snpnet.c

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/*
 * Copyright (C) 2014 Michael Brown <mbrown@fensystems.co.uk>.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301, USA.
 */

FILE_LICENCE ( GPL2_OR_LATER );
FILE_SECBOOT ( PERMITTED );

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <ipxe/iobuf.h>
#include <ipxe/netdevice.h>
#include <ipxe/ethernet.h>
#include <ipxe/if_ether.h>
#include <ipxe/vsprintf.h>
#include <ipxe/timer.h>
#include <ipxe/efi/efi.h>
#include <ipxe/efi/Protocol/SimpleNetwork.h>
#include <ipxe/efi/efi_driver.h>
#include <ipxe/efi/efi_utils.h>
#include <ipxe/efi/efi_snp.h>
#include "snpnet.h"

/** @file
 *
 * SNP NIC driver
 *
 */

/** An SNP NIC */
struct snp_nic {
        /** EFI device */
        struct efi_device *efidev;
        /** Simple network protocol */
        EFI_SIMPLE_NETWORK_PROTOCOL *snp;
        /** Generic device */
        struct device dev;

        /** Maximum packet size
         *
         * This is calculated as the sum of MediaHeaderSize and
         * MaxPacketSize, and may therefore be an overestimate.
         */
        size_t mtu;

        /** Current transmit buffer */
        struct io_buffer *txbuf;
        /** Current receive buffer */
        struct io_buffer *rxbuf;
};

/** Maximum number of received packets per poll */
#define SNP_RX_QUOTA 4

/** Maximum initialisation retry count */
#define SNP_INITIALIZE_RETRY_MAX 10

/** Delay between each initialisation retry */
#define SNP_INITIALIZE_RETRY_DELAY_MS 10

/** Additional padding for receive buffers
 *
 * Some SNP implementations seem to require additional space in the
 * allocated receive buffers, otherwise full-length packets will be
 * silently dropped.
 *
 * The EDK2 MnpDxe driver happens to allocate an additional 8 bytes of
 * padding (4 for a VLAN tag, 4 for the Ethernet frame checksum).
 * Match this behaviour since drivers are very likely to have been
 * tested against MnpDxe.
 */
#define SNP_RX_PAD 8

/** An SNP interface patch to inhibit shutdown for insomniac devices */
struct snp_insomniac_patch {
        /** Original Shutdown() method */
        EFI_SIMPLE_NETWORK_SHUTDOWN shutdown;
        /** Original Stop() method */
        EFI_SIMPLE_NETWORK_STOP stop;
};

/**
 * Format SNP MAC address (for debugging)
 *
 * @v mac               MAC address
 * @v len               Length of MAC address
 * @ret text            MAC address as text
 */
static const char * snpnet_mac_text ( EFI_MAC_ADDRESS *mac, size_t len ) {
        static char buf[ sizeof ( *mac ) * 3 /* "xx:" or "xx\0" */ ];
        size_t used = 0;
        unsigned int i;

        for ( i = 0 ; i < len ; i++ ) {
                used += ssnprintf ( &buf[used], ( sizeof ( buf ) - used ),
                                    "%s%02x", ( used ? ":" : "" ),
                                    mac->Addr[i] );
        }
        return buf;
}

/**
 * Dump SNP mode information (for debugging)
 *
 * @v netdev            Network device
 */
static void snpnet_dump_mode ( struct net_device *netdev ) {
        struct snp_nic *snp = netdev->priv;
        EFI_SIMPLE_NETWORK_MODE *mode = snp->snp->Mode;
        size_t mac_len = mode->HwAddressSize;
        unsigned int i;

        /* Do nothing unless debugging is enabled */
        if ( ! DBG_EXTRA )
                return;

