netdev - Re: [PATCH v4 net-next 10/15] net: dsa: Validate hardware support for MST

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Date:   Wed, 16 Mar 2022 15:03:49 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Tobias Waldekranz <tobias@...dekranz.com>
Cc:     davem@...emloft.net, kuba@...nel.org, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Ivan Vecera <ivecera@...hat.com>,
        Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <razor@...ckwall.org>,
        Russell King <linux@...linux.org.uk>,
        Petr Machata <petrm@...dia.com>,
        Ido Schimmel <idosch@...dia.com>,
        Matt Johnston <matt@...econstruct.com.au>,
        Cooper Lees <me@...perlees.com>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, bridge@...ts.linux-foundation.org
Subject: Re: [PATCH v4 net-next 10/15] net: dsa: Validate hardware support
 for MST

On Wed, Mar 16, 2022 at 10:15:18AM +0100, Tobias Waldekranz wrote:
> >> +int dsa_port_mst_enable(struct dsa_port *dp, bool on,
> >> +			struct netlink_ext_ack *extack)
> >> +{
> >> +	if (!on)
> >> +		return 0;
> >> +
> >> +	if (!dsa_port_supports_mst(dp)) {
> >> +		NL_SET_ERR_MSG_MOD(extack, "Hardware does not support MST");
> >> +		return -EINVAL;
> >> +	}
> >> +
> >> +	return 0;
> >> +}
> >
> > Experimenting a bit... maybe this looks tidier? We make the "if" condition
> > have the same basic structure as the previous "if (br_mst_enabled(br) &&
> > !dsa_port_supports_mst(dp))", albeit transformed using De Morgan's rules.
> >
> > {
> > 	if (!on || dsa_port_supports_mst(dp))
> > 		return 0;
> >
> > 	NL_SET_ERR_MSG_MOD(extack, "Hardware does not support MST");
> > 	return -EINVAL;
> > }
> 
> I initially had it like this. It looks tidier, yes - but to me the
> intent is less obvious when reading it. How about:
> 
> {
> 	if (on && !dsa_port_supports_mst(dp)) {
> 		NL_SET_ERR_MSG_MOD(extack, "Hardware does not support MST");
> 		return -EINVAL;
> 	}
> 
> 	return 0;
> }

Yes, let's go with this.