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Date: Fri, 24 Dec 2010 16:46:00 +0000
Message-ID: <AANLkTi=R58EGLrsT5sTk7JTqWvaeJ5caytHMt3VCSOki@mail.gmail.com>
Subject: Re: [PATCH RFC] mac80211: Extend channel to frequency mapping for 802.11j
From: Dave Kilroy <kilroyd@googlemail.com>
To: Bruno Randolf <br1@einfach.org>
Cc: johannes@sipsolutions.net, linville@tuxdriver.com,
	linux-wireless@vger.kernel.org
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On Fri, Dec 24, 2010 at 7:44 AM, Bruno Randolf <br1@einfach.org> wrote:
> Extend channel to frequency mapping for 802.11j Japan 4.9GHz band, according to
> IEEE802.11 section 17.3.8.3.2 and Annex J. Because there are now overlapping
> channel numbers in the 2GHz and 5GHz band we can't map from channel to
> frequency without knowing the band. This is no problem as in most contexts we
> know the band. In places where we don't know the band (and WEXT compatibility)
> we assume the 2GHz band for channels below 14.
>
> Signed-off-by: Bruno Randolf <br1@einfach.org>
> ---
> -int ieee80211_channel_to_frequency(int chan)
> +int ieee80211_channel_to_frequency(int chan, enum ieee80211_band band)
> ?{
> - ? ? ? if (chan < 14)
> - ? ? ? ? ? ? ? return 2407 + chan * 5;
> -
> - ? ? ? if (chan == 14)
> - ? ? ? ? ? ? ? return 2484;
> -
> - ? ? ? /* FIXME: 802.11j 17.3.8.3.2 */
> - ? ? ? return (chan + 1000) * 5;
> + ? ? ? /* see 802.11 17.3.8.3.2 and Annex J
> + ? ? ? ?* there are overlapping channel numbers in 5GHz and 2GHz bands */
> + ? ? ? if (band == IEEE80211_BAND_5GHZ) {
> + ? ? ? ? ? ? ? if (chan >= 182 && chan <= 196)
> + ? ? ? ? ? ? ? ? ? ? ? return 4000 + chan * 5;
> + ? ? ? ? ? ? ? else
> + ? ? ? ? ? ? ? ? ? ? ? return 5000 + chan * 5;
> + ? ? ? } else { /* IEEE80211_BAND_2GHZ */
> + ? ? ? ? ? ? ? if (chan == 14)
> + ? ? ? ? ? ? ? ? ? ? ? return 2484;
> + ? ? ? ? ? ? ? else if (chan < 14)
> + ? ? ? ? ? ? ? ? ? ? ? return 2407 + chan * 5;
> + ? ? ? ? ? ? ? else
> + ? ? ? ? ? ? ? ? ? ? ? return 0; /* not supported */
> + ? ? ? }
> ?}
> ?EXPORT_SYMBOL(ieee80211_channel_to_frequency);
>
> ?int ieee80211_frequency_to_channel(int freq)
> ?{
> + ? ? ? /* see 802.11 17.3.8.3.2 and Annex J */
> ? ? ? ?if (freq == 2484)
> ? ? ? ? ? ? ? ?return 14;
> -
> - ? ? ? if (freq < 2484)
> + ? ? ? else if (freq < 2484)
> ? ? ? ? ? ? ? ?return (freq - 2407) / 5;
> -
> - ? ? ? /* FIXME: 802.11j 17.3.8.3.2 */
> - ? ? ? return freq/5 - 1000;
> + ? ? ? else if (freq >= 4910 && freq <= 4980)
> + ? ? ? ? ? ? ? return (freq - 4000) / 5;
> + ? ? ? else
> + ? ? ? ? ? ? ? return (freq - 5000) / 5;
> ?}
> ?EXPORT_SYMBOL(ieee80211_frequency_to_channel);

You don't have to use them, but there are a few channel/frequency
conversion routines in include/ieee80211.h which could be reused in
these functions.


Regards,

Dave.