mac80211: use hardware flags for signal/noise units

trying to clean up the signal/noise code. the previous code in mac80211 had
confusing names for the related variables, did not have much definition of
what units of signal and noise were provided and used implicit mechanisms from
the wireless extensions.

this patch introduces hardware capability flags to let the hardware specify
clearly if it can provide signal and noise level values and which units it can
provide. this also anticipates possible new units like RCPI in the future.

for signal:

  IEEE80211_HW_SIGNAL_UNSPEC - unspecified, unknown, hw specific
  IEEE80211_HW_SIGNAL_DB     - dB difference to unspecified reference point
  IEEE80211_HW_SIGNAL_DBM    - dBm, difference to 1mW

for noise we currently only have dBm:

  IEEE80211_HW_NOISE_DBM     - dBm, difference to 1mW

if IEEE80211_HW_SIGNAL_UNSPEC or IEEE80211_HW_SIGNAL_DB is used the driver has
to provide the maximum value (max_signal) it reports in order for applications
to make sense of the signal values.

i tried my best to find out for each driver what it can provide and update it
but i'm not sure (?) for some of them and used the more conservative guess in
doubt. this can be fixed easily after this patch has been merged by changing
the hardware flags of the driver.

DRIVER          SIGNAL    MAX	NOISE   QUAL
-----------------------------------------------------------------
adm8211         unspec(?) 100   n/a     missing
at76_usb        unspec(?) (?)   unused  missing
ath5k           dBm             dBm     percent rssi
b43legacy       dBm             dBm     percent jssi(?)
b43             dBm             dBm     percent jssi(?)
iwl-3945        dBm             dBm     percent snr+more
iwl-4965        dBm             dBm     percent snr+more
p54             unspec    127   n/a     missing
rt2x00          dBm	        n/a     percent rssi+tx/rx frame success
  rt2400        dBm             n/a
  rt2500pci     dBm             n/a
  rt2500usb     dBm             n/a
  rt61pci       dBm             n/a
  rt73usb       dBm             n/a
rtl8180         unspec(?) 65    n/a     (?)
rtl8187         unspec(?) 65    (?)     noise(?)
zd1211          dB(?)     100   n/a     percent

drivers/net/wireless/ath5k/base.c:      Changes-licensed-under: 3-Clause-BSD

Signed-off-by: Bruno Randolf <br1@einfach.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 34 insertions, 13 deletions

diff --git a/include/net/mac80211.h b/include/net/mac80211.h
index 75a34609eed7..909956c97c44 100644
--- a/include/net/mac80211.h
+++ b/include/net/mac80211.h
@@ -336,13 +336,16 @@ enum mac80211_rx_flags {
  * The low-level driver should provide this information (the subset
  * supported by hardware) to the 802.11 code with each received
  * frame.
+ *
  * @mactime: value in microseconds of the 64-bit Time Synchronization Function
  *      (TSF) timer when the first data symbol (MPDU) arrived at the hardware.
  * @band: the active band when this frame was received
  * @freq: frequency the radio was tuned to when receiving this frame, in MHz
- * @ssi: signal strength when receiving this frame
- * @signal: used as 'qual' in statistics reporting
- * @noise: PHY noise when receiving this frame
+ * @signal: signal strength when receiving this frame, either in dBm, in dB or
+ *      unspecified depending on the hardware capabilities flags
+ *      @IEEE80211_HW_SIGNAL_*
+ * @noise: noise when receiving this frame, in dBm.
+ * @qual: overall signal quality indication, in percent (0-100).
  * @antenna: antenna used
  * @rate_idx: index of data rate into band's supported rates
  * @flag: %RX_FLAG_*
@@ -351,9 +354,9 @@ struct ieee80211_rx_status {
         u64 mactime;
         enum ieee80211_band band;
         int freq;
-        int ssi;
         int signal;
         int noise;
+        int qual;
         int antenna;
         int rate_idx;
         int flag;
@@ -392,7 +395,8 @@ enum ieee80211_tx_status_flags {
  *      relevant only if IEEE80211_TX_STATUS_AMPDU was set.
  * @ampdu_ack_map: block ack bit map for the aggregation.
  *      relevant only if IEEE80211_TX_STATUS_AMPDU was set.
- * @ack_signal: signal strength of the ACK frame
+ * @ack_signal: signal strength of the ACK frame either in dBm, dB or unspec
+ *      depending on hardware capabilites flags @IEEE80211_HW_SIGNAL_*
  */
 struct ieee80211_tx_status {
         struct ieee80211_tx_control control;
@@ -703,6 +707,25 @@ enum ieee80211_tkip_key_type {
  * @IEEE80211_HW_2GHZ_SHORT_PREAMBLE_INCAPABLE:
  *      Hardware is not capable of receiving frames with short preamble on
  *      the 2.4 GHz band.
+ *
+ * @IEEE80211_HW_SIGNAL_UNSPEC:
+ *      Hardware can provide signal values but we don't know its units. We
+ *      expect values between 0 and @max_signal.
+ *      If possible please provide dB or dBm instead.
+ *
+ * @IEEE80211_HW_SIGNAL_DB:
+ *      Hardware gives signal values in dB, decibel difference from an
+ *      arbitrary, fixed reference. We expect values between 0 and @max_signal.
+ *      If possible please provide dBm instead.
+ *
+ * @IEEE80211_HW_SIGNAL_DBM:
+ *      Hardware gives signal values in dBm, decibel difference from
+ *      one milliwatt. This is the preferred method since it is standardized
+ *      between different devices. @max_signal does not need to be set.
+ *
+ * @IEEE80211_HW_NOISE_DBM:
+ *      Hardware can provide noise (radio interference) values in units dBm,
+ *      decibel difference from one milliwatt.
  */
 enum ieee80211_hw_flags {
         IEEE80211_HW_HOST_GEN_BEACON_TEMPLATE           = 1<<0,
@@ -710,6 +733,10 @@ enum ieee80211_hw_flags {
         IEEE80211_HW_HOST_BROADCAST_PS_BUFFERING        = 1<<2,
         IEEE80211_HW_2GHZ_SHORT_SLOT_INCAPABLE          = 1<<3,
         IEEE80211_HW_2GHZ_SHORT_PREAMBLE_INCAPABLE      = 1<<4,
+        IEEE80211_HW_SIGNAL_UNSPEC                      = 1<<5,
+        IEEE80211_HW_SIGNAL_DB                          = 1<<6,
+        IEEE80211_HW_SIGNAL_DBM                         = 1<<7,
+        IEEE80211_HW_NOISE_DBM                          = 1<<8,
 };
 
 /**
@@ -740,12 +767,8 @@ enum ieee80211_hw_flags {
  *
  * @channel_change_time: time (in microseconds) it takes to change channels.
  *
- * @max_rssi: Maximum value for ssi in RX information, use
- *      negative numbers for dBm and 0 to indicate no support.
- *
- * @max_signal: like @max_rssi, but for the signal value.
- *
- * @max_noise: like @max_rssi, but for the noise value.
+ * @max_signal: Maximum value for signal (rssi) in RX information, used
+ *     only when @IEEE80211_HW_SIGNAL_UNSPEC or @IEEE80211_HW_SIGNAL_DB
  *
  * @queues: number of available hardware transmit queues for
  *      data packets. WMM/QoS requires at least four, these
@@ -775,9 +798,7 @@ struct ieee80211_hw {
         int channel_change_time;
         int vif_data_size;
         u16 queues, ampdu_queues;
-        s8 max_rssi;
         s8 max_signal;
-        s8 max_noise;
 };
 
 /**