netdev - Need help with mdiobus

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Date:   Thu, 13 Oct 2016 18:15:39 -0500
From:   Timur Tabi <timur@...eaurora.org>
To:     netdev@...r.kernel.org
Subject: Need help with mdiobus_register and phy

I need help with a program I've discovered with my driver 
(ethernet/qualcomm/emac/) that occurs in the following process:

1. Load the driver
1a. Driver calls mdiobus_register (see emac_phy_config), which calls 
mdiobus_scan(), which calls get_phy_device()
1b. get_phy_device() performs MDIO bus operations, which means the bus 
and the external phy need to be active.
2. Bring up the interface
3. Bring down the interface.  This calls phy_disconnect() which calls 
phy_detach() which calls phy_suspend().  This puts the external phy to 
sleep.
4. Unload the driver
5. Re-load the driver.
5a. Driver calls mdiobus_register again, but this time the call to 
get_phy_device() fails because the external phy is asleep and does not 
respond to MDIO transactions.

I don't know what my driver is doing wrong.  I'm concerned that 
mdiobus_register() is causing MDIO transactions to occur before the rest 
of the EMAC has a chance to initialize.  I've examined many other 
drivers, and I think I'm initializing things in the proper order.

The call to mdiobus_register() occurs before I know what phydev is. 
Since I need the phydev in order to talk to the phy driver, I don't see 
how I can "wake up" the external phy before calling mdiobus_register().

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