Message-ID: <326391fb-d6ed-31dc-147e-b4ee3914d82f@gmail.com>
Date:   Sat, 26 Jan 2019 11:25:37 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        David Miller <davem@...emloft.net>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: [PATCH net-next] Documentation: net: phy: switch documentation to rst
 format

Switch phylib documentation to rst format.

Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
---
 Documentation/networking/index.rst |   1 +
 Documentation/networking/phy.rst   | 447 +++++++++++++++++++++++++++++
 Documentation/networking/phy.txt   | 429 ---------------------------
 3 files changed, 448 insertions(+), 429 deletions(-)
 create mode 100644 Documentation/networking/phy.rst
 delete mode 100644 Documentation/networking/phy.txt

diff --git a/Documentation/networking/index.rst b/Documentation/networking/index.rst
index 9c313958b..1266dc6d9 100644
--- a/Documentation/networking/index.rst
+++ b/Documentation/networking/index.rst
@@ -29,6 +29,7 @@ Contents:
    msg_zerocopy
    failover
    net_failover
+   phy
    alias
    bridge
    snmp_counter
diff --git a/Documentation/networking/phy.rst b/Documentation/networking/phy.rst
new file mode 100644
index 000000000..37d10695f
--- /dev/null
+++ b/Documentation/networking/phy.rst
@@ -0,0 +1,447 @@
+=====================
+PHY Abstraction Layer
+=====================
+
+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:
+
+#. Increase code-reuse
+#. Increase overall code-maintainability
+#. 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.
+
+#. 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
+
+#. A reset function is optional. This is used to return the bus to an
+   initialized state.
+
+#. 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).
+ 
+#. Like any driver, the device_driver structure must be configured, and init
+   exit functions are used to register the driver.
+
+#. 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:
+
+#. The PAL handles everything, and only calls the network driver when
+   the link state changes, so it can react.
+
+#. The PAL handles everything except interrupts (usually because the
+   controller has the interrupt registers).
+
+#. 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.
+ 
+#. 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 the MAC interrupt of your network driver
+also handles PHY status changes, just set phydev->irq to PHY_IGNORE_INTERRUPT
+before you call phy_start and use phy_mac_interrupt() from the network
+driver. If you don't want to use interrupts, set phydev->irq to PHY_POLL.
+phy_start() enables the PHY interrupts (if applicable) and starts the
+phylib state machine.
+
+When you want to disconnect from the network (even if just briefly), you call
+phy_stop(phydev). This function also stops the phylib state machine and
+disables PHY interrupts.
+
+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.
+::
+
+ void phy_request_interrupt(struct phy_device *phydev);
+
+Requests the IRQ for the PHY interrupts.
+::
+
+ 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
diff --git a/Documentation/networking/phy.txt b/Documentation/networking/phy.txt
deleted file mode 100644
index 7ecba4fd6..000000000
--- a/Documentation/networking/phy.txt
+++ /dev/null
@@ -1,429 +0,0 @@
-
--------
-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 the MAC interrupt of your network driver
- also handles PHY status changes, just set phydev->irq to PHY_IGNORE_INTERRUPT
- before you call phy_start and use phy_mac_interrupt() from the network
- driver. If you don't want to use interrupts, set phydev->irq to PHY_POLL.
- phy_start() enables the PHY interrupts (if applicable) and starts the
- phylib state machine.
-
- When you want to disconnect from the network (even if just briefly), you call
- phy_stop(phydev). This function also stops the phylib state machine and
- disables PHY interrupts.
-
-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.
-
- void phy_request_interrupt(struct phy_device *phydev);
-
-   Requests the IRQ for the PHY interrupts.
-
- 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
-- 
2.20.1

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