[PATCH net-next v3 5/5] net: phy: dp83867: support setting output-impedance

[Steffen Trumtrar]

Currently the dp83867 supports setting the io impedance to minimum,
maximum, default or a value from a nvmem cell. In situations where there
is no backend for a nvmem cell, the value can not be set to anything but
minimum, maximum or default.

Add support for the ti,output-impedance-ohms binding, allowing to
specify the impedance in ohms via the devicetree. The PHY has 32
settings between 35 and 70 ohms. The datasheet does not specify the
impedance of each setting, so the value is mapped linearly to the
nearest one.

With this mapping, 50 ohms results in 0x12. For non-OF devices, the
driver sets 0x0f (IO_IMPEDANCE_MIN / 2) as the 50 ohm default "per
datasheet", which would be 53 ohms with the linear mapping. As the
datasheet only gives the range, neither value can be checked against it.

The binding does not allow combining the new property with the nvmem
cell or the boolean properties. The driver still reads the nvmem cell
first, then ti,max-output-impedance, ti,min-output-impedance and
ti,output-impedance-ohms.

Signed-off-by: Steffen Trumtrar <s.trumtrar@xxxxxxxxxxxxxx>
---
 drivers/net/phy/dp83867.c | 29 +++++++++++++++++++++++++----
 1 file changed, 25 insertions(+), 4 deletions(-)

diff --git a/drivers/net/phy/dp83867.c b/drivers/net/phy/dp83867.c
index a3cd5cb11ea0..ca668e75f0c9 100644
--- a/drivers/net/phy/dp83867.c
+++ b/drivers/net/phy/dp83867.c
@@ -119,6 +119,9 @@
 #define DP83867_IO_MUX_CFG_IO_IMPEDANCE_MASK	0x1f
 #define DP83867_IO_MUX_CFG_IO_IMPEDANCE_MAX	0x0
 #define DP83867_IO_MUX_CFG_IO_IMPEDANCE_MIN	0x1f
+/* Output impedance at IO_IMPEDANCE_MIN and IO_IMPEDANCE_MAX (datasheet) */
+#define DP83867_IO_IMPEDANCE_MIN_OHMS		35
+#define DP83867_IO_IMPEDANCE_MAX_OHMS		70
 #define DP83867_IO_MUX_CFG_CLK_O_DISABLE	BIT(6)
 #define DP83867_IO_MUX_CFG_CLK_O_SEL_MASK	(0x1f << 8)
 #define DP83867_IO_MUX_CFG_CLK_O_SEL_SHIFT	8
@@ -542,7 +545,8 @@ static int dp83867_of_init_io_impedance(struct phy_device *phydev)
 	struct device *dev = &phydev->mdio.dev;
 	struct device_node *of_node = dev->of_node;
 	struct nvmem_cell *cell;
-	u8 *buf, val;
+	u8 *buf;
+	u32 val;
 	int ret;
 
 	cell = of_nvmem_cell_get(of_node, "io_impedance_ctrl");
@@ -553,12 +557,29 @@ static int dp83867_of_init_io_impedance(struct phy_device *phydev)
 						"failed to get nvmem cell io_impedance_ctrl\n");
 
 		/* If no nvmem cell, check for the boolean properties. */
-		if (of_property_read_bool(of_node, "ti,max-output-impedance"))
+		if (of_property_read_bool(of_node, "ti,max-output-impedance")) {
 			dp83867->io_impedance = DP83867_IO_MUX_CFG_IO_IMPEDANCE_MAX;
-		else if (of_property_read_bool(of_node, "ti,min-output-impedance"))
+		} else if (of_property_read_bool(of_node, "ti,min-output-impedance")) {
 			dp83867->io_impedance = DP83867_IO_MUX_CFG_IO_IMPEDANCE_MIN;
-		else
+		} else if (of_property_read_u32(of_node, "ti,output-impedance-ohms", &val) == 0) {
+			if (val < DP83867_IO_IMPEDANCE_MIN_OHMS ||
+			    val > DP83867_IO_IMPEDANCE_MAX_OHMS) {
+				phydev_err(phydev, "'ti,output-impedance-ohms' contents out of range\n");
+				return -ERANGE;
+			}
+			/*
+			 * 0x00 = 70 ohms ... 0x1f = 35 ohms. The datasheet
+			 * does not specify the settings in between, map the
+			 * range linearly to the nearest one.
+			 */
+			dp83867->io_impedance =
+				DIV_ROUND_CLOSEST((DP83867_IO_IMPEDANCE_MAX_OHMS - val) *
+						  DP83867_IO_MUX_CFG_IO_IMPEDANCE_MASK,
+						  DP83867_IO_IMPEDANCE_MAX_OHMS -
+						  DP83867_IO_IMPEDANCE_MIN_OHMS);
+		} else {
 			dp83867->io_impedance = -1; /* leave at default */
+		}
 
 		return 0;
 	}

-- 
2.56.0