        DBGC2 ( snp, "SNP %s st %d type %d hdr %d pkt %d rxflt %#x/%#x%s "
                "nvram %d acc %d mcast %d/%d\n", netdev->name, mode->State,
                mode->IfType, mode->MediaHeaderSize, mode->MaxPacketSize,
                mode->ReceiveFilterSetting, mode->ReceiveFilterMask,
                ( mode->MultipleTxSupported ? " multitx" : "" ),
                mode->NvRamSize, mode->NvRamAccessSize,
                mode->MCastFilterCount, mode->MaxMCastFilterCount );
        DBGC2 ( snp, "SNP %s hw %s", netdev->name,
                snpnet_mac_text ( &mode->PermanentAddress, mac_len ) );
        DBGC2 ( snp, " addr %s%s",
                snpnet_mac_text ( &mode->CurrentAddress, mac_len ),
                ( mode->MacAddressChangeable ? "" : "(f)" ) );
        DBGC2 ( snp, " bcast %s\n",
                snpnet_mac_text ( &mode->BroadcastAddress, mac_len ) );
        for ( i = 0 ; i < mode->MCastFilterCount ; i++ ) {
                DBGC2 ( snp, "SNP %s mcast %s\n", netdev->name,
                        snpnet_mac_text ( &mode->MCastFilter[i], mac_len ) );
        }
        DBGC2 ( snp, "SNP %s media %s\n", netdev->name,
                ( mode->MediaPresentSupported ?
                  ( mode->MediaPresent ? "present" : "not present" ) :
                  "presence not supported" ) );
}

/**
 * Check link state
 *
 * @v netdev            Network device
 */
static void snpnet_check_link ( struct net_device *netdev ) {
        struct snp_nic *snp = netdev->priv;
        EFI_SIMPLE_NETWORK_MODE *mode = snp->snp->Mode;

        /* Do nothing unless media presence detection is supported */
        if ( ! mode->MediaPresentSupported )
                return;

        /* Report any link status change */
        if ( mode->MediaPresent && ( ! netdev_link_ok ( netdev ) ) ) {
                netdev_link_up ( netdev );
        } else if ( ( ! mode->MediaPresent ) && netdev_link_ok ( netdev ) ) {
                netdev_link_down ( netdev );
        }
}

/**
 * Transmit packet
 *
 * @v netdev            Network device
 * @v iobuf             I/O buffer
 * @ret rc              Return status code
 */
static int snpnet_transmit ( struct net_device *netdev,
                             struct io_buffer *iobuf ) {
        struct snp_nic *snp = netdev->priv;
        EFI_STATUS efirc;
        int rc;

        /* Do nothing if shutdown is in progress */
        if ( efi_shutdown_in_progress )
                return -ECANCELED;

        /* Defer the packet if there is already a transmission in progress */
        if ( snp->txbuf ) {
                netdev_tx_defer ( netdev, iobuf );
                return 0;
        }

        /* Pad to minimum Ethernet length, to work around underlying
         * drivers that do not correctly handle frame padding
         * themselves.
         */
        iob_pad ( iobuf, ETH_ZLEN );

        /* Transmit packet */
        if ( ( efirc = snp->snp->Transmit ( snp->snp, 0, iob_len ( iobuf ),
                                            iobuf->data, NULL, NULL,
                                            NULL ) ) != 0 ) {
                rc = -EEFI ( efirc );
                DBGC ( snp, "SNP %s could not transmit: %s\n",
                       netdev->name, strerror ( rc ) );
                return rc;
        }
        snp->txbuf = iobuf;

        return 0;
}

/**
 * Poll for completed packets
 *
 * @v netdev            Network device
 */
static void snpnet_poll_tx ( struct net_device *netdev ) {
        struct snp_nic *snp = netdev->priv;
        struct io_buffer *iobuf;
        UINT32 irq;
        VOID *txbuf;
        EFI_STATUS efirc;
        int rc;

        /* Get status */
        txbuf = NULL;
        if ( ( efirc = snp->snp->GetStatus ( snp->snp, &irq, &txbuf ) ) != 0 ) {
                rc = -EEFI ( efirc );
                DBGC ( snp, "SNP %s could not get status: %s\n",
                       netdev->name, strerror ( rc ) );
                netdev_rx_err ( netdev, NULL, rc );
                return;
        }

        /* Do nothing unless we have a completion */
        if ( ! txbuf )
                return;

        /* Sanity check */
        if ( ! snp->txbuf ) {
                DBGC ( snp, "SNP %s reported spurious TX completion\n",
                       netdev->name );
                netdev_tx_err ( netdev, NULL, -EPIPE );
                return;
        }

