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Based on kernel version 3.16. Page generated on 2014-08-06 21:40 EST.

1	
2	-------
3	PHY Abstraction Layer
4	(Updated 2008-04-08)
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 optional.  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/ethernet/freescale/fsl_pq_mdio.c and an associated DTS file
66	 for one of the users. (e.g. "git grep fsl,.*-mdio arch/powerpc/boot/dts/")
67	
68	Connecting to a PHY
69	
70	 Sometime during startup, the network driver needs to establish a connection
71	 between the PHY device, and the network device.  At this time, the PHY's bus
72	 and drivers need to all have been loaded, so it is ready for the connection.
73	 At this point, there are several ways to connect to the PHY:
74	
75	 1) The PAL handles everything, and only calls the network driver when
76	   the link state changes, so it can react.
77	
78	 2) The PAL handles everything except interrupts (usually because the
79	   controller has the interrupt registers).
80	
81	 3) The PAL handles everything, but checks in with the driver every second,
82	   allowing the network driver to react first to any changes before the PAL
83	   does.
84	 
85	 4) The PAL serves only as a library of functions, with the network device
86	   manually calling functions to update status, and configure the PHY
87	
88	
89	Letting the PHY Abstraction Layer do Everything
90	
91	 If you choose option 1 (The hope is that every driver can, but to still be
92	 useful to drivers that can't), connecting to the PHY is simple:
93	
94	 First, you need a function to react to changes in the link state.  This
95	 function follows this protocol:
96	
97	   static void adjust_link(struct net_device *dev);
98	 
99	 Next, you need to know the device name of the PHY connected to this device. 
100	 The name will look something like, "0:00", where the first number is the
101	 bus id, and the second is the PHY's address on that bus.  Typically,
102	 the bus is responsible for making its ID unique.
103	 
104	 Now, to connect, just call this function:
105	 
106	   phydev = phy_connect(dev, phy_name, &adjust_link, interface);
107	
108	 phydev is a pointer to the phy_device structure which represents the PHY.  If
109	 phy_connect is successful, it will return the pointer.  dev, here, is the
110	 pointer to your net_device.  Once done, this function will have started the
111	 PHY's software state machine, and registered for the PHY's interrupt, if it
112	 has one.  The phydev structure will be populated with information about the
113	 current state, though the PHY will not yet be truly operational at this
114	 point.
115	
116	 PHY-specific flags should be set in phydev->dev_flags prior to the call
117	 to phy_connect() such that the underlying PHY driver can check for flags
118	 and perform specific operations based on them.
119	 This is useful if the system has put hardware restrictions on
120	 the PHY/controller, of which the PHY needs to be aware.
121	
122	 interface is a u32 which specifies the connection type used
123	 between the controller and the PHY.  Examples are GMII, MII,
124	 RGMII, and SGMII.  For a full list, see include/linux/phy.h
125	
126	 Now just make sure that phydev->supported and phydev->advertising have any
127	 values pruned from them which don't make sense for your controller (a 10/100
128	 controller may be connected to a gigabit capable PHY, so you would need to
129	 mask off SUPPORTED_1000baseT*).  See include/linux/ethtool.h for definitions
130	 for these bitfields. Note that you should not SET any bits, or the PHY may
131	 get put into an unsupported state.
132	
133	 Lastly, once the controller is ready to handle network traffic, you call
134	 phy_start(phydev).  This tells the PAL that you are ready, and configures the
135	 PHY to connect to the network.  If you want to handle your own interrupts,
136	 just set phydev->irq to PHY_IGNORE_INTERRUPT before you call phy_start.
137	 Similarly, if you don't want to use interrupts, set phydev->irq to PHY_POLL.
138	
139	 When you want to disconnect from the network (even if just briefly), you call
140	 phy_stop(phydev).
