drivers: eth_nxp_enet: Fix power mode control

The driver should not take the whole interface down and re-initialize on
every low power entry and exit. This is a lot of latency for no real gain
as far as I can tell. We can just do as the reference manual actually says
which is to set the sleep enable bit to put the module to sleep while still
being able to detect magic packets for wake on LAN.

Also, the only platform that this power action was "enabled" for was
kinetis, but that platform does not have any power management enabled in
Zephyr.  Which means this code was never getting called even with all the
PM configs on.  So basically this code is dead code. But it could be useful
for other platform, such as RT, so there's no reason not to remove the
dependency on kinetis and let it be used for any of the platform as long as
PM_DEVICE is enabled (hence the imply).

Signed-off-by: Declan Snyder <declan.snyder@nxp.com>

Author: decsny

drivers/ethernet/Kconfig.nxp_enet

@@ -12,7 +12,7 @@ config ETH_NXP_ENET
 	depends on DT_HAS_NXP_ENET_MAC_ENABLED
 	select NOCACHE_MEMORY if CPU_HAS_DCACHE
 	select ARM_MPU if CPU_CORTEX_M7
-	select NET_POWER_MANAGEMENT if (PM_DEVICE && SOC_FAMILY_KINETIS)
+	imply NET_POWER_MANAGEMENT
 	select ETH_DSA_SUPPORT_DEPRECATED
 	select PINCTRL
 	select HWINFO if $(dt_compat_any_has_prop,$(DT_COMPAT_NXP_ENET_MAC),$(DT_NXP_UNIQUE_MAC_PROP),True)

drivers/ethernet/eth_nxp_enet.c

@@ -799,14 +799,11 @@ static int eth_nxp_enet_device_pm_action(const struct device *dev, enum pm_devic
 			return ret;
 		}
 
-		ENET_Reset(data->base);
-		ENET_Down(data->base);
-		clock_control_off(config->clock_dev, (clock_control_subsys_t)config->clock_subsys);
+		ENET_EnableSleepMode(data->base, true);
 	} else if (action == PM_DEVICE_ACTION_RESUME) {
 		LOG_DBG("Resuming");
 
-		clock_control_on(config->clock_dev, (clock_control_subsys_t)config->clock_subsys);
-		eth_nxp_enet_init(dev);
+		ENET_EnableSleepMode(data->base, false);
 		net_if_resume(data->iface);
 	} else {
 		return -ENOTSUP;