cc2520: Add support for CC2591 amplifier.

The TI CC2521 is an RF power amplifier that is designed to interface
with the CC2520. Conveniently, it directly interfaces with the CC2520
and does not require any pins to be connected to a
microcontroller/processor. Adding a CC2591 increases the CC2520's range,
which is useful for border router and other wall-powered applications.

Using the CC2591 with the CC2520 requires configuring the CC2520 GPIOs
that are connected to the CC2591 to correctly set the CC2591 into TX and
RX modes. Further, TI recommends that the CC2520_TXPOWER and
CC2520_AGCCTRL1 registers are set differently to maximize the CC2591's
performance. These settings are covered in TI Application Note AN065.

This patch adds an optional `amplified` field to the cc2520 entry in the
device tree. If present, the CC2520 will be configured to operate with a
CC2591.

The expected pin mapping is:
CC2520 GPIO0 --> CC2591 EN
CC2520 GPIO5 --> CC2591 PAEN

Signed-off-by: Brad Campbell <[e-mail]>
Acked-by: Varka Bhadram <[e-mail]>
Signed-off-by: Marcel Holtmann <[e-mail]>

Documentation/devicetree/bindings/net/ieee802154/cc2520.txt

···
 	- cca-gpio:		GPIO spec for the CCA pin
 	- vreg-gpio:		GPIO spec for the VREG pin
 	- reset-gpio:		GPIO spec for the RESET pin
+Optional properties:
+	- amplified:		include if the CC2520 is connected to a CC2591 amplifier
+
 Example:
 	cc2520@0 {
 		compatible = "ti,cc2520";
 		reg = <0>;
 		spi-max-frequency = <4000000>;
+		amplified;
 		pinctrl-names = "default";
 		pinctrl-0 = <&cc2520_cape_pins>;
 		fifo-gpio = <&gpio1 18 0>;

drivers/net/ieee802154/cc2520.c

···
 	pdata->vreg = of_get_named_gpio(np, "vreg-gpio", 0);
 	pdata->reset = of_get_named_gpio(np, "reset-gpio", 0);
 
+	pdata->amplified = of_property_read_bool(np, "amplified");
+
 	return 0;
 }
 
···
 	u8 status = 0, state = 0xff;
 	int ret;
 	int timeout = 100;
+	struct cc2520_platform_data pdata;
+
+	ret = cc2520_get_platform_data(priv->spi, &pdata);
+	if (ret)
+		goto err_ret;
 
 	ret = cc2520_read_register(priv, CC2520_FSMSTAT1, &state);
 	if (ret)
···
 
 	dev_vdbg(&priv->spi->dev, "oscillator brought up\n");
 
-	/* Registers default value: section 28.1 in Datasheet */
-	ret = cc2520_write_register(priv, CC2520_TXPOWER, 0xF7);
-	if (ret)
-		goto err_ret;
+	/* If the CC2520 is connected to a CC2591 amplifier, we must both
+	 * configure GPIOs on the CC2520 to correctly configure the CC2591
+	 * and change a couple settings of the CC2520 to work with the
+	 * amplifier. See section 8 page 17 of TI application note AN065.
+	 * http://www.ti.com/lit/an/swra229a/swra229a.pdf
+	 */
+	if (pdata.amplified) {
+		ret = cc2520_write_register(priv, CC2520_TXPOWER, 0xF9);
+		if (ret)
+			goto err_ret;
 
+		ret = cc2520_write_register(priv, CC2520_AGCCTRL1, 0x16);
+		if (ret)
+			goto err_ret;
+
+		ret = cc2520_write_register(priv, CC2520_GPIOCTRL0, 0x46);
+		if (ret)
+			goto err_ret;
+
+		ret = cc2520_write_register(priv, CC2520_GPIOCTRL5, 0x47);
+		if (ret)
+			goto err_ret;
+
+		ret = cc2520_write_register(priv, CC2520_GPIOPOLARITY, 0x1e);
+		if (ret)
+			goto err_ret;
+
+		ret = cc2520_write_register(priv, CC2520_TXCTRL, 0xc1);
+		if (ret)
+			goto err_ret;
+	} else {
+		ret = cc2520_write_register(priv, CC2520_TXPOWER, 0xF7);
+		if (ret)
+			goto err_ret;
+
+		ret = cc2520_write_register(priv, CC2520_AGCCTRL1, 0x11);
+		if (ret)
+			goto err_ret;
+	}
+
+	/* Registers default value: section 28.1 in Datasheet */
 	ret = cc2520_write_register(priv, CC2520_CCACTRL0, 0x1A);
 	if (ret)
 		goto err_ret;
···
 		goto err_ret;
 
 	ret = cc2520_write_register(priv, CC2520_FSCAL1, 0x2b);
-	if (ret)
-		goto err_ret;
-
-	ret = cc2520_write_register(priv, CC2520_AGCCTRL1, 0x11);
 	if (ret)
 		goto err_ret;
 

include/linux/spi/cc2520.h

···
 	int sfd;
 	int reset;
 	int vreg;
+	bool amplified;
 };
 
 #endif