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From:   Arend Van Spriel <arend.vanspriel@broadcom.com>
To:     Johannes Berg <johannes@sipsolutions.net>
CC:     "linux-wireless" <linux-wireless@vger.kernel.org>
Date:   Tue, 25 Apr 2023 21:52:14 +0200
Message-ID: <187b9f945b0.279b.9b12b7fc0a3841636cfb5e919b41b954@broadcom.com>
In-Reply-To: <b3184a3baff2e1ab031e3dcc426df9a2234b89d5.camel@sipsolutions.net>
References: <9de1cb94-7b60-3d1d-3833-1b08624af645@broadcom.com>
 <b3184a3baff2e1ab031e3dcc426df9a2234b89d5.camel@sipsolutions.net>
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Subject: Re: question about struct ieee80211_iface_combination
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On April 25, 2023 8:14:33 PM Johannes Berg <johannes@sipsolutions.net> wrote:

> 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,
>> ie. the num_different_channels. Looking at the name I tend to think that
>> num_different_channel = 0 means the interfaces must all operate on the
>> same channel. However, in most places it is configured as 1 or more. The
>> documentation in cfg80211.h [1] is not unambiguous about it in my
>> 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 = 0; i < wiphy->n_iface_combinations; i++) {
> ...
>        for (i = 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

Yup. That WARN_ON is a big help ;-)

> 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?

Thanks for taking time to clarify this to me.

Regards,
Arend


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