phy: core: don't require set_mode() callback for phy_get_mode() to work

[ Upstream commit d58c04e ]

As reported by Damon Ding, the phy_get_mode() call doesn't work as
expected unless the PHY driver has a .set_mode() call. This prompts PHY
drivers to have empty stubs for .set_mode() for the sake of being able
to get the mode.

Make .set_mode() callback truly optional and update PHY's mode even if
it there is none.

Cc: Damon Ding <damon.ding@rock-chips.com>
Link: https://lore.kernel.org/r/96f8310f-93f1-4bcb-8637-137e1159ff83@rock-chips.com
Tested-by: Damon Ding <damon.ding@rock-chips.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20250209-phy-fix-set-moe-v2-1-76e248503856@linaro.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
(cherry picked from commit 6a7b7e98fec0aedcc413f53255359041dbc54c28)

Author: Dmitry Baryshkov

drivers/phy/phy-core.c

@@ -400,13 +400,14 @@ EXPORT_SYMBOL_GPL(phy_power_off);
 
 int phy_set_mode_ext(struct phy *phy, enum phy_mode mode, int submode)
 {
-	int ret;
+	int ret = 0;
 
-	if (!phy || !phy->ops->set_mode)
+	if (!phy)
 		return 0;
 
 	mutex_lock(&phy->mutex);
-	ret = phy->ops->set_mode(phy, mode, submode);
+	if (phy->ops->set_mode)
+		ret = phy->ops->set_mode(phy, mode, submode);
 	if (!ret)
 		phy->attrs.mode = mode;
 	mutex_unlock(&phy->mutex);