title: how to retrieve bus pointer from device tree
body: <p>Question:</p>
  
  <p>I'm trying to find a way to retrieve the dev object for an <code>mdio_bus</code> that has been added to the device tree. I'm sure I'm going to be rapidly applying my palm to my forehead when I get past this, but for the life of me, I can't find the answer anywhere. I've seen how to find objects on the bus itself using <code>bus_find_device_by_name()</code>, but I can't seem to find how to get the bus itself.</p>
  
  <p>Background:</p>
  
  <p>We are providing network access to our host using a Micrel KSZ8863 Ethernet switch attached to the MACB on an at919g20. Rather than using the fixed PHY option, I've spoofed MDIO address 0 to be a "fake" PHY representing the fixed MII link to the switch. I'm writing a driver for the switch to receive its interrupts and monitor the outward facing PHYs and control the link state of the "fake" PHY to the host. In order to configure the switch beyond basic MIIM configuration, you need to use SMI on the MDIO bus to access the full array of registers in the switch. Through further tweaking of the mii_read/write functions in the MACB, adding a header to the reg address, I believe I can use the MACB's MDIO/MII controller to do the right thing for SMI requests. Because the bus no longer gets addressed by PHY:REG, I need to be able to issue raw read/write commands straight to the bus from the switch driver. And that brings me back to my question: How do I request the dev object of the <code>mdio_bus</code> from the device tree by name?</p>
  
  <p>Thanks,
  Brian</p>