[PATCH v2 0/2] NFC: trf7970a: Add option to reduce antenna gain

[PATCH v2 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>
---
v1 -> v2:
- Added vendor prefix
- Added units

[PATCH v2 1/2] dt-bindings: net/nfc: ti,trf7970a: Add ti,rx-gain-reduction 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..066a7abc41e0 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:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description: |
+      Specify a RX gain reduction to reduce antenna sensitivity with 5dB per
+      increment, with a maximum of 15dB.
+
 required:
   - compatible
   - interrupts
@@ -95,5 +101,6 @@ examples:
             irq-status-read-quirk;
             en2-rf-quirk;
             clock-frequency = <27120000>;
+            ti,rx-gain-reduction = <3>;
         };
     };
-- 
2.39.2

Re: [PATCH v2 1/2] dt-bindings: net/nfc: ti,trf7970a: Add ti,rx-gain-reduction option

[Andrew Lunn]

On Tue, Jun 24, 2025 at 02:42:46PM +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..066a7abc41e0 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:

You should include the units, "ti,rx-gain-reduction-db"

> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    description: |
> +      Specify a RX gain reduction to reduce antenna sensitivity with 5dB per
> +      increment, with a maximum of 15dB.

Given that description i think you can provide a list of values, [0,
5, 10, 15] and the tools will validate values in .dts files.

> +
>  required:
>    - compatible
>    - interrupts
> @@ -95,5 +101,6 @@ examples:
>              irq-status-read-quirk;
>              en2-rf-quirk;
>              clock-frequency = <27120000>;
> +            ti,rx-gain-reduction = <3>;

Err, how does 3 fit into 5dB increments?

	Andrew

[PATCH v2 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 | 86 ++++++++++++++++++++++++++++++++++++------
 1 file changed, 75 insertions(+), 11 deletions(-)

diff --git a/drivers/nfc/trf7970a.c b/drivers/nfc/trf7970a.c
index 9e1a34e23af2..58ea730d1766 100644
--- a/drivers/nfc/trf7970a.c
+++ b/drivers/nfc/trf7970a.c
@@ -274,10 +274,14 @@
 
 #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 +456,8 @@ 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 +557,41 @@ 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 +971,7 @@ 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 +1075,11 @@ 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 +1354,7 @@ 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 +1486,7 @@ 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 +1650,7 @@ 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 +1698,7 @@ 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 +1799,10 @@ 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 +1993,10 @@ 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 +2045,7 @@ 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;
 
 	if (!np) {
 		dev_err(&spi->dev, "No Device Tree entry\n");
@@ -2054,6 +2107,17 @@ static int trf7970a_probe(struct spi_device *spi)
 		trf->modulator_sys_clk_ctrl = 0;
 	}
 
+	if (of_property_read_u32(np, "ti,rx-gain-reduction", &rx_gain_reduction) == 0) {
+		if (rx_gain_reduction > TRF7970A_RX_SPECIAL_SETTINGS_GD_MAX) {
+			dev_warn(trf->dev, "invalid RX gain reduction setting: %u. Limiting to %u\n",
+				 rx_gain_reduction, TRF7970A_RX_SPECIAL_SETTINGS_GD_MAX);
+			rx_gain_reduction = TRF7970A_RX_SPECIAL_SETTINGS_GD_MAX;
+		}
+		trf->rx_gain_reduction = (rx_gain_reduction <<
+			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 v2 1/2] dt-bindings: net/nfc: ti,trf7970a: Add ti,rx-gain-reduction option

[Paul Geurts]

> On Tue, Jun 24, 2025 at 02:42:46PM +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..066a7abc41e0 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:
> 
> You should include the units, "ti,rx-gain-reduction-db"

Well, Currently it's not really a dB value (see below).

> 
> > +    $ref: /schemas/types.yaml#/definitions/uint32
> > +    description: |
> > +      Specify a RX gain reduction to reduce antenna sensitivity with 5dB per
> > +      increment, with a maximum of 15dB.
> 
> Given that description i think you can provide a list of values, [0,
> 5, 10, 15] and the tools will validate values in .dts files.
> 
> > +
> >  required:
> >    - compatible
> >    - interrupts
> > @@ -95,5 +101,6 @@ examples:
> >              irq-status-read-quirk;
> >              en2-rf-quirk;
> >              clock-frequency = <27120000>;
> > +            ti,rx-gain-reduction = <3>;
> 
> Err, how does 3 fit into 5dB increments?

