On Sun, Dec 20, 2009 at 10:42 PM, Luis R. Rodriguez <mcgrof@xxxxxxxxx> wrote:
> On Sun, Dec 20, 2009 at 5:10 AM, Valentin Manea <linux-wireless@xxxxxx> wrote:
>> Hi,
>>
>> I'm running compat-wireless-2.6.33-rc1 and iw list shows some confusing HT
>> capabilities:
>> Band 1:
>> HT capabilities: 0x082c
>> * 20 MHz operation
>> * SM PS disabled
>> * 20 MHz short GI
>> * max A-MSDU len 7935
>>
>> but for 802.11a channels:
>> Band 2:
>> HT capabilities: 0x086e
>> * 20/40 MHz operation
>> * SM PS disabled
>> * 20 MHz short GI
>> * 40 MHz short GI
>> * max A-MSDU len 7935
>>
>> While I can't tell when this happened, I remember older 2.6.29 releases
>> supported HT40 for both bands.
>
> How do you know? What makes you believe that was the case?
>
>> The wireless card is an Intel 4965 on a Thinkpad T61.
>
> The ht_cap that gets parsed and sent back through nl80211 is
> initialized in iwl-agn on iwl-core.c on iwlcore_init_ht_hw_capab() as
> follows
>
> static void iwlcore_init_ht_hw_capab(const struct iwl_priv *priv,
> struct ieee80211_sta_ht_cap *ht_info,
> enum ieee80211_band band)
> {
> ....
> if (priv->hw_params.ht40_channel & BIT(band)) {
> ht_info->cap |= IEEE80211_HT_CAP_SUP_WIDTH_20_40;
> ht_info->cap |= IEEE80211_HT_CAP_SGI_40;
> ht_info->mcs.rx_mask[4] = 0x01;
> max_bit_rate = MAX_BIT_RATE_40_MHZ;
> }
> ....
> }
>
> And the priv->hw_params.ht40_channel gets initialized for 4965
> hardware on iwl4965_hw_set_hw_params():
>
> static int iwl4965_hw_set_hw_params(struct iwl_priv *priv)
> {
> ...
> priv->hw_params.ht40_channel = BIT(IEEE80211_BAND_5GHZ);
> ....
> }
>
> iwl-5000 and iwl-6000 sets this to both bands:
>
> int iwl5000_hw_set_hw_params(struct iwl_priv *priv)
> {
> ....
> priv->hw_params.ht40_channel = BIT(IEEE80211_BAND_2GHZ) |
> BIT(IEEE80211_BAND_5GHZ);
> ....
> }
>
> static int iwl6000_hw_set_hw_params(struct iwl_priv *priv)
> {
> ....
> priv->hw_params.ht40_channel = BIT(IEEE80211_BAND_2GHZ) |
> BIT(IEEE80211_BAND_5GHZ);
> ....
> }
>
> So it appears to be done explicitly in software, not sure if hardware
> does support HT40 on 2.4 GHz band on the 4965, Intel folks would
> though.
>
AFAIK the Windows driver supports 2GHz HT40 for all cards, but
disables it by default, even for IWL5/6xxx.
> Luis
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