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diff --git a/doc/driver-model/ethernet.rst b/doc/driver-model/ethernet.rst new file mode 100644 index 0000000000..359a0523cf --- /dev/null +++ b/doc/driver-model/ethernet.rst @@ -0,0 +1,321 @@ +Ethernet Driver Guide +======================= + +The networking stack in Das U-Boot is designed for multiple network devices +to be easily added and controlled at runtime. This guide is meant for people +who wish to review the net driver stack with an eye towards implementing your +own ethernet device driver. Here we will describe a new pseudo 'APE' driver. + +Most existing drivers do already - and new network driver MUST - use the +U-Boot core driver model. Generic information about this can be found in +doc/driver-model/design.rst, this document will thus focus on the network +specific code parts. +Some drivers are still using the old Ethernet interface, differences between +the two and hints about porting will be handled at the end. + +Driver framework +------------------ + +A network driver following the driver model must declare itself using +the UCLASS_ETH .id field in the U-Boot driver struct: + +.. code-block:: c + + U_BOOT_DRIVER(eth_ape) = { + .name = "eth_ape", + .id = UCLASS_ETH, + .of_match = eth_ape_ids, + .ofdata_to_platdata = eth_ape_ofdata_to_platdata, + .probe = eth_ape_probe, + .ops = ð_ape_ops, + .priv_auto_alloc_size = sizeof(struct eth_ape_priv), + .platdata_auto_alloc_size = sizeof(struct eth_ape_pdata), + .flags = DM_FLAG_ALLOC_PRIV_DMA, + }; + +struct eth_ape_priv contains runtime per-instance data, like buffers, pointers +to current descriptors, current speed settings, pointers to PHY related data +(like struct mii_dev) and so on. Declaring its size in .priv_auto_alloc_size +will let the driver framework allocate it at the right time. +It can be retrieved using a dev_get_priv(dev) call. + +struct eth_ape_pdata contains static platform data, like the MMIO base address, +a hardware variant, the MAC address. ``struct eth_pdata eth_pdata`` +as the first member of this struct helps to avoid duplicated code. +If you don't need any more platform data beside the standard member, +just use sizeof(struct eth_pdata) for the platdata_auto_alloc_size. + +PCI devices add a line pointing to supported vendor/device ID pairs: + +.. code-block:: c + + static struct pci_device_id supported[] = { + { PCI_DEVICE(PCI_VENDOR_ID_APE, 0x4223) }, + {} + }; + + U_BOOT_PCI_DEVICE(eth_ape, supported); + +It is also possible to declare support for a whole class of PCI devices:: + + { PCI_DEVICE_CLASS(PCI_CLASS_SYSTEM_SDHCI << 8, 0xffff00) }, + +Device probing and instantiation will be handled by the driver model framework, +so follow the guidelines there. The probe() function would initialise the +platform specific parts of the hardware, like clocks, resets, GPIOs, the MDIO +bus. Also it would take care of any special PHY setup (power rails, enable +bits for internal PHYs, etc.). + +Driver methods +---------------- + +The real work will be done in the driver method functions the driver provides +by defining the members of struct eth_ops: + +.. code-block:: c + + struct eth_ops { + int (*start)(struct udevice *dev); + int (*send)(struct udevice *dev, void *packet, int length); + int (*recv)(struct udevice *dev, int flags, uchar **packetp); + int (*free_pkt)(struct udevice *dev, uchar *packet, int length); + void (*stop)(struct udevice *dev); + int (*mcast)(struct udevice *dev, const u8 *enetaddr, int join); + int (*write_hwaddr)(struct udevice *dev); + int (*read_rom_hwaddr)(struct udevice *dev); + }; + +An up-to-date version of this struct together with more information can be +found in include/net.h. + +Only start, stop, send and recv are required, the rest are optional and are +handled by generic code or ignored if not provided. + +The **start** function initialises the hardware and gets it ready for send/recv +operations. You often do things here such as resetting the MAC +and/or PHY, and waiting for the link to autonegotiate. You should also take +the opportunity to program the device's MAC address with the enetaddr member +of the generic struct eth_pdata (which would be the first member of your +own platdata struct). This allows the rest of U-Boot to dynamically change +the MAC address and have the new settings be respected. + +The **send** function does what you think -- transmit the specified packet +whose size is specified by length (in bytes). The packet buffer can (and +will!) be reused for subsequent calls to send(), so it must be no longer +used when the send() function returns. The easiest way to achieve this is +to wait until the transmission is complete. Alternatively, if supported by +the hardware, just waiting for the buffer to be consumed (by some DMA engine) +might be an option as well. +Another way of consuming the buffer could be to copy the data to be send, +then just queue the copied packet (for instance handing it over to a DMA +engine), and return immediately afterwards. +In any case you should leave the state such that the send function can be +called multiple times in a row. + +The **recv** function polls for availability of a new packet. If none is +available, it must return with -EAGAIN. +If a packet has been received, make sure it is accessible to the CPU +(invalidate caches if needed), then write its address to the packetp pointer, +and return the length. If there is an error (receive error, too short or too +long packet), return 0 if you require the packet to be cleaned up normally, +or a negative error code otherwise (cleanup not necessary or already done). +The U-Boot network stack will then process the packet. + +If **free_pkt** is defined, U-Boot will call it after a received packet has +been processed, so the packet buffer can be freed or recycled. Typically you +would hand it back to the hardware to acquire another packet. free_pkt() will +be called after recv(), for the same packet, so you don't necessarily need +to infer the buffer to free from the ``packet`` pointer, but can rely on that +being the last packet that recv() handled. +The common code sets up packet buffers for you already in