I implemented it in a way that the value of ti,rx-gain-reduction is programmed
directly into the RX_GAIN reduction register, and there it means 5 dB/LSB. My
description probably was not clear enough about that. So a value of 3 here actually
means 15dB.
So I could either improve the description here that this is the case, or make the
value in here in actual dB, and do some calculations in the driver. What has your
preference?

> 
> 	Andrew
> 

Thanks!

Paul

Re: [PATCH v2 1/2] dt-bindings: net/nfc: ti,trf7970a: Add ti,rx-gain-reduction option

[Andrew Lunn]

> > You should include the units, "ti,rx-gain-reduction-db"
> 
> Well, Currently it's not really a dB value (see below).
> 
> > 
> > > +    $ref: /schemas/types.yaml#/definitions/uint32
> > > +    description: |
> > > +      Specify a RX gain reduction to reduce antenna sensitivity with 5dB per
> > > +      increment, with a maximum of 15dB.
> > 
> > Given that description i think you can provide a list of values, [0,
> > 5, 10, 15] and the tools will validate values in .dts files.
> > 
> > > +
> > >  required:
> > >    - compatible
> > >    - interrupts
> > > @@ -95,5 +101,6 @@ examples:
> > >              irq-status-read-quirk;
> > >              en2-rf-quirk;
> > >              clock-frequency = <27120000>;
> > > +            ti,rx-gain-reduction = <3>;
> > 
> > Err, how does 3 fit into 5dB increments?
> 
> I implemented it in a way that the value of ti,rx-gain-reduction is programmed
> directly into the RX_GAIN reduction register, and there it means 5 dB/LSB. My
> description probably was not clear enough about that. So a value of 3 here actually
> means 15dB.
> So I could either improve the description here that this is the case, or make the
> value in here in actual dB, and do some calculations in the driver. What has your
> preference?

DT should use SI units, Volts, Amps, degrees C, meters, etc. The
driver then should do whatever conversion is needed to convert to
hardware register values.

Less important, but i'm also wondering if this should be negative,
ti,rx-gain-db, with a value of -15. You say this receiver is overly
sensitive, so you need to reduce the gain. But are there TI devices
where you can actually increase the gain? Ideally the property should
be generic and be able to cover that use case as well.

    Andrew

---
pw-bot: cr

Re: [PATCH v2 1/2] dt-bindings: net/nfc: ti,trf7970a: Add ti,rx-gain-reduction option

[Paul Geurts]

> > > You should include the units, "ti,rx-gain-reduction-db"
> > 
> > Well, Currently it's not really a dB value (see below).
> > 
> > > 
> > > > +    $ref: /schemas/types.yaml#/definitions/uint32
> > > > +    description: |
> > > > +      Specify a RX gain reduction to reduce antenna sensitivity with 5dB per
> > > > +      increment, with a maximum of 15dB.
> > > 
> > > Given that description i think you can provide a list of values, [0, 
> > > 5, 10, 15] and the tools will validate values in .dts files.
> > > 
> > > > +
> > > >  required:
> > > >    - compatible
> > > >    - interrupts
> > > > @@ -95,5 +101,6 @@ examples:
> > > >              irq-status-read-quirk;
> > > >              en2-rf-quirk;
> > > >              clock-frequency = <27120000>;
> > > > +            ti,rx-gain-reduction = <3>;
> > > 
> > > Err, how does 3 fit into 5dB increments?
> > 
> > I implemented it in a way that the value of ti,rx-gain-reduction is 
> > programmed directly into the RX_GAIN reduction register, and there it 
> > means 5 dB/LSB. My description probably was not clear enough about 
> > that. So a value of 3 here actually means 15dB.
> > So I could either improve the description here that this is the case, 
> > or make the value in here in actual dB, and do some calculations in 
> > the driver. What has your preference?
> 
> DT should use SI units, Volts, Amps, degrees C, meters, etc. The driver then should do whatever conversion is needed to convert to hardware register values.
> 
> Less important, but i'm also wondering if this should be negative, ti,rx-gain-db, with a value of -15. You say this receiver is overly sensitive, so you need to reduce the gain. But are there TI devices where you can actually increase the gain? Ideally the property should be generic and be able to cover that use case as well.

As far as I am aware, I cannot put a negative number in a dts property. I can interpret the property as s32, but that would mean I need to put it in the dts like

ti,rx-gain = <0xfffffff1>;

which looks like a bad idea. I will just convert it to a dB value for v3.

> 
>     Andrew
> 
> ---
> pw-bot: cr
> 

Thanks!

Paul