[PATCH v3 0/2] NFC: trf7970a: Add option to reduce antenna gain

[PATCH v3 0/2] NFC: trf7970a: Add option to reduce antenna gain

[Paul Geurts]

The TRF7970a device is sensitive to RF disturbances, which can make it
hard to pass some EMC immunity tests. By reducing the RX antenna gain,
the device becomes less sensitive to EMC disturbances, as a trade-off
against antenna performance.

Signed-off-by: Paul Geurts <paul.geurts@prodrive-technologies.com>
---
v2 -> v3:
- User SI units for the DT property, instead of the direct register
  value
v1 -> v2:
- Added vendor prefix
- Added units

[PATCH v3 1/2] dt-bindings: net/nfc: ti,trf7970a: Add ti,rx-gain-reduction-db option

[Paul Geurts]

Add option to reduce the RX antenna gain to be able to reduce the
sensitivity.

Signed-off-by: Paul Geurts <paul.geurts@prodrive-technologies.com>
---
 Documentation/devicetree/bindings/net/nfc/ti,trf7970a.yaml | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Documentation/devicetree/bindings/net/nfc/ti,trf7970a.yaml b/Documentation/devicetree/bindings/net/nfc/ti,trf7970a.yaml
index d0332eb76ad2..5f49bd9ac5e6 100644
--- a/Documentation/devicetree/bindings/net/nfc/ti,trf7970a.yaml
+++ b/Documentation/devicetree/bindings/net/nfc/ti,trf7970a.yaml
@@ -55,6 +55,12 @@ properties:
     description: |
       Regulator for supply voltage to VIN pin
 
+  ti,rx-gain-reduction-db:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description: |
+      Specify an RX gain reduction to reduce antenna sensitivity with 5dB per
+      increment, with a maximum of 15dB. Supported values: [0, 5, 10, 15].
+
 required:
   - compatible
   - interrupts
@@ -95,5 +101,6 @@ examples:
             irq-status-read-quirk;
             en2-rf-quirk;
             clock-frequency = <27120000>;
+            ti,rx-gain-reduction-db = <15>;
         };
     };
-- 
2.39.2

[PATCH v3 2/2] NFC: trf7970a: Create device-tree parameter for RX gain reduction

[Paul Geurts]

The TRF7970a device is sensitive to RF disturbances, which can make it
hard to pass some EMC immunity tests. By reducing the RX antenna gain,
the device becomes less sensitive to EMC disturbances, as a trade-off
against antenna performance.

Add a device tree option to select RX gain reduction to improve EMC
performance.

Selecting a communication standard in the ISO control register resets
the RX antenna gain settings. Therefore set the RX gain reduction
everytime the ISO control register changes, when the option is used.

Signed-off-by: Paul Geurts <paul.geurts@prodrive-technologies.com>
---
 drivers/nfc/trf7970a.c | 91 +++++++++++++++++++++++++++++++++++++-----
 1 file changed, 80 insertions(+), 11 deletions(-)

diff --git a/drivers/nfc/trf7970a.c b/drivers/nfc/trf7970a.c
index 9e1a34e23af2..d17c701c7888 100644
--- a/drivers/nfc/trf7970a.c
+++ b/drivers/nfc/trf7970a.c
@@ -272,12 +272,18 @@
 #define TRF7970A_MODULATOR_EN_OOK		BIT(6)
 #define TRF7970A_MODULATOR_27MHZ		BIT(7)
 
