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Message-ID: <b3184a3baff2e1ab031e3dcc426df9a2234b89d5.camel@sipsolutions.net>
Subject: Re: question about struct ieee80211_iface_combination
From:   Johannes Berg <johannes@sipsolutions.net>
To:     Arend van Spriel <arend.vanspriel@broadcom.com>
Cc:     linux-wireless <linux-wireless@vger.kernel.org>
Date:   Tue, 25 Apr 2023 20:14:31 +0200
In-Reply-To: <9de1cb94-7b60-3d1d-3833-1b08624af645@broadcom.com>
References: <9de1cb94-7b60-3d1d-3833-1b08624af645@broadcom.com>
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Hi Arend,

On Tue, 2023-04-25 at 12:01 +0200, Arend van Spriel wrote:
> My brain is tripping over a field in struct ieee80211_iface_combination,=
=20
> ie. the num_different_channels. Looking at the name I tend to think that=
=20
> num_different_channel =3D 0 means the interfaces must all operate on the=
=20
> same channel. However, in most places it is configured as 1 or more. The=
=20
> documentation in cfg80211.h [1] is not unambiguous about it in my=20
> opinion. By now it probably depends on how user-space uses it.

Well it's not valid for it to be 0 in the first place:

static int wiphy_verify_combinations(struct wiphy *wiphy)
{
...
        for (i =3D 0; i < wiphy->n_iface_combinations; i++) {
...
        for (i =3D 0; i < wiphy->n_iface_combinations; i++) {
...
                /* Need at least one channel */
                if (WARN_ON(!c->num_different_channels))
                        return -EINVAL;


So really what was meant that _1_ means you only have a single channel,
and so on. Are you tripping over the "different"? The way I read it, is
that with all the interfaces you have, you can have N different
channels, i.e. looking at it "globally". It seems maybe you're more
interpreting it as "additionally" to the first interface?

johannes