linux-kernel - Re: [PATCH 2/3] dt-bindings: net: snps,dwmac: Add time-based-scheduling property

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Date: Thu, 25 Jan 2024 12:55:12 +0100
From: esben@...nix.com
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc: Conor Dooley <conor@...nel.org>,  devicetree@...r.kernel.org,  "David S.
 Miller" <davem@...emloft.net>,  Eric Dumazet <edumazet@...gle.com>,  Jakub
 Kicinski <kuba@...nel.org>,  Paolo Abeni <pabeni@...hat.com>,  Rob Herring
 <robh+dt@...nel.org>,  Krzysztof Kozlowski
 <krzysztof.kozlowski+dt@...aro.org>,  Conor Dooley <conor+dt@...nel.org>,
  Alexandre Torgue <alexandre.torgue@...s.st.com>,  Giuseppe Cavallaro
 <peppe.cavallaro@...com>,  Jose Abreu <joabreu@...opsys.com>,
  netdev@...r.kernel.org,  linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] dt-bindings: net: snps,dwmac: Add
 time-based-scheduling property

Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org> writes:

> On 25/01/2024 10:10, esben@...nix.com wrote:
>> Conor Dooley <conor@...nel.org> writes:
>> 
>>> On Wed, Jan 24, 2024 at 03:33:06PM +0100, Esben Haabendal wrote:
>>>> Time Based Scheduling can be enabled per TX queue, if supported by the
>>>> controller.
>>>
>>> If time based scheduling is not supported by the controller, then the
>>> property should not be present! The presence of a property like this
>>> should mean that the feature is supported, using it is up to the
>>> operating system.
>>>
>>> That said, why is this a property that should be in DT?
>> 
>> It is added to the tx-queues-config object of snps,dwmac bindings. This
>> entire object is about configuration of the ethernet controller, which
>> is also what the purpose of the snps,time-based-scheduling.
>> So yes, it is not specifically about describing what the hardware is
>> capable of, but how the hardware is configured. It is a continuation of
>> the current driver design.
>> 
>>> If support is per controller is it not sufficient to use the
>>> compatible to determine if this is supported?
>> 
>> Are you suggesting to include the mapping from all supported compatible
>> controllers to which TX queues supports TBS in the driver code?  What
>> would the benefit of that compared to describing it explicitly in the
>> binding?
>
> The benefit is complying with DT bindings rules, saying that bindings
> describe hardware pieces, not drivers.

Understood.

>> And for the purpose of the above question, I am talking about it as if
>> the binding was describing the hardware capability and not the
>> configuration.
>
> "if"? You wrote it is for driver design...

If you look at the current driver, all the devicetree bindings under
rx-queues-config and tx-queues-config are violating the DT binding
rules.
Cleaning up that requires quite some work and I guess will break
backwards compatibility to some extend.

But that is another story.

I will respin the patch according to Conor's suggestion.

/Esben