Adding upstream version 4.19.249.upstream/4.19.249

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 427 insertions, 0 deletions

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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 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/")
+
+(RG)MII/electrical interface considerations
+
+ The Reduced Gigabit Medium Independent Interface (RGMII) is a 12-pin
+ electrical signal interface using a synchronous 125Mhz clock signal and several
+ data lines. Due to this design decision, a 1.5ns to 2ns delay must be added
+ between the clock line (RXC or TXC) and the data lines to let the PHY (clock
+ sink) have enough setup and hold times to sample the data lines correctly. The
+ PHY library offers different types of PHY_INTERFACE_MODE_RGMII* values to let
+ the PHY driver and optionally the MAC driver, implement the required delay. The
+ values of phy_interface_t must be understood from the perspective of the PHY
+ device itself, leading to the following:
+
+ * PHY_INTERFACE_MODE_RGMII: the PHY is not responsible for inserting any
+   internal delay by itself, it assumes that either the Ethernet MAC (if capable
+   or the PCB traces) insert the correct 1.5-2ns delay
+
+ * PHY_INTERFACE_MODE_RGMII_TXID: the PHY should insert an internal delay
+   for the transmit data lines (TXD[3:0]) processed by the PHY device
+
+ * PHY_INTERFACE_MODE_RGMII_RXID: the PHY should insert an internal delay
+   for the receive data lines (RXD[3:0]) processed by the PHY device
+
+ * PHY_INTERFACE_MODE_RGMII_ID: the PHY should insert internal delays for
+   both transmit AND receive data lines from/to the PHY device
+
+ Whenever possible, use the PHY side RGMII delay for these reasons:
+
+ * PHY devices may offer sub-nanosecond granularity in how they allow a
+   receiver/transmitter side delay (e.g: 0.5, 1.0, 1.5ns) to be specified. Such
+   precision may be required to account for differences in PCB trace lengths
+
+ * PHY devices are typically qualified for a large range of applications
+   (industrial, medical, automotive...), and they provide a constant and
+   reliable delay across temperature/pressure/voltage ranges
+
+ * PHY device drivers in PHYLIB being reusable by nature, being able to
+   configure correctly a specified delay enables more designs with similar delay
+   requirements to be operate correctly
+
+ For cases where the PHY is not capable of providing this delay, but the
+ Ethernet MAC driver is capable of doing so, the correct phy_interface_t value
+ should be PHY_INTERFACE_MODE_RGMII, and the Ethernet MAC driver should be
+ configured correctly in order to provide the required transmit and/or receive
+ side delay from the perspective of the PHY device. Conversely, if the Ethernet
+ MAC driver looks at the phy_interface_t value, for any other mode but
+ PHY_INTERFACE_MODE_RGMII, it should make sure that the MAC-level delays are
+ disabled.
+
+ In case neither the Ethernet MAC, nor the PHY are capable of providing the
+ required delays, as defined per the RGMII standard, several options may be
+ available:
+
+ * Some SoCs may offer a pin pad/mux/controller capable of configuring a given
+   set of pins'strength, delays, and voltage; and it may be a suitable
+   option to insert the expected 2ns RGMII delay.
+
+ * Modifying the PCB design to include a fixed delay (e.g: using a specifically
+   designed serpentine), which may not require software configuration at all.
+
+Common problems with RGMII delay mismatch
+
+ When there is a RGMII delay mismatch between the Ethernet MAC and the PHY, this
+ will most likely result in the clock and data line signals to be unstable when
+ the PHY or MAC take a snapshot of these signals to translate them into logical
+ 1 or 0 states and reconstruct the data being transmitted/received. Typical
+ symptoms include:
+
+ * Transmission/reception partially works, and there is frequent or occasional
+   packet loss observed
+
+ * Ethernet MAC may report some or all packets ingressing with a FCS/CRC error,
+   or just discard them all
+
+ * Switching to lower speeds such as 10/100Mbits/sec makes the problem go away
+   (since there is enough setup/hold time in that case)
+
+
+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, except the
+ SUPPORTED_Pause and SUPPORTED_AsymPause bits (see below), 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).
+
+Pause frames / flow control
+
+ The PHY does not participate directly in flow control/pause frames except by
+ making sure that the SUPPORTED_Pause and SUPPORTED_AsymPause bits are set in
+ MII_ADVERTISE to indicate towards the link partner that the Ethernet MAC
+ controller supports such a thing. Since flow control/pause frames generation
+ involves the Ethernet MAC driver, it is recommended that this driver takes care
+ of properly indicating advertisement and support for such features by setting
+ the SUPPORTED_Pause and SUPPORTED_AsymPause bits accordingly. This can be done
+ either before or after phy_connect() and/or as a result of implementing the
+ ethtool::set_pauseparam feature.
+
+
+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);
+
+   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, documented
+ in include/linux/phy.h under the phy_driver structure.
+
+ 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.
+
+ When phy_register_fixup() or *_for_uid()/*_for_id() is called at module,
+ unregister fixup and free allocate memory are required.
+
+ Call one of following function before unloading module.
+
+ int phy_unregister_fixup(const char *phy_id, u32 phy_uid, u32 phy_uid_mask);
+ int phy_unregister_fixup_for_uid(u32 phy_uid, u32 phy_uid_mask);
+ int phy_register_fixup_for_id(const char *phy_id);
+
+Standards
+
+ IEEE Standard 802.3: CSMA/CD Access Method and Physical Layer Specifications, Section Two:
+ http://standards.ieee.org/getieee802/download/802.3-2008_section2.pdf
+
+ RGMII v1.3:
+ http://web.archive.org/web/20160303212629/http://www.hp.com/rnd/pdfs/RGMIIv1_3.pdf
+
+ RGMII v2.0:
+ http://web.archive.org/web/20160303171328/http://www.hp.com/rnd/pdfs/RGMIIv2_0_final_hp.pdf