netdev - Re: [PATCH net-next v4 6/9] net: sparx5: verify RGMII speeds

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Message-ID: <20241216121040.2dpxb7mv6h3u3r42@DEN-DL-M70577>
Date: Mon, 16 Dec 2024 12:10:40 +0000
From: Daniel Machon <daniel.machon@...rochip.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
CC: <UNGLinuxDriver@...rochip.com>, Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, "Lars
 Povlsen" <lars.povlsen@...rochip.com>, Steen Hegelund
	<Steen.Hegelund@...rochip.com>, Horatiu Vultur
	<horatiu.vultur@...rochip.com>, <jacob.e.keller@...el.com>,
	<robh@...nel.org>, <krzk+dt@...nel.org>, <conor+dt@...nel.org>,
	<devicetree@...r.kernel.org>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
	<robert.marko@...tura.hr>
Subject: Re: [PATCH net-next v4 6/9] net: sparx5: verify RGMII speeds

> On Fri, Dec 13, 2024 at 02:41:05PM +0100, Daniel Machon wrote:
> > When doing a port config, we verify the port speed against the PHY mode
> > and supported speeds of that PHY mode. Add checks for the four RGMII phy
> > modes: RGMII, RGMII_ID, RGMII_TXID and RGMII_RXID.
> >
> > Reviewed-by: Steen Hegelund <Steen.Hegelund@...rochip.com>
> > Reviewed-by: Horatiu Vultur <horatiu.vultur@...rochip.com>
> > Signed-off-by: Daniel Machon <daniel.machon@...rochip.com>
> 
> You do realise that phylink knows what speeds each interface supports
> (see phylink_get_capabilities()) and restricts the media advertisement
> to ensure that ethtool link modes that can't be supported by the MAC
> capabilities and set of interfaces that would be used are not
> advertised.
> 
> This should mean none of your verification ever triggers. If it does,
> then I'd like to know about it.

Yes, I agree. Having an extra look at phylink, these checks should not trigger
at all.

As it is, the default switch case is to throw an error, so without this
addition, the sparx5_port_verify_speed() function will fail when the PHY mode
is any of RGMII{_ID,_TXID,_RXID}. This patch just follows the established
pattern of adding the new PHY mode and checking the speed. TBH, I think that
all the checks in this function can be removed entirely, but that is something
I would like to verify and follow up on in a separate series, if that is OK? 

Thanks.

/Daniel