[PATCH AUTOSEL 4.14 15/46] net: phy: Add general dummy stubs for MMD register access

[Sasha Levin <sashal@kernel.org>]

From: Kevin Hao <haokexin@gmail.com>

[ Upstream commit 5df7af85ecd88e8b5f1f31d6456c3cf38a8bbdda ]

For some phy devices, even though they don't support the MMD extended
register access, it does have some side effect if we are trying to
read/write the MMD registers via indirect method. So introduce general
dummy stubs for MMD register access which these devices can use to avoid
such side effect.

Fixes: b6b5e8a69118 ("gianfar: Disable EEE autoneg by default")
Signed-off-by: Kevin Hao <haokexin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/net/phy/phy_device.c | 17 +++++++++++++++++
 include/linux/phy.h          |  4 ++++
 2 files changed, 21 insertions(+)

diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index a174d05a9752..fe76e2c4022a 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -1641,6 +1641,23 @@ int genphy_config_init(struct phy_device *phydev)
 }
 EXPORT_SYMBOL(genphy_config_init);
 
+/* This is used for the phy device which doesn't support the MMD extended
+ * register access, but it does have side effect when we are trying to access
+ * the MMD register via indirect method.
+ */
+int genphy_read_mmd_unsupported(struct phy_device *phdev, int devad, u16 regnum)
+{
+	return -EOPNOTSUPP;
+}
+EXPORT_SYMBOL(genphy_read_mmd_unsupported);
+
+int genphy_write_mmd_unsupported(struct phy_device *phdev, int devnum,
+				 u16 regnum, u16 val)
+{
+	return -EOPNOTSUPP;
+}
+EXPORT_SYMBOL(genphy_write_mmd_unsupported);
+
 int genphy_suspend(struct phy_device *phydev)
 {
 	int value;
diff --git a/include/linux/phy.h b/include/linux/phy.h
index dca9e926b88f..efc04c2d92c9 100644
--- a/include/linux/phy.h
+++ b/include/linux/phy.h
@@ -879,6 +879,10 @@ static inline int genphy_no_soft_reset(struct phy_device *phydev)
 {
 	return 0;
 }
+int genphy_read_mmd_unsupported(struct phy_device *phdev, int devad,
+				u16 regnum);
+int genphy_write_mmd_unsupported(struct phy_device *phdev, int devnum,
+				 u16 regnum, u16 val);
 
 /* Clause 45 PHY */
 int genphy_c45_restart_aneg(struct phy_device *phydev);
-- 
2.17.1