        /* Complete transmission */
        iobuf = snp->txbuf;
        snp->txbuf = NULL;
        netdev_tx_complete ( netdev, iobuf );
}

/**
 * Poll for received packets
 *
 * @v netdev            Network device
 */
static void snpnet_poll_rx ( struct net_device *netdev ) {
        struct snp_nic *snp = netdev->priv;
        UINTN len;
        unsigned int quota;
        EFI_STATUS efirc;
        int rc;

        /* Retrieve up to SNP_RX_QUOTA packets */
        for ( quota = SNP_RX_QUOTA ; quota ; quota-- ) {

                /* Allocate buffer, if required */
                if ( ! snp->rxbuf ) {
                        snp->rxbuf = alloc_iob ( snp->mtu + SNP_RX_PAD );
                        if ( ! snp->rxbuf ) {
                                /* Leave for next poll */
                                break;
                        }
                }

                /* Receive packet */
                len = iob_tailroom ( snp->rxbuf );
                if ( ( efirc = snp->snp->Receive ( snp->snp, NULL, &len,
                                                   snp->rxbuf->data, NULL,
                                                   NULL, NULL ) ) != 0 ) {

                        /* EFI_NOT_READY is just the usual "no packet"
                         * status indication; ignore it.
                         */
                        if ( efirc == EFI_NOT_READY )
                                break;

                        /* Anything else is an error */
                        rc = -EEFI ( efirc );
                        DBGC ( snp, "SNP %s could not receive: %s\n",
                               netdev->name, strerror ( rc ) );
                        netdev_rx_err ( netdev, NULL, rc );
                        break;
                }

                /* Hand off to network stack */
                iob_put ( snp->rxbuf, len );
                netdev_rx ( netdev, snp->rxbuf );
                snp->rxbuf = NULL;
        }
}

/**
 * Poll for completed packets
 *
 * @v netdev            Network device
 */
static void snpnet_poll ( struct net_device *netdev ) {

        /* Do nothing if shutdown is in progress */
        if ( efi_shutdown_in_progress )
                return;

        /* Process any TX completions */
        snpnet_poll_tx ( netdev );

        /* Process any RX completions */
        snpnet_poll_rx ( netdev );

        /* Check for link state changes */
        snpnet_check_link ( netdev );
}

/**
 * Set receive filters
 *
 * @v netdev            Network device
 * @ret rc              Return status code
 */
static int snpnet_rx_filters ( struct net_device *netdev ) {
        struct snp_nic *snp = netdev->priv;
        UINT32 filters[] = {
                snp->snp->Mode->ReceiveFilterMask,
                ( EFI_SIMPLE_NETWORK_RECEIVE_UNICAST |
                  EFI_SIMPLE_NETWORK_RECEIVE_MULTICAST |
                  EFI_SIMPLE_NETWORK_RECEIVE_BROADCAST ),
                ( EFI_SIMPLE_NETWORK_RECEIVE_UNICAST |
                  EFI_SIMPLE_NETWORK_RECEIVE_PROMISCUOUS_MULTICAST |
                  EFI_SIMPLE_NETWORK_RECEIVE_BROADCAST ),
                ( EFI_SIMPLE_NETWORK_RECEIVE_UNICAST |
                  EFI_SIMPLE_NETWORK_RECEIVE_BROADCAST ),
                ( EFI_SIMPLE_NETWORK_RECEIVE_UNICAST ),
        };
        unsigned int i;
        EFI_STATUS efirc;
        int rc;

        /* Try possible receive filters in turn */
        for ( i = 0; i < ( sizeof ( filters ) / sizeof ( filters[0] ) ); i++ ) {
                efirc = snp->snp->ReceiveFilters ( snp->snp, filters[i],
                                EFI_SIMPLE_NETWORK_RECEIVE_MULTICAST, TRUE,
                                0, NULL );
                if ( efirc == 0 )
                        return 0;
                rc = -EEFI ( efirc );
                DBGC ( snp, "SNP %s could not set receive filters %#02x (have "
                       "%#02x): %s\n", netdev->name, filters[i],
                       snp->snp->Mode->ReceiveFilterSetting, strerror ( rc ) );
        }

        return rc;
}

/**
 * Open network device
 *
 * @v netdev            Network device
 * @ret rc              Return status code
 */
static int snpnet_open ( struct net_device *netdev ) {
        struct snp_nic *snp = netdev->priv;
        EFI_MAC_ADDRESS *mac = ( ( void * ) netdev->ll_addr );
        EFI_SIMPLE_NETWORK_MODE *mode = snp->snp->Mode;
        EFI_STATUS efirc;
        unsigned int retry;
        int rc;

