[PATCH] ARM: mach-imx6q: add ksz9131rn_phy_fixup

[Philippe Schenker <philippe.schenker@toradex.com>]

The MAC of the i.MX6 SoC is compliant with RGMII v1.3. The KSZ9131 PHY
is like KSZ9031 adhering to RGMII v2.0 specification. This means the
MAC should provide a delay to the TXC line. Because the i.MX6 MAC does
not provide this delay this has to be done in the PHY.

This patch adds by default ~1.6ns delay to the TXC line. This should
be good for all boards that have the RGMII signals routed with the
same length.

The KSZ9131 has relatively high tolerances on skew registers from
MMD 2.4 to MMD 2.8. Therefore the new DLL-based delay of 2ns is used
and then as little as possibly subtracted from that so we get more
accurate delay. This is actually needed because the i.MX6 SoC has
an asynchron skew on TXC from -100ps to 900ps, to get all RGMII
values within spec.

Signed-off-by: Philippe Schenker <philippe.schenker@toradex.com>

---

 arch/arm/mach-imx/mach-imx6q.c | 37 ++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/arch/arm/mach-imx/mach-imx6q.c b/arch/arm/mach-imx/mach-imx6q.c
index edd26e0ffeec..8ae5f2fa33e2 100644
--- a/arch/arm/mach-imx/mach-imx6q.c
+++ b/arch/arm/mach-imx/mach-imx6q.c
@@ -61,6 +61,14 @@ static void mmd_write_reg(struct phy_device *dev, int device, int reg, int val)
 	phy_write(dev, 0x0e, val);
 }
 
+static int mmd_read_reg(struct phy_device *dev, int device, int reg)
+{
+	phy_write(dev, 0x0d, device);
+	phy_write(dev, 0x0e, reg);
+	phy_write(dev, 0x0d, (1 << 14) | device);
+	return phy_read(dev, 0x0e);
+}
+
 static int ksz9031rn_phy_fixup(struct phy_device *dev)
 {
 	/*
@@ -74,6 +82,33 @@ static int ksz9031rn_phy_fixup(struct phy_device *dev)
 	return 0;
 }
 
+#define KSZ9131_RXTXDLL_BYPASS	12
+
+static int ksz9131rn_phy_fixup(struct phy_device *dev)
+{
+	int tmp;
+
+	tmp = mmd_read_reg(dev, 2, 0x4c);
+	/* disable rxdll bypass (enable 2ns skew delay on RXC) */
+	tmp &= ~(1 << KSZ9131_RXTXDLL_BYPASS);
+	mmd_write_reg(dev, 2, 0x4c, tmp);
+
+	tmp = mmd_read_reg(dev, 2, 0x4d);
+	/* disable txdll bypass (enable 2ns skew delay on TXC) */
+	tmp &= ~(1 << KSZ9131_RXTXDLL_BYPASS);
+	mmd_write_reg(dev, 2, 0x4d, tmp);
+
+	/*
+	 * Subtract ~0.6ns from txdll = ~1.4ns delay.
+	 * leave RXC path untouched
+	 */
+	mmd_write_reg(dev, 2, 4, 0x007d);
+	mmd_write_reg(dev, 2, 6, 0xdddd);
+	mmd_write_reg(dev, 2, 8, 0x0007);
+
+	return 0;
+}
+
 /*
  * fixup for PLX PEX8909 bridge to configure GPIO1-7 as output High
  * as they are used for slots1-7 PERST#
@@ -167,6 +202,8 @@ static void __init imx6q_enet_phy_init(void)
 				ksz9021rn_phy_fixup);
 		phy_register_fixup_for_uid(PHY_ID_KSZ9031, MICREL_PHY_ID_MASK,
 				ksz9031rn_phy_fixup);
+		phy_register_fixup_for_uid(PHY_ID_KSZ9131, MICREL_PHY_ID_MASK,
+				ksz9131rn_phy_fixup);
 		phy_register_fixup_for_uid(PHY_ID_AR8031, 0xffffffef,
 				ar8031_phy_fixup);
 		phy_register_fixup_for_uid(PHY_ID_AR8035, 0xffffffef,
-- 
2.25.1