DPAA2 MAC / PHY support¶
- Copyright:
- © 2019 NXP 
Overview¶
The DPAA2 MAC / PHY support consists of a set of APIs that help DPAA2 network drivers (dpaa2-eth, dpaa2-ethsw) interact with the PHY library.
DPAA2 Software Architecture¶
Among other DPAA2 objects, the fsl-mc bus exports DPNI objects (abstracting a network interface) and DPMAC objects (abstracting a MAC). The dpaa2-eth driver probes on the DPNI object and connects to and configures a DPMAC object with the help of phylink.
Data connections may be established between a DPNI and a DPMAC, or between two DPNIs. Depending on the connection type, the netif_carrier_[on/off] is handled directly by the dpaa2-eth driver or by phylink.
Sources of abstracted link state information presented by the MC firmware
                                             +--------------------------------------+
+------------+                  +---------+  |                           xgmac_mdio |
| net_device |                  | phylink |--|  +-----+  +-----+  +-----+  +-----+  |
+------------+                  +---------+  |  | PHY |  | PHY |  | PHY |  | PHY |  |
      |                             |        |  +-----+  +-----+  +-----+  +-----+  |
    +------------------------------------+   |                    External MDIO bus |
    |            dpaa2-eth               |   +--------------------------------------+
    +------------------------------------+
      |                             |                                           Linux
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      |                             |                                     MC firmware
      |              /|             V
+----------+        / |       +----------+
|          |       /  |       |          |
|          |       |  |       |          |
|   DPNI   |<------|  |<------|   DPMAC  |
|          |       |  |       |          |
|          |       \  |<---+  |          |
+----------+        \ |    |  +----------+
                     \|    |
                           |
         +--------------------------------------+
         | MC firmware polling MAC PCS for link |
         |  +-----+  +-----+  +-----+  +-----+  |
         |  | PCS |  | PCS |  | PCS |  | PCS |  |
         |  +-----+  +-----+  +-----+  +-----+  |
         |                    Internal MDIO bus |
         +--------------------------------------+
Depending on an MC firmware configuration setting, each MAC may be in one of two modes:
- DPMAC_LINK_TYPE_FIXED: the link state management is handled exclusively by the MC firmware by polling the MAC PCS. Without the need to register a phylink instance, the dpaa2-eth driver will not bind to the connected dpmac object at all. 
- DPMAC_LINK_TYPE_PHY: The MC firmware is left waiting for link state update events, but those are in fact passed strictly between the dpaa2-mac (based on phylink) and its attached net_device driver (dpaa2-eth, dpaa2-ethsw), effectively bypassing the firmware. 
Implementation¶
At probe time or when a DPNI’s endpoint is dynamically changed, the dpaa2-eth is responsible to find out if the peer object is a DPMAC and if this is the case, to integrate it with PHYLINK using the dpaa2_mac_connect() API, which will do the following:
look up the device tree for PHYLINK-compatible of binding (phy-handle)
will create a PHYLINK instance associated with the received net_device
connect to the PHY using
phylink_of_phy_connect()
The following phylink_mac_ops callback are implemented:
.validate() will populate the supported linkmodes with the MAC capabilities only when the phy_interface_t is RGMII_* (at the moment, this is the only link type supported by the driver).
.
mac_config()will configure the MAC in the new configuration using the dpmac_set_link_state() MC firmware API.
.
mac_link_up()/ .mac_link_down()will update the MAC link using the same API described above.
At driver unbind() or when the DPNI object is disconnected from the DPMAC, the dpaa2-eth driver calls dpaa2_mac_disconnect() which will, in turn, disconnect from the PHY and destroy the PHYLINK instance.
In case of a DPNI-DPMAC connection, an ‘ip link set dev eth0 up’ would start the following sequence of operations:
- phylink_start()called from .- dev_open().
- The . - mac_config()and .- mac_link_up()callbacks are called by PHYLINK.
- In order to configure the HW MAC, the MC Firmware API dpmac_set_link_state() is called. 
- The firmware will eventually setup the HW MAC in the new configuration. 
- A - netif_carrier_on()call is made directly from PHYLINK on the associated net_device.
- The dpaa2-eth driver handles the LINK_STATE_CHANGE irq in order to enable/disable Rx taildrop based on the pause frame settings. 
+---------+               +---------+
| PHYLINK |-------------->|  eth0   |
+---------+           (5) +---------+
(1) ^  |
    |  |
    |  v (2)
+-----------------------------------+
|             dpaa2-eth             |
+-----------------------------------+
       |                    ^ (6)
       |                    |
       v (3)                |
+---------+---------------+---------+
|  DPMAC  |               |  DPNI   |
+---------+               +---------+
|            MC Firmware            |
+-----------------------------------+
       |
       |
       v (4)
+-----------------------------------+
|             HW MAC                |
+-----------------------------------+
In case of a DPNI-DPNI connection, a usual sequence of operations looks like the following:
- ip link set dev eth0 up 
- The dpni_enable() MC API called on the associated fsl_mc_device. 
- ip link set dev eth1 up 
- The dpni_enable() MC API called on the associated fsl_mc_device. 
- The LINK_STATE_CHANGED irq is received by both instances of the dpaa2-eth driver because now the operational link state is up. 
- The - netif_carrier_on()is called on the exported net_device from link_state_update().
+---------+               +---------+
|  eth0   |               |  eth1   |
+---------+               +---------+
    |  ^                     ^  |
    |  |                     |  |
(1) v  | (6)             (6) |  v (3)
+---------+               +---------+
|dpaa2-eth|               |dpaa2-eth|
+---------+               +---------+
    |  ^                     ^  |
    |  |                     |  |
(2) v  | (5)             (5) |  v (4)
+---------+---------------+---------+
|  DPNI   |               |  DPNI   |
+---------+               +---------+
|            MC Firmware            |
+-----------------------------------+
Exported API¶
Any DPAA2 driver that drivers endpoints of DPMAC objects should service its _EVENT_ENDPOINT_CHANGED irq and connect/disconnect from the associated DPMAC when necessary using the below listed API:
- int dpaa2_mac_connect(struct dpaa2_mac *mac);
- void dpaa2_mac_disconnect(struct dpaa2_mac *mac);
A phylink integration is necessary only when the partner DPMAC is not of
TYPE_FIXED. This means it is either of TYPE_PHY, or of
TYPE_BACKPLANE (the difference being the two that in the TYPE_BACKPLANE
mode, the MC firmware does not access the PCS registers). One can check for
this condition using the following helper:
- static inline bool dpaa2_mac_is_type_phy(struct dpaa2_mac *mac);
Before connection to a MAC, the caller must allocate and populate the dpaa2_mac structure with the associated net_device, a pointer to the MC portal to be used and the actual fsl_mc_device structure of the DPMAC.