        /* Try setting MAC address (before initialising) */
        if ( ( efirc = snp->snp->StationAddress ( snp->snp, FALSE, mac ) ) !=0){
                rc = -EEFI ( efirc );
                DBGC ( snp, "SNP %s could not set station address before "
                       "initialising: %s\n", netdev->name, strerror ( rc ) );
                /* Ignore error */
        }

        /* Initialise NIC, retrying multiple times if link stays down */
        for ( retry = 0 ; ; ) {

                /* Initialise NIC, if not already initialised */
                if ( ( mode->State != EfiSimpleNetworkInitialized ) &&
                     ( ( efirc = snp->snp->Initialize ( snp->snp,
                                                        0, 0 ) ) != 0 ) ) {
                        rc = -EEFI ( efirc );
                        snpnet_dump_mode ( netdev );
                        DBGC ( snp, "SNP %s could not initialise: %s\n",
                               netdev->name, strerror ( rc ) );
                        return rc;
                }

                /* Stop if we have link up (or no link detection capability) */
                if ( ( ! mode->MediaPresentSupported ) || mode->MediaPresent )
                        break;

                /* Stop if we have exceeded our retry count.  This is
                 * not a failure; it is plausible that we genuinely do
                 * not have link up.
                 */
                if ( ++retry >= SNP_INITIALIZE_RETRY_MAX )
                        break;
                DBGC ( snp, "SNP %s retrying initialisation (retry %d)\n",
                       netdev->name, retry );

                /* Delay to allow time for link to establish */
                mdelay ( SNP_INITIALIZE_RETRY_DELAY_MS );

                /* Shut down and retry (unless device is insomniac);
                 * this is sometimes necessary in order to persuade
                 * the underlying SNP driver to actually update the
                 * link state.
                 */
                if ( ( ! netdev_insomniac ( netdev ) ) &&
                     ( ( efirc = snp->snp->Shutdown ( snp->snp ) ) != 0 ) ) {
                        rc = -EEFI ( efirc );
                        snpnet_dump_mode ( netdev );
                        DBGC ( snp, "SNP %s could not shut down: %s\n",
                               netdev->name, strerror ( rc ) );
                        return rc;
                }
        }

        /* Try setting MAC address (after initialising) */
        if ( ( efirc = snp->snp->StationAddress ( snp->snp, FALSE, mac ) ) !=0){
                rc = -EEFI ( efirc );
                DBGC ( snp, "SNP %s could not set station address after "
                       "initialising: %s\n", netdev->name, strerror ( rc ) );
                /* Ignore error */
        }

        /* Set receive filters */
        if ( ( rc = snpnet_rx_filters ( netdev ) ) != 0 ) {
                /* Ignore error */
        }

        /* Dump mode information (for debugging) */
        snpnet_dump_mode ( netdev );

        return 0;
}

/**
 * Close network device
 *
 * @v netdev            Network device
 */
static void snpnet_close ( struct net_device *netdev ) {
        struct snp_nic *snp = netdev->priv;
        EFI_STATUS efirc;
        int rc;

        /* Shut down NIC (unless whole system shutdown is in progress,
         * or device is insomniac).
         */
        if ( ( ! efi_shutdown_in_progress ) &&
             ( ! netdev_insomniac ( netdev ) ) &&
             ( ( efirc = snp->snp->Shutdown ( snp->snp ) ) != 0 ) ) {
                rc = -EEFI ( efirc );
                DBGC ( snp, "SNP %s could not shut down: %s\n",
                       netdev->name, strerror ( rc ) );
                /* Nothing we can do about this */
        }

