn't the phy described in DT? Why do you need to describe this 1 
>> difference at the top level?

The difference is between internal VS external PHY, which means
difference in pinmuxing & settings for the MDIO mux selecting the
PHY interface.

The other issue is about the bootloader, the vendor bootloader is not
necessarily capable of detecting the PHY type, and correctly altering
the DT without a complex script.

Having a single DT adds a dependency on the bootloader, which for me isn't
acceptable.

Neil

> 
> Users who purchase Android STBs as a cheap Linux media device (or are
> reimiaging an existing device when they give up on Android) generally
> have no idea what a PHY is, so reading a device-tree file to pick the
> correct one is beyond them. Most people blindly try all dtb files for
> a class of device until they find one that works, so top-level naming
> is simply to hint the process and reduce guesswork. It’s not perfect,
> but it does appear to reduce the quantity of “Ethernet doesn’t work!”
> posts seen in support forums.
> 
> Christian
> 
>>> Signed-off-by: Christian Hewitt <christianshewitt@...il.com>
>>> ---
>>> Documentation/devicetree/bindings/arm/amlogic.yaml | 2 ++
>>> 1 file changed, 2 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/arm/amlogic.yaml b/Documentation/devicetree/bindings/arm/amlogic.yaml
>>> index 36081734f720..e9ab0ffe8be7 100644
>>> --- a/Documentation/devicetree/bindings/arm/amlogic.yaml
>>> +++ b/Documentation/devicetree/bindings/arm/amlogic.yaml
>>> @@ -170,6 +170,8 @@ properties:
>>>       - description: Boards with the Amlogic Meson SM1 S905X3/D3/Y3 SoC
>>>         items:
>>>           - enum:
>>> +              - amediatech,x96-air-100
>>> +              - amediatech,x96-air-1000
>>>               - bananapi,bpi-m5
>>>               - hardkernel,odroid-c4
>>>               - hardkernel,odroid-hc4
>>> -- 
>>> 2.17.1
>>>
>>>
>