141	
142	Keeping Close Tabs on the PAL
143	
144	 It is possible that the PAL's built-in state machine needs a little help to
145	 keep your network device and the PHY properly in sync.  If so, you can
146	 register a helper function when connecting to the PHY, which will be called
147	 every second before the state machine reacts to any changes.  To do this, you
148	 need to manually call phy_attach() and phy_prepare_link(), and then call
149	 phy_start_machine() with the second argument set to point to your special
150	 handler.
151	
152	 Currently there are no examples of how to use this functionality, and testing
153	 on it has been limited because the author does not have any drivers which use
154	 it (they all use option 1).  So Caveat Emptor.
155	
156	Doing it all yourself
157	
158	 There's a remote chance that the PAL's built-in state machine cannot track
159	 the complex interactions between the PHY and your network device.  If this is
160	 so, you can simply call phy_attach(), and not call phy_start_machine or
161	 phy_prepare_link().  This will mean that phydev->state is entirely yours to
162	 handle (phy_start and phy_stop toggle between some of the states, so you
163	 might need to avoid them).
164	
165	 An effort has been made to make sure that useful functionality can be
166	 accessed without the state-machine running, and most of these functions are
167	 descended from functions which did not interact with a complex state-machine.
168	 However, again, no effort has been made so far to test running without the
169	 state machine, so tryer beware.
170	
171	 Here is a brief rundown of the functions:
172	
173	 int phy_read(struct phy_device *phydev, u16 regnum);
174	 int phy_write(struct phy_device *phydev, u16 regnum, u16 val);
175	
176	   Simple read/write primitives.  They invoke the bus's read/write function
177	   pointers.
178	
179	 void phy_print_status(struct phy_device *phydev);
180	 
181	   A convenience function to print out the PHY status neatly.
182	
183	 int phy_start_interrupts(struct phy_device *phydev);
184	 int phy_stop_interrupts(struct phy_device *phydev);
185	
186	   Requests the IRQ for the PHY interrupts, then enables them for
187	   start, or disables then frees them for stop.
188	
189	 struct phy_device * phy_attach(struct net_device *dev, const char *phy_id,
190			 phy_interface_t interface);
191	
192	   Attaches a network device to a particular PHY, binding the PHY to a generic
193	   driver if none was found during bus initialization.
194	
195	 int phy_start_aneg(struct phy_device *phydev);
196	   
197	   Using variables inside the phydev structure, either configures advertising
198	   and resets autonegotiation, or disables autonegotiation, and configures
199	   forced settings.
200	
201	 static inline int phy_read_status(struct phy_device *phydev);
202	
203	   Fills the phydev structure with up-to-date information about the current
204	   settings in the PHY.
205	
206	 int phy_ethtool_sset(struct phy_device *phydev, struct ethtool_cmd *cmd);
207	 int phy_ethtool_gset(struct phy_device *phydev, struct ethtool_cmd *cmd);
208	
209	   Ethtool convenience functions.
210	
211	 int phy_mii_ioctl(struct phy_device *phydev,
212	                 struct mii_ioctl_data *mii_data, int cmd);
213	
214	   The MII ioctl.  Note that this function will completely screw up the state
215	   machine if you write registers like BMCR, BMSR, ADVERTISE, etc.  Best to
216	   use this only to write registers which are not standard, and don't set off
217	   a renegotiation.
218	
219	
220	PHY Device Drivers
221	
222	 With the PHY Abstraction Layer, adding support for new PHYs is
223	 quite easy.  In some cases, no work is required at all!  However,
224	 many PHYs require a little hand-holding to get up-and-running.
225	
226	Generic PHY driver
227	
228	 If the desired PHY doesn't have any errata, quirks, or special
229	 features you want to support, then it may be best to not add
230	 support, and let the PHY Abstraction Layer's Generic PHY Driver
231	 do all of the work.  
232	
233	Writing a PHY driver
234	
235	 If you do need to write a PHY driver, the first thing to do is
236	 make sure it can be matched with an appropriate PHY device.