        /* Discard transmit buffer, if applicable */
        if ( snp->txbuf ) {
                netdev_tx_complete_err ( netdev, snp->txbuf, -ECANCELED );
                snp->txbuf = NULL;
        }

        /* Discard receive buffer, if applicable */
        if ( snp->rxbuf ) {
                free_iob ( snp->rxbuf );
                snp->rxbuf = NULL;
        }
}

/** SNP network device operations */
static struct net_device_operations snpnet_operations = {
        .open = snpnet_open,
        .close = snpnet_close,
        .transmit = snpnet_transmit,
        .poll = snpnet_poll,
};

/**
 * Check to see if driver supports a device
 *
 * @v device            EFI device handle
 * @v protocol          Protocol GUID
 * @v inhibit_wifi      Inhibit wireless devices
 * @ret rc              Return status code
 */
int snpnet_supported ( EFI_HANDLE device, EFI_GUID *protocol,
                       int inhibit_wifi ) {
        EFI_HANDLE parent;
        int rc;

        /* Check that this is not a device we are providing ourselves */
        if ( find_snpdev ( device ) != NULL ) {
                DBGCP ( device, "HANDLE %s is provided by this binary\n",
                        efi_handle_name ( device ) );
                return -ENOTTY;
        }

        /* Test for presence of protocol */
        if ( ( rc = efi_test ( device, protocol ) ) != 0 ) {
                DBGCP ( device, "HANDLE %s is not a %s device\n",
                        efi_handle_name ( device ),
                        efi_guid_ntoa ( protocol ) );
                return rc;
        }

        /* Check that there are no instances of this protocol further
         * up this device path.
         */
        if ( ( rc = efi_locate_device ( device, protocol,
                                        &parent, 1 ) ) == 0 ) {
                DBGC2 ( device, "HANDLE %s has %s-supporting parent ",
                        efi_handle_name ( device ),
                        efi_guid_ntoa ( protocol ) );
                DBGC2 ( device, "%s\n", efi_handle_name ( parent ) );
                return -ENOTTY;
        }
        DBGC ( device, "HANDLE %s is a %s device\n",
               efi_handle_name ( device ), efi_guid_ntoa ( protocol ) );

        /* Check for wireless devices, if applicable */
        if ( inhibit_wifi &&
             ( ( efi_test ( device, &efi_wifi2_protocol_guid ) ) == 0 ) ) {
                DBGC ( device, "HANDLE %s is wireless: assuming vendor %s "
                       "driver is too unreliable to use\n",
                       efi_handle_name ( device ),
                       efi_guid_ntoa ( protocol ) );
                return -ENOTTY;
        }

        return 0;
}

/**
 * Check if device must be insomniac
 *
 * @v device            EFI device handle
 * @v is_insomniac      Device must be insomniac
 */
static int snpnet_is_insomniac ( EFI_HANDLE device ) {
        int rc;

        /* Check for wireless devices
         *
         * The UEFI model for wireless network configuration is
         * somewhat underdefined.  At the time of writing, the EDK2
         * "UEFI WiFi Connection Manager" driver provides only one way
         * to configure wireless network credentials, which is to
         * enter them interactively via an HII form.  Credentials are
         * not stored (or exposed via any protocol interface), and so
         * any temporary disconnection from the wireless network will
         * inevitably leave the interface in an unusable state that
         * cannot be recovered without user intervention.
         *
         * Experimentation shows that at least some wireless network
         * drivers will disconnect from the wireless network when the
         * SNP Shutdown() method is called, or if the device is not
         * polled sufficiently frequently to maintain its association
         * to the network.  We therefore inhibit calls to Shutdown()
         * and Stop() for any such SNP protocol interfaces, and mark
         * our network device as insomniac so that it will be polled
         * even when closed.
         */
        if ( ( rc = efi_test ( device, &efi_wifi2_protocol_guid ) ) == 0 ) {
                DBGC ( device, "SNP %s is wireless: assuming insomniac\n",
                       efi_handle_name ( device ) );
                return 1;
        }

        return 0;
}

/**
 * Ignore shutdown attempt
 *
 * @v snp               SNP interface
 * @ret efirc           EFI status code
 */
static EFI_STATUS EFIAPI
snpnet_do_nothing ( EFI_SIMPLE_NETWORK_PROTOCOL *snp __unused ) {

        return 0;
}

/**
 * Patch SNP protocol interface to prevent shutdown
 *
 * @v device            EFI device handle
 * @v patch             Interface patch
 * @ret rc              Return status code
 */
static int snpnet_insomniac_patch ( EFI_HANDLE device,
                                    struct snp_insomniac_patch *patch ) {
        EFI_SIMPLE_NETWORK_PROTOCOL *interface;
        int rc;

