linux-kernel - Re: [PATCH v3 02/12] powerpc: wiiu: device tree

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Date:   Wed, 29 Jun 2022 20:13:13 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Segher Boessenkool <segher@...nel.crashing.org>
Cc:     Ash Logan <ash@...quark.com>, krzysztof.kozlowski+dt@...aro.org,
        paulus@...ba.org, mpe@...erman.id.au, christophe.leroy@...roup.eu,
        robh+dt@...nel.org, benh@...nel.crashing.org,
        devicetree@...r.kernel.org, linkmauve@...kmauve.fr,
        linux-kernel@...r.kernel.org, rw-r-r-0644@...tonmail.com,
        joel@....id.au, linuxppc-dev@...ts.ozlabs.org, j.ne@...teo.net
Subject: Re: [PATCH v3 02/12] powerpc: wiiu: device tree

On 29/06/2022 18:13, Segher Boessenkool wrote:
> On Wed, Jun 29, 2022 at 11:58:18AM +0200, Krzysztof Kozlowski wrote:
>> On 28/06/2022 15:31, Ash Logan wrote:
>>> +	model = "nintendo,wiiu";
>>
>> It's not compatible, but user-visible string, e.g. "Nintendo Wii U"
> 
> The "model" property in OF is documented as:
> 
> ---
> “model”                                                                S
> Standard property name to define a manufacturer’s model number.
> 
> prop-encoded-array:
>   Text string, encoded with encode-string.
> A manufacturer-dependent string that generally specifies the model name
> and number (including revision level) for this device. The format of the
> text string is arbitrary, although in conventional usage the string
> begins with the name of the device’s manufacturer as with the “name”
> property.
> Although there is no standard interpretation for the value of the
> “model” property, a specific device driver might use it to learn, for
> instance, the revision level of its particular device.
> 
> See also: property, model.
> 
> Used as: " XYZCO,1416-02" encode-string " model" property

Hm, surprising to duplicate the compatible, but OK.

> ---
> 
>>> +	cpus {
>>> +		#address-cells = <1>;
>>> +		#size-cells = <0>;
>>> +
>>> +		/* TODO: Add SMP */
>>> +		PowerPC,espresso@0 {
>>
>> Node name should be generic, so "cpu". Unless something needs the
>> specific node name?
> 
> This is how most other PowerPC firmwares do it.  The PowerPC processor
> binding is older than the generic naming practice, so CPU nodes have
> device_type "cpu" instead.  

ePAPR 1.0 from 2008 explicitly asks for generic node names. So 4 years
before Nintento Wii U. Maybe earlier ePAPR-s were also asking for this,
no clue, don't have them.

> This is a required property btw, with that
> value.  (There is no requirement on the names of the CPU nodes).

That's fine, I am not talking about property.

> There is no added value in generic naming for CPU nodes anyway, since
> you just find them as the children of the "/cpus" node :-)

There is because you might have there caches. It also makes code easier
to read.

Best regards,
Krzysztof