at86rf230: add support for external xtal trim

This patch adds support for setting the xtal trim register. Some at86rf2xx
transceiver boards needs fine tuning the xtal capacitor.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

diff --git a/Documentation/devicetree/bindings/net/ieee802154/at86rf230.txt b/Documentation/devicetree/bindings/net/ieee802154/at86rf230.txt
index d3bbdded4cbe8db90ce49648e95b6476212f27f6..1ae5100fea1462f0e58e1b5425c73f73b007ef1a 100644 (file)
--- a/Documentation/devicetree/bindings/net/ieee802154/at86rf230.txt
+++ b/Documentation/devicetree/bindings/net/ieee802154/at86rf230.txt
@@ -11,6 +11,8 @@ Required properties:
 Optional properties:
   - reset-gpio:                GPIO spec for the rstn pin
   - sleep-gpio:                GPIO spec for the slp_tr pin
+  - xtal-trim:         u8 value for fine tuning the internal capacitance
+                       arrays of xtal pins: 0 = +0 pF, 0xf = +4.5 pF
 
 Example:
 
@@ -20,4 +22,5 @@ Example:
                reg = <0>;
                interrupts = <19 1>;
                interrupt-parent = <&gpio3>;
+               xtal-trim = /bits/ 8 <0x06>;
        };

diff --git a/drivers/net/ieee802154/at86rf230.c b/drivers/net/ieee802154/at86rf230.c
index 9888b7ff24bcbb60e2b190831d6e2c88c8f5caab..c1323e5cdd0ce826e89cdd86008ce018cf1d7f45 100644 (file)
--- a/drivers/net/ieee802154/at86rf230.c
+++ b/drivers/net/ieee802154/at86rf230.c
@@ -1315,7 +1315,7 @@ static struct at86rf2xx_chip_data at86rf212_data = {
        .get_desense_steps = at86rf212_get_desens_steps
 };
 
-static int at86rf230_hw_init(struct at86rf230_local *lp)
+static int at86rf230_hw_init(struct at86rf230_local *lp, u8 xtal_trim)
 {
        int rc, irq_type, irq_pol = IRQ_ACTIVE_HIGH;
        unsigned int dvdd;
@@ -1362,6 +1362,45 @@ static int at86rf230_hw_init(struct at86rf230_local *lp)
        usleep_range(lp->data->t_sleep_cycle,
                     lp->data->t_sleep_cycle + 100);
 
+       /* xtal_trim value is calculated by:
+        * CL = 0.5 * (CX + CTRIM + CPAR)
+        *
+        * whereas:
+        * CL = capacitor of used crystal
+        * CX = connected capacitors at xtal pins
+        * CPAR = in all at86rf2xx datasheets this is a constant value 3 pF,
+        *        but this is different on each board setup. You need to fine
+        *        tuning this value via CTRIM.
+        * CTRIM = variable capacitor setting. Resolution is 0.3 pF range is
+        *         0 pF upto 4.5 pF.
+        *
+        * Examples:
+        * atben transceiver:
+        *
+        * CL = 8 pF
+        * CX = 12 pF
+        * CPAR = 3 pF (We assume the magic constant from datasheet)
+        * CTRIM = 0.9 pF
+        *
+        * (12+0.9+3)/2 = 7.95 which is nearly at 8 pF
+        *
+        * xtal_trim = 0x3
+        *
+        * openlabs transceiver:
+        *
+        * CL = 16 pF
+        * CX = 22 pF
+        * CPAR = 3 pF (We assume the magic constant from datasheet)
+        * CTRIM = 4.5 pF
+        *
+        * (22+4.5+3)/2 = 14.75 which is the nearest value to 16 pF
+        *
+        * xtal_trim = 0xf
+        */
+       rc = at86rf230_write_subreg(lp, SR_XTAL_TRIM, xtal_trim);
+       if (rc)
+               return rc;
+
        rc = at86rf230_read_subreg(lp, SR_DVDD_OK, &dvdd);
        if (rc)
                return rc;
@@ -1378,9 +1417,11 @@ static int at86rf230_hw_init(struct at86rf230_local *lp)
 }
 
 static int
-at86rf230_get_pdata(struct spi_device *spi, int *rstn, int *slp_tr)
+at86rf230_get_pdata(struct spi_device *spi, int *rstn, int *slp_tr,
+                   u8 *xtal_trim)
 {
        struct at86rf230_platform_data *pdata = spi->dev.platform_data;
+       int ret;
 
        if (!IS_ENABLED(CONFIG_OF) || !spi->dev.of_node) {
                if (!pdata)
@@ -1388,11 +1429,15 @@ at86rf230_get_pdata(struct spi_device *spi, int *rstn, int *slp_tr)
 
                *rstn = pdata->rstn;
                *slp_tr = pdata->slp_tr;
+               *xtal_trim = pdata->xtal_trim;
                return 0;
        }
 
        *rstn = of_get_named_gpio(spi->dev.of_node, "reset-gpio", 0);
        *slp_tr = of_get_named_gpio(spi->dev.of_node, "sleep-gpio", 0);
+       ret = of_property_read_u8(spi->dev.of_node, "xtal-trim", xtal_trim);
+       if (ret < 0 && ret != -EINVAL)
+               return ret;
 
        return 0;
 }
@@ -1505,13 +1550,14 @@ static int at86rf230_probe(struct spi_device *spi)
        struct at86rf230_local *lp;
        unsigned int status;
        int rc, irq_type, rstn, slp_tr;
+       u8 xtal_trim;
 
        if (!spi->irq) {
                dev_err(&spi->dev, "no IRQ specified\n");
                return -EINVAL;
        }
 
-       rc = at86rf230_get_pdata(spi, &rstn, &slp_tr);
+       rc = at86rf230_get_pdata(spi, &rstn, &slp_tr, &xtal_trim);
        if (rc < 0) {
                dev_err(&spi->dev, "failed to parse platform_data: %d\n", rc);
                return rc;
@@ -1570,7 +1616,7 @@ static int at86rf230_probe(struct spi_device *spi)
 
        spi_set_drvdata(spi, lp);
 
-       rc = at86rf230_hw_init(lp);
+       rc = at86rf230_hw_init(lp, xtal_trim);
        if (rc)
                goto free_dev;
 

diff --git a/include/linux/spi/at86rf230.h b/include/linux/spi/at86rf230.h
index cd519a11c2c6723d5d679ffed8cb4320eba6e318..b63fe6f5fdc874399e5125e879a071797697075d 100644 (file)
--- a/include/linux/spi/at86rf230.h
+++ b/include/linux/spi/at86rf230.h
@@ -22,6 +22,7 @@ struct at86rf230_platform_data {
        int rstn;
        int slp_tr;
        int dig2;
+       u8 xtal_trim;
 };
 
 #endif