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-
--------
-PHY Abstraction Layer
-(Updated 2008-04-08)
-
-Purpose
-
- Most network devices consist of set of registers which provide an interface
- to a MAC layer, which communicates with the physical connection through a
- PHY. The PHY concerns itself with negotiating link parameters with the link
- partner on the other side of the network connection (typically, an ethernet
- cable), and provides a register interface to allow drivers to determine what
- settings were chosen, and to configure what settings are allowed.
-
- While these devices are distinct from the network devices, and conform to a
- standard layout for the registers, it has been common practice to integrate
- the PHY management code with the network driver. This has resulted in large
- amounts of redundant code. Also, on embedded systems with multiple (and
- sometimes quite different) ethernet controllers connected to the same
- management bus, it is difficult to ensure safe use of the bus.
-
- Since the PHYs are devices, and the management busses through which they are
- accessed are, in fact, busses, the PHY Abstraction Layer treats them as such.
- In doing so, it has these goals:
-
- 1) Increase code-reuse
- 2) Increase overall code-maintainability
- 3) Speed development time for new network drivers, and for new systems
-
- Basically, this layer is meant to provide an interface to PHY devices which
- allows network driver writers to write as little code as possible, while
- still providing a full feature set.
-
-The MDIO bus
-
- Most network devices are connected to a PHY by means of a management bus.
- Different devices use different busses (though some share common interfaces).
- In order to take advantage of the PAL, each bus interface needs to be
- registered as a distinct device.
-
- 1) read and write functions must be implemented. Their prototypes are:
-
- int write(struct mii_bus *bus, int mii_id, int regnum, u16 value);
- int read(struct mii_bus *bus, int mii_id, int regnum);
-
- mii_id is the address on the bus for the PHY, and regnum is the register
- number. These functions are guaranteed not to be called from interrupt
- time, so it is safe for them to block, waiting for an interrupt to signal
- the operation is complete
-
- 2) A reset function is necessary. This is used to return the bus to an
- initialized state.
-
- 3) A probe function is needed. This function should set up anything the bus
- driver needs, setup the mii_bus structure, and register with the PAL using
- mdiobus_register. Similarly, there's a remove function to undo all of
- that (use mdiobus_unregister).
-
- 4) Like any driver, the device_driver structure must be configured, and init
- exit functions are used to register the driver.
-
- 5) The bus must also be declared somewhere as a device, and registered.
-
- As an example for how one driver implemented an mdio bus driver, see
- drivers/net/ethernet/freescale/fsl_pq_mdio.c and an associated DTS file
- for one of the users. (e.g. "git grep fsl,.*-mdio arch/powerpc/boot/dts/")
-
-Connecting to a PHY
-
- Sometime during startup, the network driver needs to establish a connection
- between the PHY device, and the network device. At this time, the PHY's bus
- and drivers need to all have been loaded, so it is ready for the connection.
- At this point, there are several ways to connect to the PHY:
-
- 1) The PAL handles everything, and only calls the network driver when
- the link state changes, so it can react.
-
- 2) The PAL handles everything except interrupts (usually because the
- controller has the interrupt registers).
-
- 3) The PAL handles everything, but checks in with the driver every second,
- allowing the network driver to react first to any changes before the PAL
- does.
-
- 4) The PAL serves only as a library of functions, with the network device
- manually calling functions to update status, and configure the PHY
-
-
-Letting the PHY Abstraction Layer do Everything
-
- If you choose option 1 (The hope is that every driver can, but to still be
- useful to drivers that can't), connecting to the PHY is simple:
-
- First, you need a function to react to changes in the link state. This
- function follows this protocol:
-
- static void adjust_link(struct net_device *dev);
-
- Next, you need to know the device name of the PHY connected to this device.
- The name will look something like, "0:00", where the first number is the
- bus id, and the second is the PHY's address on that bus. Typically,
- the bus is responsible for making its ID unique.
