[PATCH wireless-next 3/5] b43: N-PHY: fix rev3+ RSSI calibration

[Luca Casati]

Three bugs in b43_nphy_rev3_rssi_cal():

- On rev7+ the selected VCM was written using the loop counter (8 after
  the search loop) instead of vcm_final; the 3-bit field turned that
  into VCM 0 on every rev7+ PHY.
- The distance used I*I + Q*I instead of I*I + Q*Q (brcmsmac
  wlc_phy_rssi_cal_nphy_rev3()).
- Negative W1/W2 offsets were rounded as -(abs(x + 4) / 8) instead of
  -((abs(x) + 4) / 8).

Found and fixed with the help of an AI coding assistant (Claude Opus 5.5),
by comparing mmiotraces of b43 and wl on the same card.

Signed-off-by: Luca Casati <luk00casati at gmail.com>
---
 drivers/net/wireless/broadcom/b43/phy_n.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/net/wireless/broadcom/b43/phy_n.c b/drivers/net/wireless/broadcom/b43/phy_n.c
index cabf61870..44769dbb7 100644
--- a/drivers/net/wireless/broadcom/b43/phy_n.c
+++ b/drivers/net/wireless/broadcom/b43/phy_n.c
@@ -2167,7 +2167,7 @@ static void b43_nphy_rev3_rssi_cal(struct b43_wldev *dev)
 				continue;
 			for (vcm = 0; vcm < 8; vcm++) {
 				currd = results[vcm][i] * results[vcm][i] +
-					results[vcm][i + 1] * results[vcm][i];
+					results[vcm][i + 1] * results[vcm][i + 1];
 				if (currd < mind) {
 					mind = currd;
 					minvcm = vcm;
@@ -2179,12 +2179,16 @@ static void b43_nphy_rev3_rssi_cal(struct b43_wldev *dev)
 			results_min[i] = minpoll;
 		}
 
-		/* Select the best VCM */
+		/*
+		 * Select the best VCM. (This used to write the loop counter,
+		 * 8, which the 3-bit field turned into VCM 0 on every rev7+
+		 * PHY.)
+		 */
 		if (dev->phy.rev >= 7)
 			b43_radio_maskset(dev,
 					  core ? R2057_NB_MASTER_CORE1 :
 						 R2057_NB_MASTER_CORE0,
-					  ~R2057_VCM_MASK, vcm);
+					  ~R2057_VCM_MASK, vcm_final);
 		else
 			b43_radio_maskset(dev, r | B2056_RX_RSSI_MISC,
 					  0xE3, vcm_final << 2);
@@ -2219,7 +2223,7 @@ static void b43_nphy_rev3_rssi_cal(struct b43_wldev *dev)
 				if (j / 2 == core) {
 					offset[j] = 232 - poll_results[j];
 					if (offset[j] < 0)
-						offset[j] = -(abs(offset[j] + 4) / 8);
+						offset[j] = -((abs(offset[j]) + 4) / 8);
 					else
 						offset[j] = (offset[j] + 4) / 8;
 					b43_nphy_scale_offset_rssi(dev, 0,
-- 
2.43.0