237	 This is done during bus initialization by reading the device's
238	 UID (stored in registers 2 and 3), then comparing it to each
239	 driver's phy_id field by ANDing it with each driver's
240	 phy_id_mask field.  Also, it needs a name.  Here's an example:
241	
242	   static struct phy_driver dm9161_driver = {
243	         .phy_id         = 0x0181b880,
244		 .name           = "Davicom DM9161E",
245		 .phy_id_mask    = 0x0ffffff0,
246		 ...
247	   }
248	
249	 Next, you need to specify what features (speed, duplex, autoneg,
250	 etc) your PHY device and driver support.  Most PHYs support
251	 PHY_BASIC_FEATURES, but you can look in include/mii.h for other
252	 features.
253	
254	 Each driver consists of a number of function pointers:
255	
256	   soft_reset: perform a PHY software reset
257	   config_init: configures PHY into a sane state after a reset.
258	     For instance, a Davicom PHY requires descrambling disabled.
259	   probe: Allocate phy->priv, optionally refuse to bind.
260	   PHY may not have been reset or had fixups run yet.
261	   suspend/resume: power management
262	   config_aneg: Changes the speed/duplex/negotiation settings
263	   aneg_done: Determines the auto-negotiation result
264	   read_status: Reads the current speed/duplex/negotiation settings
265	   ack_interrupt: Clear a pending interrupt
266	   did_interrupt: Checks if the PHY generated an interrupt
267	   config_intr: Enable or disable interrupts
268	   remove: Does any driver take-down
269	   ts_info: Queries about the HW timestamping status
270	   hwtstamp: Set the PHY HW timestamping configuration
271	   rxtstamp: Requests a receive timestamp at the PHY level for a 'skb'
272	   txtsamp: Requests a transmit timestamp at the PHY level for a 'skb'
273	   set_wol: Enable Wake-on-LAN at the PHY level
274	   get_wol: Get the Wake-on-LAN status at the PHY level
275	
276	 Of these, only config_aneg and read_status are required to be
277	 assigned by the driver code.  The rest are optional.  Also, it is
278	 preferred to use the generic phy driver's versions of these two
279	 functions if at all possible: genphy_read_status and
280	 genphy_config_aneg.  If this is not possible, it is likely that
281	 you only need to perform some actions before and after invoking
282	 these functions, and so your functions will wrap the generic
283	 ones.
284	
285	 Feel free to look at the Marvell, Cicada, and Davicom drivers in
286	 drivers/net/phy/ for examples (the lxt and qsemi drivers have
287	 not been tested as of this writing)
288	
289	Board Fixups
290	
291	 Sometimes the specific interaction between the platform and the PHY requires
292	 special handling.  For instance, to change where the PHY's clock input is,
293	 or to add a delay to account for latency issues in the data path.  In order
294	 to support such contingencies, the PHY Layer allows platform code to register
295	 fixups to be run when the PHY is brought up (or subsequently reset).
296	
297	 When the PHY Layer brings up a PHY it checks to see if there are any fixups
298	 registered for it, matching based on UID (contained in the PHY device's phy_id
299	 field) and the bus identifier (contained in phydev->dev.bus_id).  Both must
300	 match, however two constants, PHY_ANY_ID and PHY_ANY_UID, are provided as
301	 wildcards for the bus ID and UID, respectively.
302	
303	 When a match is found, the PHY layer will invoke the run function associated
304	 with the fixup.  This function is passed a pointer to the phy_device of
305	 interest.  It should therefore only operate on that PHY.
306	
307	 The platform code can either register the fixup using phy_register_fixup():
308	
309		int phy_register_fixup(const char *phy_id,
310			u32 phy_uid, u32 phy_uid_mask,
311			int (*run)(struct phy_device *));
312	
313	 Or using one of the two stubs, phy_register_fixup_for_uid() and
314	 phy_register_fixup_for_id():
315	
316	 int phy_register_fixup_for_uid(u32 phy_uid, u32 phy_uid_mask,
317			int (*run)(struct phy_device *));
318	 int phy_register_fixup_for_id(const char *phy_id,
319			int (*run)(struct phy_device *));
320	
321	 The stubs set one of the two matching criteria, and set the other one to
322	 match anything.
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