+#define TRF7970A_RX_GAIN_REDUCTION_MAX_DB	15
+#define TRF7970A_RX_GAIN_REDUCTION_DB_PER_LSB	5
 #define TRF7970A_RX_SPECIAL_SETTINGS_NO_LIM	BIT(0)
 #define TRF7970A_RX_SPECIAL_SETTINGS_AGCR	BIT(1)
-#define TRF7970A_RX_SPECIAL_SETTINGS_GD_0DB	(0x0 << 2)
-#define TRF7970A_RX_SPECIAL_SETTINGS_GD_5DB	(0x1 << 2)
-#define TRF7970A_RX_SPECIAL_SETTINGS_GD_10DB	(0x2 << 2)
-#define TRF7970A_RX_SPECIAL_SETTINGS_GD_15DB	(0x3 << 2)
+#define TRF7970A_RX_SPECIAL_SETTINGS_GD_SHIFT	2
+#define TRF7970A_RX_SPECIAL_SETTINGS_GD_MAX	(0x3)
+#define TRF7970A_RX_SPECIAL_SETTINGS_GD_MASK	(TRF7970A_RX_SPECIAL_SETTINGS_GD_MAX << \
+							TRF7970A_RX_SPECIAL_SETTINGS_GD_SHIFT)
+#define TRF7970A_RX_SPECIAL_SETTINGS_GD_0DB	(0x0 << TRF7970A_RX_SPECIAL_SETTINGS_GD_SHIFT)
+#define TRF7970A_RX_SPECIAL_SETTINGS_GD_5DB	(0x1 << TRF7970A_RX_SPECIAL_SETTINGS_GD_SHIFT)
+#define TRF7970A_RX_SPECIAL_SETTINGS_GD_10DB	(0x2 << TRF7970A_RX_SPECIAL_SETTINGS_GD_SHIFT)
+#define TRF7970A_RX_SPECIAL_SETTINGS_GD_15DB	(0x3 << TRF7970A_RX_SPECIAL_SETTINGS_GD_SHIFT)
 #define TRF7970A_RX_SPECIAL_SETTINGS_HBT	BIT(4)
 #define TRF7970A_RX_SPECIAL_SETTINGS_M848	BIT(5)
 #define TRF7970A_RX_SPECIAL_SETTINGS_C424	BIT(6)
@@ -452,6 +458,8 @@ struct trf7970a {
 	unsigned int			timeout;
 	bool				ignore_timeout;
 	struct delayed_work		timeout_work;
+	u8				rx_gain_reduction;
+	bool			custom_rx_gain_reduction;
 };
 
 static int trf7970a_cmd(struct trf7970a *trf, u8 opcode)
@@ -551,6 +559,41 @@ static int trf7970a_read_irqstatus(struct trf7970a *trf, u8 *status)
 	return ret;
 }
 
+static int trf7970a_update_rx_gain_reduction(struct trf7970a *trf)
+{
+	int ret = 0;
+	u8 reg;
+
+	if (!trf->custom_rx_gain_reduction)
+		return 0;
+
+	ret = trf7970a_read(trf, TRF7970A_RX_SPECIAL_SETTINGS, &reg);
+	if (ret)
+		return ret;
+	reg &= ~(TRF7970A_RX_SPECIAL_SETTINGS_GD_MASK);
+	reg |= trf->rx_gain_reduction;
+
+	ret = trf7970a_write(trf, TRF7970A_RX_SPECIAL_SETTINGS, reg);
+
+	return ret;
+}
+
+static int trf7970a_update_iso_ctrl_register(struct trf7970a *trf, u8 iso_ctrl)
+{
+	int ret;
+
+	ret = trf7970a_write(trf, TRF7970A_ISO_CTRL, iso_ctrl);
+	if (ret)
+		return ret;
+	/*
+	 * Every time the ISO_CTRL register is written, the RX special setting register is reset by
+	 * the chip. When a custom gain reguduction is required, it should be rewritten now.
+	 */
+	ret = trf7970a_update_rx_gain_reduction(trf);
+
+	return ret;
+}
+
 static int trf7970a_read_target_proto(struct trf7970a *trf, u8 *target_proto)
 {
 	int ret;
@@ -930,8 +973,7 @@ static irqreturn_t trf7970a_irq(int irq, void *dev_id)
 			}
 
 			if (iso_ctrl != trf->iso_ctrl) {
-				ret = trf7970a_write(trf, TRF7970A_ISO_CTRL,
-						     iso_ctrl);
+				ret = trf7970a_update_iso_ctrl_register(trf, iso_ctrl);
 				if (ret)
 					goto err_unlock_exit;
 
@@ -1035,6 +1077,11 @@ static int trf7970a_init(struct trf7970a *trf)
 	if (ret)
 		goto err_out;
 
