This patch adds a PHY Abstraction Layer to the Linux Kernel, enabling

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PHY Abstraction Layer

(Updated 2005-07-21)

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/gianfar_mii.c and arch/ppc/syslib/mpc85xx_devices.c

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, "phy0:0", where the first number is the

 bus id, and the second is the PHY's address on that bus.

 Now, to connect, just call this function:

   phydev = phy_connect(dev, phy_name, &adjust_link, flags);

 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.

 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_clear_interrupt(struct phy_device *phydev);

 int phy_config_interrupt(struct phy_device *phydev, u32 interrupts);

   Clear the PHY's interrupt, and configure which ones are allowed,

   respectively.  Currently only supports all on, or all off.

 int phy_enable_interrupts(struct phy_device *phydev);

 int phy_disable_interrupts(struct phy_device *phydev);

   Functions which enable/disable PHY interrupts, clearing them

   before and after, respectively.

 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);

   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.

 void phy_sanitize_settings(struct phy_device *phydev)

   Resolves differences between currently desired settings, and

   supported settings for the given PHY device.  Does not make

   the changes in the hardware, though.

 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)

	source "drivers/net/arcnet/Kconfig"

source "drivers/net/phy/Kconfig"

#

#	Ethernet

#

#

obj-$(CONFIG_MII) += mii.o

obj-$(CONFIG_PHYLIB) += phy/

obj-$(CONFIG_SUNDANCE) += sundance.o

obj-$(CONFIG_HAMACHI) += hamachi.o

#

# PHY Layer Configuration

#

menu "PHY device support"

config PHYLIB

	bool "PHY Device support and infrastructure"

	depends on NET_ETHERNET

	help

	  Ethernet controllers are usually attached to PHY

	  devices.  This option provides infrastructure for

	  managing PHY devices.

config PHYCONTROL

	bool "Support for automatically handling PHY state changes"

	depends on PHYLIB

	help

	  Adds code to perform all the work for keeping PHY link

	  state (speed/duplex/etc) up-to-date.  Also handles

	  interrupts.

comment "MII PHY device drivers"

	depends on PHYLIB

config MARVELL_PHY

	bool "Drivers for Marvell PHYs"

	depends on PHYLIB

	---help---

	  Currently has a driver for the 88E1011S

config DAVICOM_PHY

	bool "Drivers for Davicom PHYs"

	depends on PHYLIB

	---help---

	  Currently supports dm9161e and dm9131

config QSEMI_PHY

	bool "Drivers for Quality Semiconductor PHYs"

	depends on PHYLIB

	---help---

	  Currently supports the qs6612

config LXT_PHY

	bool "Drivers for the Intel LXT PHYs"

	depends on PHYLIB

	---help---

	  Currently supports the lxt970, lxt971

config CICADA_PHY

	bool "Drivers for the Cicada PHYs"

	depends on PHYLIB

	---help---

	  Currently supports the cis8204

endmenu

# Makefile for Linux PHY drivers

obj-$(CONFIG_PHYLIB) += phy.o phy_device.o mdio_bus.o

obj-$(CONFIG_MARVELL_PHY) += marvell.o

obj-$(CONFIG_DAVICOM_PHY) += davicom.o

obj-$(CONFIG_CICADA_PHY) += cicada.o

obj-$(CONFIG_LXT_PHY) += lxt.o

obj-$(CONFIG_QSEMI_PHY) += qsemi.o