-
- Now, to connect, just call this function:
-
- phydev = phy_connect(dev, phy_name, &adjust_link, flags, interface);
-
- phydev is a pointer to the phy_device structure which represents the PHY. If
- phy_connect is successful, it will return the pointer. dev, here, is the
- pointer to your net_device. Once done, this function will have started the
- PHY's software state machine, and registered for the PHY's interrupt, if it
- has one. The phydev structure will be populated with information about the
- current state, though the PHY will not yet be truly operational at this
- point.
-
- flags is a u32 which can optionally contain phy-specific flags.
- This is useful if the system has put hardware restrictions on
- the PHY/controller, of which the PHY needs to be aware.
-
- interface is a u32 which specifies the connection type used
- between the controller and the PHY. Examples are GMII, MII,
- RGMII, and SGMII. For a full list, see include/linux/phy.h
-
- Now just make sure that phydev->supported and phydev->advertising have any
- values pruned from them which don't make sense for your controller (a 10/100
- controller may be connected to a gigabit capable PHY, so you would need to
- mask off SUPPORTED_1000baseT*). See include/linux/ethtool.h for definitions
- for these bitfields. Note that you should not SET any bits, or the PHY may
- get put into an unsupported state.
-
- Lastly, once the controller is ready to handle network traffic, you call
- phy_start(phydev). This tells the PAL that you are ready, and configures the
- PHY to connect to the network. If you want to handle your own interrupts,
- just set phydev->irq to PHY_IGNORE_INTERRUPT before you call phy_start.
- Similarly, if you don't want to use interrupts, set phydev->irq to PHY_POLL.
-
- When you want to disconnect from the network (even if just briefly), you call
- phy_stop(phydev).
-
-Keeping Close Tabs on the PAL
-
- It is possible that the PAL's built-in state machine needs a little help to
- keep your network device and the PHY properly in sync. If so, you can
- register a helper function when connecting to the PHY, which will be called
- every second before the state machine reacts to any changes. To do this, you
- need to manually call phy_attach() and phy_prepare_link(), and then call
- phy_start_machine() with the second argument set to point to your special
- handler.
-
- Currently there are no examples of how to use this functionality, and testing
- on it has been limited because the author does not have any drivers which use
- it (they all use option 1). So Caveat Emptor.
-
-Doing it all yourself
-
- There's a remote chance that the PAL's built-in state machine cannot track
- the complex interactions between the PHY and your network device. If this is
- so, you can simply call phy_attach(), and not call phy_start_machine or
- phy_prepare_link(). This will mean that phydev->state is entirely yours to
- handle (phy_start and phy_stop toggle between some of the states, so you
- might need to avoid them).
-
- An effort has been made to make sure that useful functionality can be
- accessed without the state-machine running, and most of these functions are
- descended from functions which did not interact with a complex state-machine.
- However, again, no effort has been made so far to test running without the
- state machine, so tryer beware.
-
- Here is a brief rundown of the functions:
-
- int phy_read(struct phy_device *phydev, u16 regnum);
- int phy_write(struct phy_device *phydev, u16 regnum, u16 val);
-
- Simple read/write primitives. They invoke the bus's read/write function
- pointers.
-
- void phy_print_status(struct phy_device *phydev);
-
- A convenience function to print out the PHY status neatly.
-
- int phy_start_interrupts(struct phy_device *phydev);
- int phy_stop_interrupts(struct phy_device *phydev);
-
- Requests the IRQ for the PHY interrupts, then enables them for
- start, or disables then frees them for stop.
-
- struct phy_device * phy_attach(struct net_device *dev, const char *phy_id,
- u32 flags, phy_interface_t interface);
-
- Attaches a network device to a particular PHY, binding the PHY to a generic
- driver if none was found during bus initialization. Passes in
- any phy-specific flags as needed.
-
- int phy_start_aneg(struct phy_device *phydev);
-
- Using variables inside the phydev structure, either configures advertising
- and resets autonegotiation, or disables autonegotiation, and configures
- forced settings.
-
- static inline int phy_read_status(struct phy_device *phydev);
-
- Fills the phydev structure with up-to-date information about the current
- settings in the PHY.
-
- int phy_ethtool_sset(struct phy_device *phydev, struct ethtool_cmd *cmd);
- int phy_ethtool_gset(struct phy_device *phydev, struct ethtool_cmd *cmd);
-
- Ethtool convenience functions.