the .bss +(net_rx_packets), so there should be no need to allocate your own. This doesn't +mean you must use the net_rx_packets array however; you're free to use any +buffer you wish. + +The **stop** function should turn off / disable the hardware and place it back +in its reset state. It can be called at any time (before any call to the +related start() function), so make sure it can handle this sort of thing. + +The (optional) **write_hwaddr** function should program the MAC address stored +in pdata->enetaddr into the Ethernet controller. + +So the call graph at this stage would look something like: + +.. code-block:: c + + (some net operation (ping / tftp / whatever...)) + eth_init() + ops->start() + eth_send() + ops->send() + eth_rx() + ops->recv() + (process packet) + if (ops->free_pkt) + ops->free_pkt() + eth_halt() + ops->stop() + + +CONFIG_PHYLIB / CONFIG_CMD_MII +-------------------------------- + +If your device supports banging arbitrary values on the MII bus (pretty much +every device does), you should add support for the mii command. Doing so is +fairly trivial and makes debugging mii issues a lot easier at runtime. + +In your driver's ``probe()`` function, add a call to mdio_alloc() and +mdio_register() like so: + +.. code-block:: c + + bus = mdio_alloc(); + if (!bus) { + ... + return -ENOMEM; + } + + bus->read = ape_mii_read; + bus->write = ape_mii_write; + mdio_register(bus); + +And then define the mii_read and mii_write functions if you haven't already. +Their syntax is straightforward:: + + int mii_read(struct mii_dev *bus, int addr, int devad, int reg); + int mii_write(struct mii_dev *bus, int addr, int devad, int reg, + u16 val); + +The read function should read the register 'reg' from the phy at address 'addr' +and return the result to its caller. The implementation for the write function +should logically follow. + +................................................................ + +Legacy network drivers +------------------------ + +!!! WARNING !!! + +This section below describes the old way of doing things. No new Ethernet +drivers should be implemented this way. All new drivers should be written +against the U-Boot core driver model, as described above. + +The actual callback functions are fairly similar, the differences are: + +- ``start()`` is called ``init()`` +- ``stop()`` is called ``halt()`` +- The ``recv()`` function must loop until all packets have been received, for + each packet it must call the net_process_received_packet() function, + handing it over the pointer and the length. Afterwards it should free + the packet, before checking for new data. + +For porting an old driver to the new driver model, split the existing recv() +function into the actual new recv() function, just fetching **one** packet, +remove the call to net_process_received_packet(), then move the packet +cleanup into the ``free_pkt()`` function. + +Registering the driver and probing a device is handled very differently, +follow the recommendations in the driver model design documentation for +instructions on how to port this over. For the records, the old way of +initialising a network driver is as follows: + +Old network driver registration +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +When U-Boot initializes, it will call the common function eth_initialize(). +This will in turn call the board-specific board_eth_init() (or if that fails, +the cpu-specific cpu_eth_init()). These board-specific functions can do random +system handling, but ultimately they will call the driver-specific register +function which in turn takes care of initializing that particular instance. + +Keep in mind that you should code the driver to avoid storing state in global +data as someone might want to hook up two of the same devices to one board. +Any such information that is specific to an interface should be stored in a +private, driver-defined data structure and pointed to by eth->priv (see below). + +So the call graph at this stage would look something like: + +.. code-block:: c + + board_init() + eth_initialize() + board_eth_init() / cpu_eth_init() + driver_register() + initialize eth_device + eth_register() + +At this point in time, the only thing you need to worry about is the driver's +register function. The pseudo code would look something like: + +.. code-block:: c + + int ape_register(bd_t *bis, int iobase) + { + struct ape_priv *priv; + struct eth_device *dev; + struct mii_dev *bus; + + priv = malloc(sizeof(*priv)); + if (priv == NULL) + return -ENOMEM; + + dev = malloc(sizeof(*dev)); + if (dev == NULL) { + free(priv); + return -ENOMEM; + } + + /* setup whatever private state you need */ + + memset(dev, 0, sizeof(*dev)); + sprintf(dev->name, "APE"); + + /* + * if your device has dedicated hardware storage for the + * MAC, read it and initialize dev->enetaddr with it + */ + ape_mac_read(dev->enetaddr); + + dev->iobase = iobase; + dev->priv = priv; + dev->init = ape_init; + dev->halt = ape_halt; + dev->send = ape_send; + dev->recv = ape_recv; + dev->write_hwaddr = ape_write_hwaddr; + + eth_register(dev); + + #ifdef CONFIG_PHYLIB + bus = mdio_alloc(); + if (!bus) { + free(priv); + free(dev); + return -ENOMEM; + } + + bus->read = ape_mii_read; + bus->write = ape_mii_write; + mdio_register(bus); + #endif + + return 1; + } + +The exact arguments needed to initialize your device are up to you. If you +need to pass more/less arguments, that's fine. You should also add the +prototype for your new register function to include/netdev.h. + +The return value for this function should be as follows: +< 0 - failure (hardware failure, not probe failure) +>=0 - number of interfaces detected + +You might notice that many drivers seem to use xxx_initialize() rather than +xxx_register(). This is the old naming convention and should be avoided as it +causes confusion with the driver-specific init function. + +Other than locating the MAC address in dedicated hardware storage, you should +not touch the hardware in anyway. That step is handled in the driver-specific +init function. Remember that we are only registering the device here, we are +not checking its state or doing random probing. |