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

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Message-ID: <20240125-pebble-reproach-f550d00a2abb@spud>
Date: Thu, 25 Jan 2024 17:14:55 +0000
From: Conor Dooley <conor@...nel.org>
To: esben@...nix.com
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.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

On Thu, Jan 25, 2024 at 12:55:12PM +0100, esben@...nix.com wrote:
> 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.

Let bygones be bygones. If something undesirable got in previously,
breaking backwards compatibility there is not justified IMO.

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