netdev - Re: [RFC PATCH net-next 3/4] net: systemport: use standard netdevice notifier to detect DSA presence

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Date:   Mon, 21 Dec 2020 23:06:19 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Florian Fainelli <f.fainelli@...il.com>
CC:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        "bcm-kernel-feedback-list@...adcom.com" 
        <bcm-kernel-feedback-list@...adcom.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [RFC PATCH net-next 3/4] net: systemport: use standard netdevice
 notifier to detect DSA presence

On Mon, Dec 21, 2020 at 02:33:16PM -0800, Florian Fainelli wrote:
> On 12/20/2020 8:53 PM, Florian Fainelli wrote:
> > The call to netif_set_real_num_tx_queues() succeeds and
> > slave_dev->real_num_tx_queues is changed to 4 accordingly. The loop that
> > assigns the internal queue mapping (priv->ring_map) is correctly limited
> > to 4, however we get two calls per switch port instead of one. I did not
> > have much time to debug why we get called twice but I will be looking
> > into this tomorrow.
>
> There was not any bug other than there are two instances of a SYSTEMPORT
> device in my system and they both receive the same notification.
>
> So we do need to qualify which of the notifier block matches the device
> of interest, because if we do extract the private structure from the
> device being notified, it is always going to match.
>
> Incremental fixup here:
>
> https://github.com/ffainelli/linux/commit/0eea16e706a73c56a36d701df483ff73211aae7f

...duh.
And when you come to think that I had deleted that code in my patch, not
understanding what it's for... Coincidentally this is also the reason
why I got the prints twice. Sorry :(

>
> and you can add Tested-by: Florian Fainelli <f.fainelli@...il.com> when
> you resubmit.
>
> Thanks, this is a really nice cleanup.

Thanks.

Do you think we need some getters for dp->index and dp->ds->index, to preserve
some sort of data structure encapsulation from the outside world (although it's
not as if the members of struct dsa_switch and struct dsa_port still couldn't
be accessed directly)?

But then, there's the other aspect. We would have some shiny accessors for DSA
properties, but we're resetting the net_device's number of TX queues.
So much for data encapsulation.