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NFC: trf7970a: Ignore antenna noise when checking for RF field

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[ Upstream commit a9bc28aa4e ]

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: 851ee3cbf8 ("NFC: trf7970a: Don't turn on RF if there is already an RF field")
Signed-off-by: Paul Geurts <paul.geurts@prodrive-technologies.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
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>
This commit is contained in:
Paul Geurts
2026-05-23 13:03:28 +02:00
committed by Greg Kroah-Hartman
parent 17e23e8150
commit 0d0dd383ac
1 changed files with 2 additions and 1 deletions
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drivers/nfc/trf7970a.c
+2 -1
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@@ -311,6 +311,7 @@
#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)
@@ -1253,7 +1254,7 @@ 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;