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>

3 files changed, 54 insertions, 4 deletions

diff --git a/Documentation/devicetree/bindings/net/ieee802154/at86rf230.txt b/Documentation/devicetree/bindings/net/ieee802154/at86rf230.txt
index d3bbdded4cbe..1ae5100fea14 100644
--- 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 9888b7ff24bc..c1323e5cdd0c 100644
--- 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 cd519a11c2c6..b63fe6f5fdc8 100644
--- 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