+	/* Set the gain reduction after soft init */
+	ret = trf7970a_update_rx_gain_reduction(trf);
+	if (ret)
+		goto err_out;
+
 	ret = trf7970a_cmd(trf, TRF7970A_CMD_IDLE);
 	if (ret)
 		goto err_out;
@@ -1309,7 +1356,7 @@ static int trf7970a_in_config_framing(struct trf7970a *trf, int framing)
 	}
 
 	if (iso_ctrl != trf->iso_ctrl) {
-		ret = trf7970a_write(trf, TRF7970A_ISO_CTRL, iso_ctrl);
+		ret = trf7970a_update_iso_ctrl_register(trf, iso_ctrl);
 		if (ret)
 			return ret;
 
@@ -1441,7 +1488,7 @@ static int trf7970a_per_cmd_config(struct trf7970a *trf,
 		}
 
 		if (iso_ctrl != trf->iso_ctrl) {
-			ret = trf7970a_write(trf, TRF7970A_ISO_CTRL, iso_ctrl);
+			ret = trf7970a_update_iso_ctrl_register(trf, iso_ctrl);
 			if (ret)
 				return ret;
 
@@ -1605,8 +1652,7 @@ static int trf7970a_tg_config_rf_tech(struct trf7970a *trf, int tech)
 	 */
 	if ((trf->framing == NFC_DIGITAL_FRAMING_NFC_DEP_ACTIVATED) &&
 	    (trf->iso_ctrl_tech != trf->iso_ctrl)) {
-		ret = trf7970a_write(trf, TRF7970A_ISO_CTRL,
-				     trf->iso_ctrl_tech);
+		ret = trf7970a_update_iso_ctrl_register(trf, trf->iso_ctrl_tech);
 
 		trf->iso_ctrl = trf->iso_ctrl_tech;
 	}
@@ -1654,7 +1700,7 @@ static int trf7970a_tg_config_framing(struct trf7970a *trf, int framing)
 	trf->framing = framing;
 
 	if (iso_ctrl != trf->iso_ctrl) {
-		ret = trf7970a_write(trf, TRF7970A_ISO_CTRL, iso_ctrl);
+		ret = trf7970a_update_iso_ctrl_register(trf, iso_ctrl);
 		if (ret)
 			return ret;
 
@@ -1755,6 +1801,10 @@ static int _trf7970a_tg_listen(struct nfc_digital_dev *ddev, u16 timeout,
 	if (ret)
 		goto out_err;
 
+	ret = trf7970a_update_rx_gain_reduction(trf);
+	if (ret)
+		goto out_err;
+
 	ret = trf7970a_write(trf, TRF7970A_REG_IO_CTRL,
 			     trf->io_ctrl | TRF7970A_REG_IO_CTRL_VRS(0x1));
 	if (ret)
@@ -1945,6 +1995,10 @@ static int trf7970a_startup(struct trf7970a *trf)
 	if (ret)
 		return ret;
 
+	ret = trf7970a_update_rx_gain_reduction(trf);
+	if (ret)
+		return ret;
+
 	pm_runtime_set_active(trf->dev);
 	pm_runtime_enable(trf->dev);
 	pm_runtime_mark_last_busy(trf->dev);
@@ -1993,6 +2047,7 @@ static int trf7970a_probe(struct spi_device *spi)
 	struct trf7970a *trf;
 	int uvolts, autosuspend_delay, ret;
 	u32 clk_freq = TRF7970A_13MHZ_CLOCK_FREQUENCY;
+	u32 rx_gain_reduction_db;
 
 	if (!np) {
 		dev_err(&spi->dev, "No Device Tree entry\n");
@@ -2054,6 +2109,20 @@ static int trf7970a_probe(struct spi_device *spi)
 		trf->modulator_sys_clk_ctrl = 0;
 	}
 
+	if (of_property_read_u32(np, "ti,rx-gain-reduction-db", &rx_gain_reduction_db) == 0) {
+		if (rx_gain_reduction_db > TRF7970A_RX_GAIN_REDUCTION_MAX_DB) {
+			dev_warn(trf->dev, "RX Gain reduction too high. Ignored\n");
+		} else if ((rx_gain_reduction_db % TRF7970A_RX_GAIN_REDUCTION_DB_PER_LSB)) {
+			dev_warn(trf->dev, "RX Gain must be set in 5 dB increments. Ignored\n");
+		} else {
+			dev_dbg(trf->dev, "RX gain set to -%udB\n", rx_gain_reduction_db);
+			trf->rx_gain_reduction = ((rx_gain_reduction_db /
+				TRF7970A_RX_GAIN_REDUCTION_DB_PER_LSB) <<
+				TRF7970A_RX_SPECIAL_SETTINGS_GD_SHIFT);
+			trf->custom_rx_gain_reduction = true;
+		}
+	}
+
 	ret = devm_request_threaded_irq(trf->dev, spi->irq, NULL,
 					trf7970a_irq,
 					IRQF_TRIGGER_RISING | IRQF_ONESHOT,
-- 
2.39.2

