Re: [PATCH v3 1/9] cfg80211: Add helper function to identify 6GHz PSC channel

[Johannes Berg <johannes@xxxxxxxxxxxxxxxx>]

On Tue, 2020-05-26 at 15:42 -0700, Pradeep Kumar Chitrapu wrote:
Hi,

Just checked what we had here, and it was the following:

> +/**
> + * ieee80211_is_channel_psc - is 6ghz channel a Preferred Scanning Channel (PSC)
> + *
> + * @chan: struct ieee80211_channel to determine
> + * Return: True if 6ghz channel is a PSC channel. False for the rest.
> + */
> +static inline bool ieee80211_is_channel_psc(struct ieee80211_channel *chan)
> +{
> +	if (chan->band != NL80211_BAND_6GHZ)
> +		return false;
> +
> +	/*
> +	 * From IEEE P802.11ax/D6.1: The set of 20 MHz channels in the 6 GHz
> +	 * band, with channel center frequency, ch_a = Channel starting
> +	 * frequency – 55  80 × n (MHz) are referred to as preferred scanning
> +	 * channels (PSCs). Channel starting frequency is defined in 27.3.23.2
> +	 * (Channel allocation in the 6 GHz band), and n = 1, …, 15.
> +	 */
> +	if (!(((chan->center_freq - 5950 + 55) >> 4) % 5))
> +		return true;
> +
> +	return false;
> +}


static inline bool cfg80211_is_psc(struct ieee80211_channel *chan)
{
        int chan_num =
                ieee80211_frequency_to_channel(chan->center_freq);

        return chan->band == NL80211_BAND_6GHZ && chan_num % 16 == 5;
}

Apart from the naming, where I guess I prefer actually

	cfg80211_channel_is_psc()

or so, does that seem reasonable to you? I'd prefer not to hardcode
frequencies everywhere, so in that regard I like our version better.
Maybe bail out earlier if band != 6 ghz:

static inline bool cfg80211_channel_is_psc(struct ieee80211_channel *chan)
{
	if (chan->band != NL80211_BAND_6GHZ)
		return false;

	return ieee80211_frequency_to_channel(chan->center_freq) % 16 == 5;
}

johannes