netdev - Re: [PATCH net-next 6/8] net: dsa: ocelot: use ds->num_tx_queues = OCELOT_NUM

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Date: Sun, 2 Jun 2024 21:02:18 -0500
From: Colin Foster <colin.foster@...advantage.com>
To: Vladimir Oltean <vladimir.oltean@....com>
Cc: netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Claudiu Manoil <claudiu.manoil@....com>,
	Alexandre Belloni <alexandre.belloni@...tlin.com>,
	UNGLinuxDriver@...rochip.com, Andrew Lunn <andrew@...n.ch>,
	Florian Fainelli <f.fainelli@...il.com>,
	Russell King <linux@...linux.org.uk>
Subject: Re: [PATCH net-next 6/8] net: dsa: ocelot: use ds->num_tx_queues =
 OCELOT_NUM_TC for all models

On Thu, May 30, 2024 at 07:33:31PM +0300, Vladimir Oltean wrote:
> Russell King points out that seville_vsc9953 populates
> felix->info->num_tx_queues = 8, but this doesn't make it all the way
> into ds->num_tx_queues (which is how the user interface netdev queues
> get allocated) [1].
> 
> [1]: https://lore.kernel.org/all/20240415160150.yejcazpjqvn7vhxu@skbuf/
> 
> When num_tx_queues=0 for seville, this is implicitly converted to 1 by
> dsa_user_create(), and this is good enough for basic operation for a
> switch port. The tc qdisc offload layer works with netdev TX queues,
> so for QoS offload we need to pretend we have multiple TX queues. The
> VSC9953, like ocelot_ext, doesn't export QoS offload, so it doesn't
> really matter. But we can definitely set num_tx_queues=8 for all
> switches.
> 
> The felix->info->num_tx_queues construct itself seems unnecessary.
> It was introduced by commit de143c0e274b ("net: dsa: felix: Configure
> Time-Aware Scheduler via taprio offload") at a time when vsc9959
> (LS1028A) was the only switch supported by the driver.
> 
> 8 traffic classes, and 1 queue per traffic class, is a common
> architectural feature of all switches in the family. So they could
> all just set OCELOT_NUM_TC and be fine.
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> ---
>  drivers/net/dsa/ocelot/felix.h           | 1 -
>  drivers/net/dsa/ocelot/felix_vsc9959.c   | 4 ++--
>  drivers/net/dsa/ocelot/ocelot_ext.c      | 3 +--

Tested-by: Colin Foster <colin.foster@...advantage.com>