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 10:19:45 +0100
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: esben@...nix.com, Conor Dooley <conor@...nel.org>
Cc: 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

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.

> 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...

Best regards,
Krzysztof