On USB a register read is a WMI round trip and a timeout returns -1.
The spectral trigger reads AR_RX_FILTER back, ORs in the PHY error
bits and writes it, so a timed-out read stores 0xffffffff and the
device forwards every frame and PHY error to the host.

Add ath9k_hw_enable_rxfilter(), which sets the requested bits with
REG_SET_BIT() instead of reading the register from the driver, and
use it in the trigger. With firmware 1.4 and later the
read-modify-write is done by the firmware; older firmware still reads
from the host.

Fixes: e93d083f42a1 ("ath9k: add spectral scan feature")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Nerijus Bendžiūnas <nerijus.bendziunas@gmail.com>
---
 .../net/wireless/ath/ath9k/common-spectral.c  |  7 ++----
 drivers/net/wireless/ath/ath9k/hw.c           | 23 +++++++++++++++++++
 drivers/net/wireless/ath/ath9k/hw.h           |  1 +
 3 files changed, 26 insertions(+), 5 deletions(-)

diff --git a/drivers/net/wireless/ath/ath9k/common-spectral.c b/drivers/net/wireless/ath/ath9k/common-spectral.c
index ca01a07f6630..73c1eb4ebe0e 100644
--- a/drivers/net/wireless/ath/ath9k/common-spectral.c
+++ b/drivers/net/wireless/ath/ath9k/common-spectral.c
@@ -716,7 +716,6 @@ void ath9k_cmn_spectral_scan_trigger(struct ath_common *common,
 				 struct ath_spec_scan_priv *spec_priv)
 {
 	struct ath_hw *ah = spec_priv->ah;
-	u32 rxfilter;
 
 	if (IS_ENABLED(CONFIG_ATH9K_TX99))
 		return;
@@ -730,10 +729,8 @@ void ath9k_cmn_spectral_scan_trigger(struct ath_common *common,
 		return;
 
 	ath_ps_ops(common)->wakeup(common);
-	rxfilter = ath9k_hw_getrxfilter(ah);
-	ath9k_hw_setrxfilter(ah, rxfilter |
-				 ATH9K_RX_FILTER_PHYRADAR |
-				 ATH9K_RX_FILTER_PHYERR);
+	ath9k_hw_enable_rxfilter(ah, ATH9K_RX_FILTER_PHYRADAR |
+				     ATH9K_RX_FILTER_PHYERR);
 
 	/* TODO: usually this should not be necessary, but for some reason
 	 * (or in some mode?) the trigger must be called after the
diff --git a/drivers/net/wireless/ath/ath9k/hw.c b/drivers/net/wireless/ath/ath9k/hw.c
index e08ab73fcacb..7cafd6c5870f 100644
--- a/drivers/net/wireless/ath/ath9k/hw.c
+++ b/drivers/net/wireless/ath/ath9k/hw.c
@@ -2905,6 +2905,29 @@ void ath9k_hw_setrxfilter(struct ath_hw *ah, u32 bits)
 }
 EXPORT_SYMBOL(ath9k_hw_setrxfilter);
 
+/**
+ * ath9k_hw_enable_rxfilter() - set RX filter bits without a driver-side read
+ * @ah: the atheros hardware data structure
+ * @bits: ATH9K_RX_FILTER_* bits to set
+ */
+void ath9k_hw_enable_rxfilter(struct ath_hw *ah, u32 bits)
+{
+	u32 phybits = 0;
+
+	if (bits & ATH9K_RX_FILTER_PHYRADAR)
+		phybits |= AR_PHY_ERR_RADAR;
+	if (bits & ATH9K_RX_FILTER_PHYERR)
+		phybits |= AR_PHY_ERR_OFDM_TIMING | AR_PHY_ERR_CCK_TIMING;
+
+	REG_SET_BIT(ah, AR_RX_FILTER, bits);
+
+	if (phybits) {
+		REG_SET_BIT(ah, AR_PHY_ERR, phybits);
+		REG_SET_BIT(ah, AR_RXCFG, AR_RXCFG_ZLFDMA);
+	}
+}
+EXPORT_SYMBOL(ath9k_hw_enable_rxfilter);
+
 bool ath9k_hw_phy_disable(struct ath_hw *ah)
 {
 	if (ath9k_hw_mci_is_enabled(ah))
diff --git a/drivers/net/wireless/ath/ath9k/hw.h b/drivers/net/wireless/ath/ath9k/hw.h
index b942b8303d8f..f102f73a0114 100644
--- a/drivers/net/wireless/ath/ath9k/hw.h
+++ b/drivers/net/wireless/ath/ath9k/hw.h
@@ -1055,6 +1055,7 @@ void ath9k_hw_get_channel_centers(struct ath_hw *ah,
 				  struct chan_centers *centers);
 u32 ath9k_hw_getrxfilter(struct ath_hw *ah);
 void ath9k_hw_setrxfilter(struct ath_hw *ah, u32 bits);
+void ath9k_hw_enable_rxfilter(struct ath_hw *ah, u32 bits);
 bool ath9k_hw_phy_disable(struct ath_hw *ah);
 bool ath9k_hw_disable(struct ath_hw *ah);
 void ath9k_hw_set_txpowerlimit(struct ath_hw *ah, u32 limit, bool test);
-- 
2.55.0