Documentation/networking/phy.txt

   1
   2 -------
   3 PHY Abstraction Layer
   4 (Updated 2005-07-21)
   5
   6 Purpose
   7
   8  Most network devices consist of set of registers which provide an interface
   9  to a MAC layer, which communicates with the physical connection through a
  10  PHY.  The PHY concerns itself with negotiating link parameters with the link
  11  partner on the other side of the network connection (typically, an ethernet
  12  cable), and provides a register interface to allow drivers to determine what
  13  settings were chosen, and to configure what settings are allowed.
  14
  15  While these devices are distinct from the network devices, and conform to a
  16  standard layout for the registers, it has been common practice to integrate
  17  the PHY management code with the network driver.  This has resulted in large
  18  amounts of redundant code.  Also, on embedded systems with multiple (and
  19  sometimes quite different) ethernet controllers connected to the same
  20  management bus, it is difficult to ensure safe use of the bus.
  21
  22  Since the PHYs are devices, and the management busses through which they are
  23  accessed are, in fact, busses, the PHY Abstraction Layer treats them as such.
  24  In doing so, it has these goals:
  25
  26    1) Increase code-reuse
  27    2) Increase overall code-maintainability
  28    3) Speed development time for new network drivers, and for new systems
  29
  30  Basically, this layer is meant to provide an interface to PHY devices which
  31  allows network driver writers to write as little code as possible, while
  32  still providing a full feature set.
  33
  34 The MDIO bus
  35
  36  Most network devices are connected to a PHY by means of a management bus.
  37  Different devices use different busses (though some share common interfaces).
  38  In order to take advantage of the PAL, each bus interface needs to be
  39  registered as a distinct device.
  40
  41  1) read and write functions must be implemented.  Their prototypes are:
  42
  43      int write(struct mii_bus *bus, int mii_id, int regnum, u16 value);
  44      int read(struct mii_bus *bus, int mii_id, int regnum);
  45
  46    mii_id is the address on the bus for the PHY, and regnum is the register
  47    number.  These functions are guaranteed not to be called from interrupt
  48    time, so it is safe for them to block, waiting for an interrupt to signal
  49    the operation is complete
  50
  51  2) A reset function is necessary.  This is used to return the bus to an
  52    initialized state.
  53
  54  3) A probe function is needed.  This function should set up anything the bus
  55    driver needs, setup the mii_bus structure, and register with the PAL using
  56    mdiobus_register.  Similarly, there's a remove function to undo all of
  57    that (use mdiobus_unregister).
  58
  59  4) Like any driver, the device_driver structure must be configured, and init
  60    exit functions are used to register the driver.
  61
  62  5) The bus must also be declared somewhere as a device, and registered.
  63
  64  As an example for how one driver implemented an mdio bus driver, see
  65  drivers/net/gianfar_mii.c and arch/ppc/syslib/mpc85xx_devices.c
  66
  67 Connecting to a PHY
  68
  69  Sometime during startup, the network driver needs to establish a connection
  70  between the PHY device, and the network device.  At this time, the PHY's bus
  71  and drivers need to all have been loaded, so it is ready for the connection.
  72  At this point, there are several ways to connect to the PHY:
  73
  74  1) The PAL handles everything, and only calls the network driver when
  75    the link state changes, so it can react.
  76
  77  2) The PAL handles everything except interrupts (usually because the
  78    controller has the interrupt registers).
  79
  80  3) The PAL handles everything, but checks in with the driver every second,
  81    allowing the network driver to react first to any changes before the PAL
  82    does.
  83
  84  4) The PAL serves only as a library of functions, with the network device
  85    manually calling functions to update status, and configure the PHY
  86
  87
  88 Letting the PHY Abstraction Layer do Everything
  89
  90  If you choose option 1 (The hope is that every driver can, but to still be
  91  useful to drivers that can't), connecting to the PHY is simple:
  92
  93  First, you need a function to react to changes in the link state.  This
  94  function follows this protocol:
  95
  96    static void adjust_link(struct net_device *dev);
  97
  98  Next, you need to know the device name of the PHY connected to this device.
  99  The name will look something like, "phy0:0", where the first number is the
 100  bus id, and the second is the PHY's address on that bus.
