net: phy: dp83867: Add ability to disable output clock

Generally, the output clock pin is only used for testing and only serves
as a source of RF noise after this.  It could be used to daisy-chain
PHYs, but this is uncommon.  Since the PHY can disable the output, make
doing so an option.  I do this by adding another enumeration to the
allowed values of ti,clk-output-sel.

The code was not using the value DP83867_CLK_O_SEL_REF_CLK as one might
expect: to select the REF_CLK as the output.  Rather it meant "keep
clock output setting as is", which, depending on PHY strapping, might
not be outputting REF_CLK.

Change this so DP83867_CLK_O_SEL_REF_CLK means enable REF_CLK output.
Omitting the property will leave the setting as is (which was the
previous behavior in this case).

Out of range values were silently converted into
DP83867_CLK_O_SEL_REF_CLK.  Change this so they generate an error.

Cc: Andrew Lunn <andrew@lunn.ch>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Trent Piepho <tpiepho@impinj.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/dp83867.c

@@ -68,6 +68,7 @@
 
 #define DP83867_IO_MUX_CFG_IO_IMPEDANCE_MAX	0x0
 #define DP83867_IO_MUX_CFG_IO_IMPEDANCE_MIN	0x1f
+#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
 
@@ -87,7 +88,8 @@ struct dp83867_private {
 	int io_impedance;
 	int port_mirroring;
 	bool rxctrl_strap_quirk;
-	int clk_output_sel;
+	bool set_clk_output;
+	u32 clk_output_sel;
 };
 
 static int dp83867_ack_interrupt(struct phy_device *phydev)
@@ -154,11 +156,19 @@ static int dp83867_of_init(struct phy_device *phydev)
 	/* Optional configuration */
 	ret = of_property_read_u32(of_node, "ti,clk-output-sel",
 				   &dp83867->clk_output_sel);
-	if (ret || dp83867->clk_output_sel > DP83867_CLK_O_SEL_REF_CLK)
-		/* Keep the default value if ti,clk-output-sel is not set
-		 * or too high
+	/* If not set, keep default */
+	if (!ret) {
+		dp83867->set_clk_output = true;
+		/* Valid values are 0 to DP83867_CLK_O_SEL_REF_CLK or
+		 * DP83867_CLK_O_SEL_OFF.
 		 */
-		dp83867->clk_output_sel = DP83867_CLK_O_SEL_REF_CLK;
+		if (dp83867->clk_output_sel > DP83867_CLK_O_SEL_REF_CLK &&
+		    dp83867->clk_output_sel != DP83867_CLK_O_SEL_OFF) {
+			phydev_err(phydev, "ti,clk-output-sel value %u out of range\n",
+				   dp83867->clk_output_sel);
+			return -EINVAL;
+		}
+	}
 
 	if (of_property_read_bool(of_node, "ti,max-output-impedance"))
 		dp83867->io_impedance = DP83867_IO_MUX_CFG_IO_IMPEDANCE_MAX;
@@ -288,11 +298,20 @@ static int dp83867_config_init(struct phy_device *phydev)
 		dp83867_config_port_mirroring(phydev);
 
 	/* Clock output selection if muxing property is set */
-	if (dp83867->clk_output_sel != DP83867_CLK_O_SEL_REF_CLK)
+	if (dp83867->set_clk_output) {
+		u16 mask = DP83867_IO_MUX_CFG_CLK_O_DISABLE;
+
+		if (dp83867->clk_output_sel == DP83867_CLK_O_SEL_OFF) {
+			val = DP83867_IO_MUX_CFG_CLK_O_DISABLE;
+		} else {
+			mask |= DP83867_IO_MUX_CFG_CLK_O_SEL_MASK;
+			val = dp83867->clk_output_sel <<
+			      DP83867_IO_MUX_CFG_CLK_O_SEL_SHIFT;
+		}
+
 		phy_modify_mmd(phydev, DP83867_DEVADDR, DP83867_IO_MUX_CFG,
-			       DP83867_IO_MUX_CFG_CLK_O_SEL_MASK,
-			       dp83867->clk_output_sel <<
-			       DP83867_IO_MUX_CFG_CLK_O_SEL_SHIFT);
+			       mask, val);
+	}
 
 	return 0;
 }