This commit makes SmartEEE support in the AR8035 PHY optional and
configurable through the ethtool eee_set/get interface. Before this
patch, SmartEEE was always enabled except when a device tree option was
preventing it. Since EEE support not only provides advantages in power
management, but can also uncover compatibility issues and other bugs, it
is beneficial to allow users to control this functionality.

By making SmartEEE support optional and configurable via ethtool, the
at803x driver can adapt to different MAC configurations and properly
handle EEE and LPI features. This flexibility empowers users to manage
the trade-offs between power management, compatibility, and overall
performance as needed.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
---
 drivers/net/phy/at803x.c | 126 ++++++++++++++++++++++++++++++++++++---
 1 file changed, 118 insertions(+), 8 deletions(-)

diff --git a/drivers/net/phy/at803x.c b/drivers/net/phy/at803x.c
index 653d27a2e62b..4f65b3ebf806 100644
--- a/drivers/net/phy/at803x.c
+++ b/drivers/net/phy/at803x.c

@@ -165,8 +165,18 @@
 
 #define AT803X_MMD3_SMARTEEE_CTL1		0x805b
 #define AT803X_MMD3_SMARTEEE_CTL2		0x805c
+#define AT803X_MMD3_SMARTEEE_LPI_TIME_LOW	GENMASK(15, 0)
+#define AT803X_MMD3_SMARTEEE_LPI_TIME_15_0	GENMASK(15, 0)
 #define AT803X_MMD3_SMARTEEE_CTL3		0x805d
 #define AT803X_MMD3_SMARTEEE_CTL3_LPI_EN	BIT(8)
+#define AT803X_MMD3_SMARTEEE_LPI_TIME_HIGH	GENMASK(7, 0)
+#define AT803X_MMD3_SMARTEEE_LPI_TIME_23_16	GENMASK(23, 16)
+/* Tx LPI timer resolution */
+#define AT803X_MMD3_SMARTEEE_LPI_TIME_RESOL_NS	163840
+#define AT803X_MMD3_SMARTEEE_LPI_TIME_MAX_US	\
+	((GENMASK(23, 0) * AT803X_MMD3_SMARTEEE_LPI_TIME_RESOL_NS) / \
+	       NSEC_PER_USEC)
+#define AT803X_MMD3_SMARTEEE_LPI_TIME_DEF_US	335544
 
 #define ATH9331_PHY_ID				0x004dd041
 #define ATH8030_PHY_ID				0x004dd076

@@ -302,6 +312,8 @@ struct at803x_priv {
 	u8 smarteee_lpi_tw_100m;
 	bool is_fiber;
 	bool is_1000basex;
+	bool tx_lpi_on;