netdev - Re: [PATCH v7 net-next 2/2] net: airoha: Introduce ethernet support for EN7581 SoC

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Message-ID: <ZpFGAqM9p-1mGLhM@lore-desk>
Date: Fri, 12 Jul 2024 17:04:34 +0200
From: Lorenzo Bianconi <lorenzo@...nel.org>
To: Jakub Kicinski <kuba@...nel.org>
Cc: netdev@...r.kernel.org, nbd@....name, lorenzo.bianconi83@...il.com,
	davem@...emloft.net, edumazet@...gle.com, pabeni@...hat.com,
	conor@...nel.org, linux-arm-kernel@...ts.infradead.org,
	robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
	conor+dt@...nel.org, devicetree@...r.kernel.org,
	catalin.marinas@....com, will@...nel.org, upstream@...oha.com,
	angelogioacchino.delregno@...labora.com,
	benjamin.larsson@...exis.eu, rkannoth@...vell.com,
	sgoutham@...vell.com, andrew@...n.ch, arnd@...db.de,
	horms@...nel.org
Subject: Re: [PATCH v7 net-next 2/2] net: airoha: Introduce ethernet support
 for EN7581 SoC

> On Fri, 12 Jul 2024 16:43:58 +0200 Lorenzo Bianconi wrote:
> > > On Fri, 12 Jul 2024 15:47:38 +0200 Lorenzo Bianconi wrote:  
> > > > The Airoha eth SoC architecture is similar to mtk_eth_soc one (e.g MT7988a).
> > > > The FrameEngine (FE) module has multiple GDM ports that are connected to
> > > > different blocks. Current airoha_eth driver supports just GDM1 that is connected
> > > > to a MT7530 DSA switch (I have not posted a tiny patch for mt7530 driver yet).
> > > > In the future we will support even GDM{2,3,4} that will connect to differ
> > > > phy modues (e.g. 2.5Gbps phy).  
> > > 
> > > What I'm confused by is the mentioned of DSA. You put the port in the
> > > descriptor, and there can only be one switch on the other side, right?  
> > 
> > do you mean fport in msg1 (airoha_dev_xmit())?
> > 
> > 	fport = port->id == 4 ? FE_PSE_PORT_GDM4 : port->id;
> > 	msg1 = FIELD_PREP(QDMA_ETH_TXMSG_FPORT_MASK, fport) |
> > 	       ...
> > 
> > fport refers to the GDM port and not to the dsa user port. Am I missing
> > something?
> 
> Ooh, I see, reading what you explained previously now makes sense.
> So only 1 of the ports goes to the DSA switch, and the other ones
> are connected to SoC pins? A diagram would be worth a 1000 words ;)

exactly, just GDM1 FE port is connected to the DSA switch.
I will try to do my best for the diagram :)

> 
> > > be in a setup like this :( It will have no way to figure out the real
> > > egress rate given that each netdev only sees a (non-)random sample
> > > of traffic sharing the queue :(  
> > 
> > do you prefer to remove BQL support?
> 
> No strong preference, I worry it will do more harm than good in
> this case. It's not what it's designed for basically. But without
> testing it's all speculation, so up to you, users can always disable
> using sysfs.

let me take a look to it again but, if it is not harmful, I would prefer
to remove it and add it in the future if necessary.

Regards,
Lorenzo

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