netdev - Re: [PATCH net-next v5 1/2] dt-bindings: net: snps,dwmac: Tx queues with coe

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Date: Sun, 27 Aug 2023 03:18:03 +0300
From: Serge Semin <fancer.lancer@...il.com>
To: Rohan G Thomas <rohan.g.thomas@...el.com>
Cc: alexandre.torgue@...s.st.com, conor+dt@...nel.org, 
	conor.dooley@...rochip.com, davem@...emloft.net, devicetree@...r.kernel.org, 
	edumazet@...gle.com, joabreu@...opsys.com, krzysztof.kozlowski+dt@...aro.org, 
	kuba@...nel.org, linux-arm-kernel@...ts.infradead.org, 
	linux-kernel@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com, 
	mcoquelin.stm32@...il.com, netdev@...r.kernel.org, pabeni@...hat.com, 
	peppe.cavallaro@...com, robh+dt@...nel.org
Subject: Re: [PATCH net-next v5 1/2] dt-bindings: net: snps,dwmac: Tx queues
 with coe

On Thu, Aug 24, 2023 at 01:10:04AM +0800, Rohan G Thomas wrote:
> >On Tue, Aug 22, 2023 at 05:15:25PM -0700, Jakub Kicinski wrote:
> >> On Sat, 19 Aug 2023 10:31:31 +0800 Rohan G Thomas wrote:
> >> > +      snps,tx-queues-with-coe:
> >> > +        $ref: /schemas/types.yaml#/definitions/uint32
> >> > +        description: number of TX queues that support TX checksum offloading
> >> 
> >
> >> Is it going to be obvious that if not present all queues support
> >> checksum offload? I think we should document the default.
> >
> >This question is debatable:
> >1. By default the DW xGMAC and DW QoS Eth IP-cores are
> >synthesized with only the very first Tx queue having Tx COE enabled.
> >2. If TSO is disabled then the Tx COE can be individually enabled
> >for each queue available on DW QoS Eth controller and for the very
> >first N queues on DW xGMAC controller.
> >3. If TSO is enabled then the Tx COE will be automatically and always
> >enabled for as many first queues as there are TSO-capable
> >DMA-channels.
> >4. At the current state the STMMAC driver assumes that all Tx Queues
> >support Tx COE.
> >
> >The entry 4 can't be changed since we'll risk to catch regressions on
> >the platforms with no property specified. On the other hand it partly
> >contradicts to the rest of the entries. I don't know what would be a
> >correct way to specify the default value in this case. Most likely
> >just keep the entry 4 and be done with it.
> >
> >BTW I just noticed that but the suggested "snps,tx-queues-with-coe"
> >property semantic will only cover a DW XGMAC-part of the case 2. DW
> >QoS Eth can be synthesized with Tx COE individually enabled for a
> >particular queue if TSO is unavailable.
> 
> Hi Serge,
> 
> Didn't know about a different IP configuration supported by DW QoS Eth IP. If
> this is the case, I think we can have a flag 'coe-unsupported' for any TX
> queue subnode as below.
> 
> +          snps,coe-unsupported:

> +            $ref: /schemas/types.yaml#/definitions/flag

AFAIR tKrzysztof preferred to use type: boolean for the flags.

> +            description:
> +              TX checksum offload is unsupported by the TX queue. 

> +              If TX checksum
> +              offload is requested for a packet to be transmitted through this
> +              TX queue then have a software fallback in the driver for checksum
> +              calculation.

This is redundant in the HW description.

> 

> If this is okay, I can rework the patch based on this. Covers both DW QoS Eth IP
> and DW XGMAC IP cases.

I guess that's the only choice we have seeing the driver already
expects all the Tx queues having the COE supported.

-Serge(y)

> 
> >
> >-Serge(y)
> >
> >> -- 
> >> pw-bot: cr
> 
> BR,
> Rohan