Re: [PATCH v3 1/2] dt-bindings: net/nfc: ti,trf7970a: Add ti,rx-gain-reduction-db option

[Krzysztof Kozlowski]

On Thu, Jun 26, 2025 at 04:12:41PM +0200, Paul Geurts wrote:
> Add option to reduce the RX antenna gain to be able to reduce the
> sensitivity.
> 
> Signed-off-by: Paul Geurts <paul.geurts@prodrive-technologies.com>
> ---
>  Documentation/devicetree/bindings/net/nfc/ti,trf7970a.yaml | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/net/nfc/ti,trf7970a.yaml b/Documentation/devicetree/bindings/net/nfc/ti,trf7970a.yaml
> index d0332eb76ad2..5f49bd9ac5e6 100644
> --- a/Documentation/devicetree/bindings/net/nfc/ti,trf7970a.yaml
> +++ b/Documentation/devicetree/bindings/net/nfc/ti,trf7970a.yaml
> @@ -55,6 +55,12 @@ properties:
>      description: |
>        Regulator for supply voltage to VIN pin
>  
> +  ti,rx-gain-reduction-db:

I'll add db unit to the dtschema.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>

Best regards,
Krzysztof

Re: [PATCH v3 2/2] NFC: trf7970a: Create device-tree parameter for RX gain reduction

[Krzysztof Kozlowski]

On Thu, Jun 26, 2025 at 04:12:42PM +0200, Paul Geurts wrote:
> The TRF7970a device is sensitive to RF disturbances, which can make it
> hard to pass some EMC immunity tests. By reducing the RX antenna gain,
> the device becomes less sensitive to EMC disturbances, as a trade-off
> against antenna performance.
> 
> Add a device tree option to select RX gain reduction to improve EMC
> performance.
> 
> Selecting a communication standard in the ISO control register resets
> the RX antenna gain settings. Therefore set the RX gain reduction
> everytime the ISO control register changes, when the option is used.
> 
> Signed-off-by: Paul Geurts <paul.geurts@prodrive-technologies.com>
> ---
>  drivers/nfc/trf7970a.c | 91 +++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 80 insertions(+), 11 deletions(-)

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>

Best regards,
Krzysztof

Re: [PATCH v3 0/2] NFC: trf7970a: Add option to reduce antenna gain

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Thu, 26 Jun 2025 16:12:40 +0200 you wrote:
> The TRF7970a device is sensitive to RF disturbances, which can make it
> hard to pass some EMC immunity tests. By reducing the RX antenna gain,
> the device becomes less sensitive to EMC disturbances, as a trade-off
> against antenna performance.
> 
> Signed-off-by: Paul Geurts <paul.geurts@prodrive-technologies.com>
> 
> [...]

Here is the summary with links:
  - [v3,1/2] dt-bindings: net/nfc: ti,trf7970a: Add ti,rx-gain-reduction-db option
    https://git.kernel.org/netdev/net-next/c/2bee162a28fb
  - [v3,2/2] NFC: trf7970a: Create device-tree parameter for RX gain reduction
    https://git.kernel.org/netdev/net-next/c/5d69351820ea

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html

Re: [PATCH v3 1/2] dt-bindings: net/nfc: ti,trf7970a: Add ti,rx-gain-reduction-db option

[Krzysztof Kozlowski]

