7.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Paul Geurts <redacted>

[ Upstream commit a9bc28aa4e64320668131349436a650bf42591a5 ]

The main channel Received Signal Strength Indicator (RSSI) measurement
is used to determine whether an RF field is present or not. RSSI != 0
is interpreted as an RF Field is present. This does not take RF noise
and measurement inaccuracy into account, and results in false positives
in the field.

Define a noise level and make sure the RF field is only interpreted as
present when the RSSI is above the noise level.

Fixes: 851ee3cbf850 ("NFC: trf7970a: Don't turn on RF if there is already an RF field")
Signed-off-by: Paul Geurts <redacted>
Reviewed-by: Krzysztof Kozlowski <redacted>
Reviewed-by: Mark Greer <mgreer@animalcreek.com>
Link: https://patch.msgid.link/20260422100930.581237-1-paul.geurts@prodrive-technologies.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/nfc/trf7970a.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/nfc/trf7970a.c b/drivers/nfc/trf7970a.c
index d17c701c7888b..08c27bb438b59 100644
--- a/drivers/nfc/trf7970a.c
+++ b/drivers/nfc/trf7970a.c

@@ -317,6 +317,7 @@
 #define TRF7970A_RSSI_OSC_STATUS_RSSI_MASK	(BIT(2) | BIT(1) | BIT(0))
 #define TRF7970A_RSSI_OSC_STATUS_RSSI_X_MASK	(BIT(5) | BIT(4) | BIT(3))
 #define TRF7970A_RSSI_OSC_STATUS_RSSI_OSC_OK	BIT(6)
+#define TRF7970A_RSSI_OSC_STATUS_RSSI_NOISE_LEVEL	1
 
 #define TRF7970A_SPECIAL_FCN_REG1_COL_7_6		BIT(0)
 #define TRF7970A_SPECIAL_FCN_REG1_14_ANTICOLL		BIT(1)

@@ -1300,7 +1301,7 @@ static int trf7970a_is_rf_field(struct trf7970a *trf, bool *is_rf_field)
 	if (ret)
 		return ret;
 
-	if (rssi & TRF7970A_RSSI_OSC_STATUS_RSSI_MASK)
+	if ((rssi & TRF7970A_RSSI_OSC_STATUS_RSSI_MASK) > TRF7970A_RSSI_OSC_STATUS_RSSI_NOISE_LEVEL)
 		*is_rf_field = true;
 	else
 		*is_rf_field = false;

-- 
2.53.0