 101
 102  Now, to connect, just call this function:
 103
 104    phydev = phy_connect(dev, phy_name, &adjust_link, flags);
 105
 106  phydev is a pointer to the phy_device structure which represents the PHY.  If
 107  phy_connect is successful, it will return the pointer.  dev, here, is the
 108  pointer to your net_device.  Once done, this function will have started the
 109  PHY's software state machine, and registered for the PHY's interrupt, if it
 110  has one.  The phydev structure will be populated with information about the
 111  current state, though the PHY will not yet be truly operational at this
 112  point.
 113
 114  flags is a u32 which can optionally contain phy-specific flags.
 115  This is useful if the system has put hardware restrictions on
 116  the PHY/controller, of which the PHY needs to be aware.
 117
 118  Now just make sure that phydev->supported and phydev->advertising have any
 119  values pruned from them which don't make sense for your controller (a 10/100
 120  controller may be connected to a gigabit capable PHY, so you would need to
 121  mask off SUPPORTED_1000baseT*).  See include/linux/ethtool.h for definitions
 122  for these bitfields. Note that you should not SET any bits, or the PHY may
 123  get put into an unsupported state.
 124
 125  Lastly, once the controller is ready to handle network traffic, you call
 126  phy_start(phydev).  This tells the PAL that you are ready, and configures the
 127  PHY to connect to the network.  If you want to handle your own interrupts,
 128  just set phydev->irq to PHY_IGNORE_INTERRUPT before you call phy_start.
 129  Similarly, if you don't want to use interrupts, set phydev->irq to PHY_POLL.
 130
 131  When you want to disconnect from the network (even if just briefly), you call
 132  phy_stop(phydev).
 133
 134 Keeping Close Tabs on the PAL
 135
 136  It is possible that the PAL's built-in state machine needs a little help to
 137  keep your network device and the PHY properly in sync.  If so, you can
 138  register a helper function when connecting to the PHY, which will be called
 139  every second before the state machine reacts to any changes.  To do this, you
 140  need to manually call phy_attach() and phy_prepare_link(), and then call
 141  phy_start_machine() with the second argument set to point to your special
 142  handler.
 143
 144  Currently there are no examples of how to use this functionality, and testing
 145  on it has been limited because the author does not have any drivers which use
 146  it (they all use option 1).  So Caveat Emptor.
 147
 148 Doing it all yourself
 149
 150  There's a remote chance that the PAL's built-in state machine cannot track
 151  the complex interactions between the PHY and your network device.  If this is
 152  so, you can simply call phy_attach(), and not call phy_start_machine or
 153  phy_prepare_link().  This will mean that phydev->state is entirely yours to
 154  handle (phy_start and phy_stop toggle between some of the states, so you
 155  might need to avoid them).
 156
 157  An effort has been made to make sure that useful functionality can be
 158  accessed without the state-machine running, and most of these functions are
 159  descended from functions which did not interact with a complex state-machine.
 160  However, again, no effort has been made so far to test running without the
 161  state machine, so tryer beware.
 162
 163  Here is a brief rundown of the functions:
 164
 165  int phy_read(struct phy_device *phydev, u16 regnum);
 166  int phy_write(struct phy_device *phydev, u16 regnum, u16 val);
 167
 168    Simple read/write primitives.  They invoke the bus's read/write function
 169    pointers.
 170
 171  void phy_print_status(struct phy_device *phydev);
 172
 173    A convenience function to print out the PHY status neatly.
 174
 175  int phy_clear_interrupt(struct phy_device *phydev);
 176  int phy_config_interrupt(struct phy_device *phydev, u32 interrupts);
 177
 178    Clear the PHY's interrupt, and configure which ones are allowed,
 179    respectively.  Currently only supports all on, or all off.
 180
 181  int phy_enable_interrupts(struct phy_device *phydev);
 182  int phy_disable_interrupts(struct phy_device *phydev);
 183
 184    Functions which enable/disable PHY interrupts, clearing them
 185    before and after, respectively.
 186
 187  int phy_start_interrupts(struct phy_device *phydev);
 188  int phy_stop_interrupts(struct phy_device *phydev);
 189
 190    Requests the IRQ for the PHY interrupts, then enables them for
 191    start, or disables then frees them for stop.
