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Diffstat (limited to 'kernel/Documentation/networking/phy.txt')
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diff --git a/kernel/Documentation/networking/phy.txt b/kernel/Documentation/networking/phy.txt new file mode 100644 index 000000000..e839e7efc --- /dev/null +++ b/kernel/Documentation/networking/phy.txt @@ -0,0 +1,339 @@ + +------- +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 optional. 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, 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. + + PHY-specific flags should be set in phydev->dev_flags prior to the call + to phy_connect() such that the underlying PHY driver can check for flags + and perform specific operations based on them. + 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, + 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. + + 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: + + soft_reset: perform a PHY software reset + config_init: configures PHY into a sane state after a reset. + For instance, a Davicom PHY requires descrambling disabled. + probe: Allocate phy->priv, optionally refuse to bind. + PHY may not have been reset or had fixups run yet. + suspend/resume: power management + config_aneg: Changes the speed/duplex/negotiation settings + aneg_done: Determines the auto-negotiation result + read_status: Reads the current speed/duplex/negotiation settings + ack_interrupt: Clear a pending interrupt + did_interrupt: Checks if the PHY generated an interrupt + config_intr: Enable or disable interrupts + remove: Does any driver take-down + ts_info: Queries about the HW timestamping status + hwtstamp: Set the PHY HW timestamping configuration + rxtstamp: Requests a receive timestamp at the PHY level for a 'skb' + txtsamp: Requests a transmit timestamp at the PHY level for a 'skb' + set_wol: Enable Wake-on-LAN at the PHY level + get_wol: Get the Wake-on-LAN status at the PHY level + read_mmd_indirect: Read PHY MMD indirect register + write_mmd_indirect: Write PHY MMD indirect register + + 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). + + The PHY's MMD register accesses are handled by the PAL framework + by default, but can be overridden by a specific PHY driver if + required. This could be the case if a PHY was released for + manufacturing before the MMD PHY register definitions were + standardized by the IEEE. Most modern PHYs will be able to use + the generic PAL framework for accessing the PHY's MMD registers. + An example of such usage is for Energy Efficient Ethernet support, + implemented in the PAL. This support uses the PAL to access MMD + registers for EEE query and configuration if the PHY supports + the IEEE standard access mechanisms, or can use the PHY's specific + access interfaces if overridden by the specific PHY driver. See + the Micrel driver in drivers/net/phy/ for an example of how this + can be implemented. + +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. + |