Re: [PATCH] ath9k: Save spectral scan data in network byteorder

[Simon Wunderlich <simon.wunderlich@s2003.tu-chemnitz.de>]

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On Tue, Jan 15, 2013 at 01:02:43PM +0100, Sven Eckelmann wrote:
> The sample data received through the spectral scan can be either in big or
> little endian byteorder. This information isn't stored in the output file.
> Therefore it is not possible for the analyzer software to find the correct byte
> order.
> 
> It is relative common to get the data from a low end AP in big endian mode and
> transfer it to another computer in little endian mode to analyze it. Therefore,
> it would be better to store it in network (big endian) byte order.

I'd agree that changing the byteorder to the "general" network order format is
a good idea, although we will break compatibility again - which should hopefully
be no problem as the original patch is pretty new anyway.

I was pondering about performance loss when we run spectral on the same machine
(i.e. maybe adding two useless byteswaps per value). OTOH the byteswaps are pretty
cheap and we do some computations anyway, so the performance difference should be quite
small.

Therefore,

Acked-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>

(I've CCd some more people in the reply so they can scream if they don't like it. ;])

Thanks,
	Simon

> 
> Signed-off-by: Sven Eckelmann <sven@open-mesh.com>
> Cc: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
> ---
> A patch for FFT_eval was also sent to the author.
> 
>  drivers/net/wireless/ath/ath9k/recv.c |   10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/wireless/ath/ath9k/recv.c b/drivers/net/wireless/ath/ath9k/recv.c
> index d7c129b..2fac787 100644
> --- a/drivers/net/wireless/ath/ath9k/recv.c
> +++ b/drivers/net/wireless/ath/ath9k/recv.c
> @@ -1064,8 +1064,9 @@ static void ath_process_fft(struct ath_softc *sc, struct ieee80211_hdr *hdr,
>  
>  	fft_sample.tlv.type = ATH_FFT_SAMPLE_HT20;
>  	fft_sample.tlv.length = sizeof(fft_sample) - sizeof(fft_sample.tlv);
> +	fft_sample.tlv.length = __cpu_to_be16(fft_sample.tlv.length);
>  
> -	fft_sample.freq = ah->curchan->chan->center_freq;
> +	fft_sample.freq = __cpu_to_be16(ah->curchan->chan->center_freq);
>  	fft_sample.rssi = fix_rssi_inv_only(rs->rs_rssi_ctl0);
>  	fft_sample.noise = ah->noise;
>  
> @@ -1106,13 +1107,16 @@ static void ath_process_fft(struct ath_softc *sc, struct ieee80211_hdr *hdr,
>  	mag_info = ((struct ath_ht20_mag_info *)radar_info) - 1;
>  
>  	/* Apply exponent and grab further auxiliary information. */
> -	for (i = 0; i < SPECTRAL_HT20_NUM_BINS; i++)
> +	for (i = 0; i < SPECTRAL_HT20_NUM_BINS; i++) {
>  		fft_sample.data[i] = bins[i] << mag_info->max_exp;
> +		fft_sample.data[i] = __cpu_to_be16(fft_sample.data[i]);
> +	}
>  
>  	fft_sample.max_magnitude = spectral_max_magnitude(mag_info->all_bins);
> +	fft_sample.max_magnitude = __cpu_to_be16(fft_sample.max_magnitude);
>  	fft_sample.max_index = spectral_max_index(mag_info->all_bins);
>  	fft_sample.bitmap_weight = spectral_bitmap_weight(mag_info->all_bins);
> -	fft_sample.tsf = tsf;
> +	fft_sample.tsf = __cpu_to_be64(tsf);
>  
>  	ath_debug_send_fft_sample(sc, &fft_sample.tlv);
>  #endif
> -- 
> 1.7.10.4
> 
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