[PATCH wireless-next 4/5] b43: N-PHY: wait for the first 2057 RC calibration run

[Luca Casati]

RCCAL_DONE_OSCCAP still shows the previous run's done bit for a few us
after a start, and the first (SCAP) run polled it immediately, so the
run was stopped before it happened. RCCAL_SCAP_VAL then read 0 (wl
gets 8 on a BCM43228), which detunes the TX low-pass filter set up in
the rev7+ workarounds. Sleep before polling, as the other two runs do.

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 | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/broadcom/b43/phy_n.c b/drivers/net/wireless/broadcom/b43/phy_n.c
index 44769dbb7..cd50614ff 100644
--- a/drivers/net/wireless/broadcom/b43/phy_n.c
+++ b/drivers/net/wireless/broadcom/b43/phy_n.c
@@ -938,8 +938,15 @@ static u16 b43_radio_2057_rccal(struct b43_wldev *dev)
 	}
 	b43_radio_write(dev, R2057_RCCAL_X1, 0x6E);
 
-	/* Start, wait, stop */
+	/*
+	 * Start, wait, stop. DONE still holds the previous run's done bit
+	 * for a few us after the start, so give the cal time to clear it
+	 * before polling, as for the other two runs. Polling right away
+	 * stopped this (SCAP) cal before it ran and left RCCAL_SCAP_VAL at
+	 * 0, which detunes the TX LPF on radio rev 9.
+	 */
 	b43_radio_write(dev, R2057_RCCAL_START_R1_Q1_P1, 0x55);
+	usleep_range(70, 140);
 	if (!b43_radio_wait_value(dev, R2057_RCCAL_DONE_OSCCAP, 2, 2, 500,
 				  5000000))
 		b43dbg(dev->wl, "Radio 0x2057 rccal timeout\n");
-- 
2.43.0