-
- int phy_mii_ioctl(struct phy_device *phydev,
- struct mii_ioctl_data *mii_data, int cmd);
-
- The MII ioctl. Note that this function will completely screw up the state
- machine if you write registers like BMCR, BMSR, ADVERTISE, etc. Best to
- use this only to write registers which are not standard, and don't set off
- a renegotiation.
-
-
-PHY Device Drivers
-
- With the PHY Abstraction Layer, adding support for new PHYs is
- quite easy. In some cases, no work is required at all! However,
- many PHYs require a little hand-holding to get up-and-running.
-
-Generic PHY driver
-
- If the desired PHY doesn't have any errata, quirks, or special
- features you want to support, then it may be best to not add
- support, and let the PHY Abstraction Layer's Generic PHY Driver
- do all of the work.
-
-Writing a PHY driver
-
- If you do need to write a PHY driver, the first thing to do is
- make sure it can be matched with an appropriate PHY device.
- This is done during bus initialization by reading the device's
- UID (stored in registers 2 and 3), then comparing it to each
- driver's phy_id field by ANDing it with each driver's
- phy_id_mask field. Also, it needs a name. Here's an example:
-
- static struct phy_driver dm9161_driver = {
- .phy_id = 0x0181b880,
- .name = "Davicom DM9161E",
- .phy_id_mask = 0x0ffffff0,
- ...
- }
-
- Next, you need to specify what features (speed, duplex, autoneg,
- etc) your PHY device and driver support. Most PHYs support
- PHY_BASIC_FEATURES, but you can look in include/mii.h for other
- features.
-
- Each driver consists of a number of function pointers:
-
- config_init: configures PHY into a sane state after a reset.
- For instance, a Davicom PHY requires descrambling disabled.
- probe: Does any setup needed by the driver
- suspend/resume: power management
- config_aneg: Changes the speed/duplex/negotiation settings
- read_status: Reads the current speed/duplex/negotiation settings
- ack_interrupt: Clear a pending interrupt
- config_intr: Enable or disable interrupts
- remove: Does any driver take-down
-
- Of these, only config_aneg and read_status are required to be
- assigned by the driver code. The rest are optional. Also, it is
- preferred to use the generic phy driver's versions of these two
- functions if at all possible: genphy_read_status and
- genphy_config_aneg. If this is not possible, it is likely that
- you only need to perform some actions before and after invoking
- these functions, and so your functions will wrap the generic
- ones.
-
- Feel free to look at the Marvell, Cicada, and Davicom drivers in
- drivers/net/phy/ for examples (the lxt and qsemi drivers have
- not been tested as of this writing)
-
-Board Fixups
-
- Sometimes the specific interaction between the platform and the PHY requires
- special handling. For instance, to change where the PHY's clock input is,
- or to add a delay to account for latency issues in the data path. In order
- to support such contingencies, the PHY Layer allows platform code to register
- fixups to be run when the PHY is brought up (or subsequently reset).
-
- When the PHY Layer brings up a PHY it checks to see if there are any fixups
- registered for it, matching based on UID (contained in the PHY device's phy_id
- field) and the bus identifier (contained in phydev->dev.bus_id). Both must
- match, however two constants, PHY_ANY_ID and PHY_ANY_UID, are provided as
- wildcards for the bus ID and UID, respectively.
-
- When a match is found, the PHY layer will invoke the run function associated
- with the fixup. This function is passed a pointer to the phy_device of
- interest. It should therefore only operate on that PHY.
-
- The platform code can either register the fixup using phy_register_fixup():
-
- int phy_register_fixup(const char *phy_id,
- u32 phy_uid, u32 phy_uid_mask,
- int (*run)(struct phy_device *));
-
- Or using one of the two stubs, phy_register_fixup_for_uid() and
- phy_register_fixup_for_id():
-
- int phy_register_fixup_for_uid(u32 phy_uid, u32 phy_uid_mask,
- int (*run)(struct phy_device *));
- int phy_register_fixup_for_id(const char *phy_id,
- int (*run)(struct phy_device *));
-
- The stubs set one of the two matching criteria, and set the other one to
- match anything.
-