netdev - Re: [PATCH net-next v5 2/5] ethtool: netlink: add ETHTOOL_MSG_MSE

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Message-ID: <aMjt9iVcNWYf0opD@pengutronix.de>
Date: Tue, 16 Sep 2025 06:56:22 +0200
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Andrew Lunn <andrew@...n.ch>, "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Donald Hunter <donald.hunter@...il.com>,
	Jonathan Corbet <corbet@....net>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>,
	Kory Maincent <kory.maincent@...tlin.com>,
	Maxime Chevallier <maxime.chevallier@...tlin.com>,
	Nishanth Menon <nm@...com>, kernel@...gutronix.de,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	UNGLinuxDriver@...rochip.com, linux-doc@...r.kernel.org,
	Michal Kubecek <mkubecek@...e.cz>, Roan van Dijk <roan@...tonic.nl>
Subject: Re: [PATCH net-next v5 2/5] ethtool: netlink: add
 ETHTOOL_MSG_MSE_GET and wire up PHY MSE access

On Mon, Sep 15, 2025 at 08:07:20AM -0700, Jakub Kicinski wrote:
> On Mon, 15 Sep 2025 11:30:52 +0200 Oleksij Rempel wrote:
> > On Fri, Sep 12, 2025 at 05:00:53PM -0700, Jakub Kicinski wrote:
> > > On Fri, 12 Sep 2025 12:07:42 +0200 Oleksij Rempel wrote:  
> > > > I would prefer to keep u64 for refresh-rate-ps and num-symbols.
> > > > 
> > > > My reasoning comes from comparing the design decisions of today's industrial
> > > > hardware to the projected needs of upcoming standards like 800 Gbit/s. This
> > > > analysis shows that future PHYs will require values that exceed the limits of a
> > > > u32.  
> > > 
> > > but u64 may or may not also have some alignment expectations, which uint
> > > explicitly excludes  
> > 
> > just to confirm - if we declare an attribute as type: uint in the YAML
> > spec, the kernel side can still use nla_put_u64() to send a 64-bit
> > value, correct? My understanding is that uint is a flexible integer
> > type, so userspace decoders will accept both 4-byte and 8-byte encodings
> > transparently.
> 
> Theoretically, and yes. But why would you use put_u64 and not
> put_uint() ?

rater.. rater.. rater.. (sound of rusty gears slowly moving)

Right, I was thinking of uint as u32. But in NLA, NLA_UINT is handled
like NLA_U64, so the max is U64_MAX. That clears it up, thanks!

Best Regards,
Oleksij
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