[PATCH v2 2/4] net: phy: ksz90x1: Handle ksz9131 LED errata

[Paul Barker]

Micrel KSZ9131 PHY LED behavior is not correct when configured in
Individual Mode, LED1 (Activity LED) is in the ON state when there is
no-link.

Workaround this by setting bit 9 of register 0x1e after verifying that
the LED configuration is Individual Mode.

This issue is described in KSZ9131RNX Silicon Errata DS80000693B [*]
and according to that it will not be corrected in a future silicon
revision.

[*] https://ww1.microchip.com/downloads/en/DeviceDoc/KSZ9131RNX-Silicon-Errata-and-Data-Sheet-Clarification-80000863B.pdf

Based on commit 0316c7e66bbd in the Linux kernel.

Signed-off-by: Paul Barker <paul.barker.ct at bp.renesas.com>
---
Changes v1->v2:
  - Split out of series adding RZ/G2L Ethernet support [1]
  - Add symbols KSZ9131RN_COMMON_CTRL, KSZ9131RN_COMMON_CTRL_LED_MODE,
    KSZ9131RN_LED_ERRATA_REG, KSZ9131RN_LED_ERRATA_BITS

[1]: https://lore.kernel.org/all/20241024152448.102-1-paul.barker.ct@bp.renesas.com/

 drivers/net/phy/micrel_ksz90x1.c | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/drivers/net/phy/micrel_ksz90x1.c b/drivers/net/phy/micrel_ksz90x1.c
index c48ae6e88f30..b33457910795 100644
--- a/drivers/net/phy/micrel_ksz90x1.c
+++ b/drivers/net/phy/micrel_ksz90x1.c
@@ -389,6 +389,12 @@ U_BOOT_PHY_DRIVER(ksz9031) = {
 #define KSZ9131RN_DLL_ENABLE_DELAY	0
 #define KSZ9131RN_DLL_DISABLE_DELAY	BIT(12)
 
+#define KSZ9131RN_COMMON_CTRL		0
+#define KSZ9131RN_COMMON_CTRL_LED_MODE	BIT(4)
+
+#define KSZ9131RN_LED_ERRATA_REG	0x1e
+#define KSZ9131RN_LED_ERRATA_BITS	BIT(9)
+
 static int ksz9131_config_rgmii_delay(struct phy_device *phydev)
 {
 	struct phy_driver *drv = phydev->drv;
@@ -436,6 +442,28 @@ static int ksz9131_config_rgmii_delay(struct phy_device *phydev)
 	return ret;
 }
 
+/* Silicon Errata DS80000693B
+ *
+ * When LEDs are configured in Individual Mode, LED1 is ON in a no-link
+ * condition. Workaround is to set register 0x1e, bit 9, this way LED1 behaves
+ * according to the datasheet (off if there is no link).
+ */
+static int ksz9131_led_errata(struct phy_device *phydev)
+{
+	int reg;
+
+	reg = phy_read_mmd(phydev, KSZ9131RN_MMD_COMMON_CTRL_REG,
+			   KSZ9131RN_COMMON_CTRL);
+	if (reg < 0)
+		return reg;
+
+	if (!(reg & KSZ9131RN_COMMON_CTRL_LED_MODE))
+		return 0;
+
+	return phy_set_bits(phydev, MDIO_DEVAD_NONE, KSZ9131RN_LED_ERRATA_REG,
+			    KSZ9131RN_LED_ERRATA_BITS);
+}
+
 static int ksz9131_config(struct phy_device *phydev)
 {
 	int ret;
@@ -446,6 +474,10 @@ static int ksz9131_config(struct phy_device *phydev)
 			return ret;
 	}
 
+	ret = ksz9131_led_errata(phydev);
+	if (ret < 0)
+		return ret;
+
 	/* add an option to disable the gigabit feature of this PHY */
 	if (env_get("disable_giga")) {
 		unsigned features;
-- 
2.43.0