On 27/06/2025 09:10, Krzysztof Kozlowski wrote:
> On Thu, Jun 26, 2025 at 04:12:41PM +0200, Paul Geurts wrote:
>> Add option to reduce the RX antenna gain to be able to reduce the
>> sensitivity.
>>
>> Signed-off-by: Paul Geurts <paul.geurts@prodrive-technologies.com>
>> ---
>>  Documentation/devicetree/bindings/net/nfc/ti,trf7970a.yaml | 7 +++++++
>>  1 file changed, 7 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/net/nfc/ti,trf7970a.yaml b/Documentation/devicetree/bindings/net/nfc/ti,trf7970a.yaml
>> index d0332eb76ad2..5f49bd9ac5e6 100644
>> --- a/Documentation/devicetree/bindings/net/nfc/ti,trf7970a.yaml
>> +++ b/Documentation/devicetree/bindings/net/nfc/ti,trf7970a.yaml
>> @@ -55,6 +55,12 @@ properties:
>>      description: |
>>        Regulator for supply voltage to VIN pin
>>  
>> +  ti,rx-gain-reduction-db:
> 
> I'll add db unit to the dtschema.
> 
> Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>

BTW, I found your patchset only via patchwork, because Gmail flagged
your entire v3 and others as spam. You might need to check your SMTP
setup. I see DMARC failure from google in the headers:

Authentication-Results: mx.google.com;
       spf=pass (google.com: domain of
srs0=m3n1=zj=prodrive-technologies.com=paul.geurts@kernel.org designates
147........ as permitted sender)
smtp.mailfrom="SRS0=m3n1=ZJ=prodrive-technologies.com=paul.geurts@kernel.org";
       dmarc=fail (p=REJECT sp=REJECT dis=QUARANTINE)
header.from=prodrive-technologies.com


Maybe you sent via kernel.org something with different address? Actually
this looks like that - your From does not match kernel.org at all.
Rules are quite strict recently and for example you cannot use
non-kernel.org SMTP server for kernel.org accounts (see kernel users wiki).

Anyway, likely any other future patches or such patches to other people
to end up in spam as well.

Best regards,
Krzysztof

RE: [PATCH v3 1/2] dt-bindings: net/nfc: ti,trf7970a: Add ti,rx-gain-reduction-db option

[Paul Geurts]

> On 27/06/2025 09:10, Krzysztof Kozlowski wrote:
>> On Thu, Jun 26, 2025 at 04:12:41PM +0200, Paul Geurts wrote:
>>> Add option to reduce the RX antenna gain to be able to reduce the 
>>> sensitivity.
>>>
>>> Signed-off-by: Paul Geurts <paul.geurts@prodrive-technologies.com>
>>> ---
>>>  Documentation/devicetree/bindings/net/nfc/ti,trf7970a.yaml | 7 
>>> +++++++
>>>  1 file changed, 7 insertions(+)
>>>
>>> diff --git 
>>> a/Documentation/devicetree/bindings/net/nfc/ti,trf7970a.yaml 
>>> b/Documentation/devicetree/bindings/net/nfc/ti,trf7970a.yaml
>>> index d0332eb76ad2..5f49bd9ac5e6 100644
>>> --- a/Documentation/devicetree/bindings/net/nfc/ti,trf7970a.yaml
>>> +++ b/Documentation/devicetree/bindings/net/nfc/ti,trf7970a.yaml
>>> @@ -55,6 +55,12 @@ properties:
>>>      description: |
>>>        Regulator for supply voltage to VIN pin
>>>  
>>> +  ti,rx-gain-reduction-db:
>> 
>> I'll add db unit to the dtschema.
>> 
>> Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
>
> BTW, I found your patchset only via patchwork, because Gmail flagged your entire v3 and others as spam. You might need to check your SMTP setup. I see DMARC failure from google in the headers:
>
> Authentication-Results: mx.google.com;
>       spf=pass (google.com: domain of
> srs0=m3n1=zj=prodrive-technologies.com=paul.geurts@kernel.org designates 147........ as permitted sender) smtp.mailfrom="SRS0=m3n1=ZJ=prodrive-technologies.com=paul.geurts@kernel.org";
>        dmarc=fail (p=REJECT sp=REJECT dis=QUARANTINE) header.from=prodrive-technologies.com
>
>
> Maybe you sent via kernel.org something with different address? Actually this looks like that - your From does not match kernel.org at all.
> Rules are quite strict recently and for example you cannot use non-kernel.org SMTP server for kernel.org accounts (see kernel users wiki).
> 
> Anyway, likely any other future patches or such patches to other people to end up in spam as well.

Thanks for the heads up! I'll contact our IT dept. to look into that. And thanks for the review!

>
> Best regards,
> Krzysztof

Paul