b43: Fix noise calculation WARN_ON

This removes a WARN_ON that is responsible for the following koops:
http://www.kerneloops.org/searchweek.php?search=b43_generate_noise_sample

The comment in the patch describes why it's safe to simply remove
the check.

Signed-off-by: Michael Buesch <mb@bu3sch.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

2 files changed, 10 insertions, 7 deletions

diff --git a/drivers/net/wireless/b43/b43.h b/drivers/net/wireless/b43/b43.h
index dfa4bdd5597c..d3db298c05fc 100644
--- a/drivers/net/wireless/b43/b43.h
+++ b/drivers/net/wireless/b43/b43.h
@@ -630,7 +630,6 @@ struct b43_pio {
 
 /* Context information for a noise calculation (Link Quality). */
 struct b43_noise_calculation {
-        u8 channel_at_start;
         bool calculation_running;
         u8 nr_samples;
         s8 samples[8][4];
diff --git a/drivers/net/wireless/b43/main.c b/drivers/net/wireless/b43/main.c
index 6c3d9ea0a9f8..fa4b0d8b74a2 100644
--- a/drivers/net/wireless/b43/main.c
+++ b/drivers/net/wireless/b43/main.c
@@ -1145,7 +1145,6 @@ static void b43_generate_noise_sample(struct b43_wldev *dev)
         b43_jssi_write(dev, 0x7F7F7F7F);
         b43_write32(dev, B43_MMIO_MACCMD,
                     b43_read32(dev, B43_MMIO_MACCMD) | B43_MACCMD_BGNOISE);
-        B43_WARN_ON(dev->noisecalc.channel_at_start != dev->phy.channel);
 }
 
 static void b43_calculate_link_quality(struct b43_wldev *dev)
@@ -1154,7 +1153,6 @@ static void b43_calculate_link_quality(struct b43_wldev *dev)
 
         if (dev->noisecalc.calculation_running)
                 return;
-        dev->noisecalc.channel_at_start = dev->phy.channel;
         dev->noisecalc.calculation_running = 1;
         dev->noisecalc.nr_samples = 0;
 
@@ -1171,9 +1169,16 @@ static void handle_irq_noise(struct b43_wldev *dev)
 
         /* Bottom half of Link Quality calculation. */
 
+        /* Possible race condition: It might be possible that the user
+         * changed to a different channel in the meantime since we
+         * started the calculation. We ignore that fact, since it's
+         * not really that much of a problem. The background noise is
+         * an estimation only anyway. Slightly wrong results will get damped
+         * by the averaging of the 8 sample rounds. Additionally the
+         * value is shortlived. So it will be replaced by the next noise
+         * calculation round soon. */
+
         B43_WARN_ON(!dev->noisecalc.calculation_running);
-        if (dev->noisecalc.channel_at_start != phy->channel)
-                goto drop_calculation;
         *((__le32 *)noise) = cpu_to_le32(b43_jssi_read(dev));
         if (noise[0] == 0x7F || noise[1] == 0x7F ||
             noise[2] == 0x7F || noise[3] == 0x7F)
@@ -1214,11 +1219,10 @@ static void handle_irq_noise(struct b43_wldev *dev)
                         average -= 48;
 
                 dev->stats.link_noise = average;
-              drop_calculation:
                 dev->noisecalc.calculation_running = 0;
                 return;
         }
-      generate_new:
+generate_new:
         b43_generate_noise_sample(dev);
 }