 192
 193  struct phy_device * phy_attach(struct net_device *dev, const char *phy_id,
 194                  u32 flags);
 195
 196    Attaches a network device to a particular PHY, binding the PHY to a generic
 197    driver if none was found during bus initialization.  Passes in
 198    any phy-specific flags as needed.
 199
 200  int phy_start_aneg(struct phy_device *phydev);
 201
 202    Using variables inside the phydev structure, either configures advertising
 203    and resets autonegotiation, or disables autonegotiation, and configures
 204    forced settings.
 205
 206  static inline int phy_read_status(struct phy_device *phydev);
 207
 208    Fills the phydev structure with up-to-date information about the current
 209    settings in the PHY.
 210
 211  void phy_sanitize_settings(struct phy_device *phydev)
 212
 213    Resolves differences between currently desired settings, and
 214    supported settings for the given PHY device.  Does not make
 215    the changes in the hardware, though.
 216
 217  int phy_ethtool_sset(struct phy_device *phydev, struct ethtool_cmd *cmd);
 218  int phy_ethtool_gset(struct phy_device *phydev, struct ethtool_cmd *cmd);
 219
 220    Ethtool convenience functions.
 221
 222  int phy_mii_ioctl(struct phy_device *phydev,
 223                  struct mii_ioctl_data *mii_data, int cmd);
 224
 225    The MII ioctl.  Note that this function will completely screw up the state
 226    machine if you write registers like BMCR, BMSR, ADVERTISE, etc.  Best to
 227    use this only to write registers which are not standard, and don't set off
 228    a renegotiation.
 229
 230
 231 PHY Device Drivers
 232
 233  With the PHY Abstraction Layer, adding support for new PHYs is
 234  quite easy.  In some cases, no work is required at all!  However,
 235  many PHYs require a little hand-holding to get up-and-running.
 236
 237 Generic PHY driver
 238
 239  If the desired PHY doesn't have any errata, quirks, or special
 240  features you want to support, then it may be best to not add
 241  support, and let the PHY Abstraction Layer's Generic PHY Driver
 242  do all of the work.
 243
 244 Writing a PHY driver
 245
 246  If you do need to write a PHY driver, the first thing to do is
 247  make sure it can be matched with an appropriate PHY device.
 248  This is done during bus initialization by reading the device's
 249  UID (stored in registers 2 and 3), then comparing it to each
 250  driver's phy_id field by ANDing it with each driver's
 251  phy_id_mask field.  Also, it needs a name.  Here's an example:
 252
 253    static struct phy_driver dm9161_driver = {
 254          .phy_id         = 0x0181b880,
 255          .name           = "Davicom DM9161E",
 256          .phy_id_mask    = 0x0ffffff0,
 257          ...
 258    }
 259
 260  Next, you need to specify what features (speed, duplex, autoneg,
 261  etc) your PHY device and driver support.  Most PHYs support
 262  PHY_BASIC_FEATURES, but you can look in include/mii.h for other
 263  features.
 264
 265  Each driver consists of a number of function pointers:
 266
 267    config_init: configures PHY into a sane state after a reset.
 268      For instance, a Davicom PHY requires descrambling disabled.
 269    probe: Does any setup needed by the driver
 270    suspend/resume: power management
 271    config_aneg: Changes the speed/duplex/negotiation settings
 272    read_status: Reads the current speed/duplex/negotiation settings
 273    ack_interrupt: Clear a pending interrupt
 274    config_intr: Enable or disable interrupts
 275    remove: Does any driver take-down
 276
 277  Of these, only config_aneg and read_status are required to be
 278  assigned by the driver code.  The rest are optional.  Also, it is
 279  preferred to use the generic phy driver's versions of these two
 280  functions if at all possible: genphy_read_status and
 281  genphy_config_aneg.  If this is not possible, it is likely that
 282  you only need to perform some actions before and after invoking
 283  these functions, and so your functions will wrap the generic
 284  ones.
 285
 286  Feel free to look at the Marvell, Cicada, and Davicom drivers in
 287  drivers/net/phy/ for examples (the lxt and qsemi drivers have
 288  not been tested as of this writing)