netdev - Re: DSA using cpsw and lan9303

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Message-ID: <yw1x5ype3n6r.fsf@mansr.com>
Date:   Wed, 16 Feb 2022 14:23:24 +0000
From:   Måns Rullgård <mans@...sr.com>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>, netdev@...r.kernel.org,
        Egil Hjelmeland <privat@...l-hjelmeland.no>,
        Andrew Lunn <andrew@...n.ch>,
        Juergen Borleis <jbe@...gutronix.de>,
        Grygorii Strashko <grygorii.strashko@...com>,
        lorenzo@...nel.org
Subject: Re: DSA using cpsw and lan9303

Vladimir Oltean <olteanv@...il.com> writes:

> On Wed, Feb 16, 2022 at 01:17:47PM +0000, Måns Rullgård wrote:
>> > Some complaints about accessing the CPU port as dsa_to_port(chip->ds, 0),
>> > but it's not the first place in this driver where that is done.
>> 
>> What would be the proper way to do it?
>
> Generally speaking:
>
> 	struct dsa_port *cpu_dp;
>
> 	dsa_switch_for_each_cpu_port(cpu_dp, ds)
> 		break;
>
> 	// use cpu_dp
>
> If your code runs after dsa_tree_setup_default_cpu(), which contains the
> "DSA: tree %d has no CPU port\n" check, you don't even need to check
> whether cpu_dp was found or not - it surely was. Everything that runs
> after dsa_register_switch() has completed successfully - for example the
> DSA ->setup() method - qualifies here.

In this particular driver, the setup function contains this:

	/* Make sure that port 0 is the cpu port */
	if (!dsa_is_cpu_port(ds, 0)) {
		dev_err(chip->dev, "port 0 is not the CPU port\n");
		return -EINVAL;
	}

I take this to mean that port 0 is guaranteed to be the cpu port.  Of
course, it can't hurt to be thorough just in case that check is ever
removed.

-- 
Måns Rullgård