        /* Open interface for ephemeral use */
        if ( ( rc = efi_open ( device, &efi_simple_network_protocol_guid,
                               &interface ) ) != 0 ) {
                DBGC ( device, "SNP %s cannot open SNP protocol for patching: "
                       "%s\n", efi_handle_name ( device ), strerror ( rc ) );
                return rc;
        }

        /* Record original Shutdown() and Stop() methods */
        patch->shutdown = interface->Shutdown;
        patch->stop = interface->Stop;

        /* Inhibit other UEFI drivers' calls to Shutdown() and Stop()
         *
         * This is necessary since disconnecting the MnpDxe driver
         * will attempt to shut down the SNP device, which would leave
         * us with an unusable device.
         */
        interface->Shutdown = snpnet_do_nothing;
        interface->Stop = snpnet_do_nothing;
        DBGC ( device, "SNP %s patched to inhibit shutdown\n",
               efi_handle_name ( device ) );

        return 0;
}

/**
 * Restore patched SNP protocol interface
 *
 * @v device            EFI device handle
 * @v patch             Interface patch to fill in
 * @ret rc              Return status code
 */
static int snpnet_insomniac_restore ( EFI_HANDLE device,
                                      struct snp_insomniac_patch *patch ) {
        EFI_SIMPLE_NETWORK_PROTOCOL *interface;
        int rc;

        /* Avoid returning uninitialised data on error */
        memset ( patch, 0, sizeof ( *patch ) );

        /* Open interface for ephemeral use */
        if ( ( rc = efi_open ( device, &efi_simple_network_protocol_guid,
                               &interface ) ) != 0 ) {
                DBGC ( device, "SNP %s cannot open patched SNP protocol: %s\n",
                       efi_handle_name ( device ), strerror ( rc ) );
                return rc;
        }

        /* Restore original Shutdown() and Stop() methods, if possible */
        if ( interface->Shutdown == snpnet_do_nothing )
                interface->Shutdown = patch->shutdown;
        if ( interface->Stop == snpnet_do_nothing )
                interface->Stop = patch->stop;

        /* Check that original methods were restored (by us or others) */
        if ( ( interface->Shutdown != patch->shutdown ) ||
             ( interface->Stop != patch->stop ) ) {
                DBGC ( device, "SNP %s could not restore patched SNP "
                       "protocol\n", efi_handle_name ( device ) );
                return -EBUSY;
        }

        return 0;
}

/**
 * Exclude existing drivers
 *
 * @v device            EFI device handle
 * @ret rc              Return status code
 */
int snpnet_exclude ( EFI_HANDLE device ) {
        EFI_GUID *protocol = &efi_simple_network_protocol_guid;
        struct snp_insomniac_patch patch;
        int insomniac;
        int rc;

        /* Check if this is a device that must not ever be shut down */
        insomniac = snpnet_is_insomniac ( device );

        /* Inhibit calls to Shutdown() and Stop(), if applicable */
        if ( insomniac &&
             ( ( rc = snpnet_insomniac_patch ( device, &patch ) ) != 0 ) ) {
                goto err_patch;
        }

        /* Exclude existing SNP drivers */
        if ( ( rc = efi_driver_exclude ( device, protocol ) ) != 0 ) {
                DBGC ( device, "SNP %s could not exclude drivers: %s\n",
                       efi_handle_name ( device ), strerror ( rc ) );
                goto err_exclude;
        }

 err_exclude:
        if ( insomniac )
                snpnet_insomniac_restore ( device, &patch );
 err_patch:
        return rc;
}

/**
 * Attach driver to device
 *
 * @v efidev            EFI device
 * @ret rc              Return status code
 */
int snpnet_start ( struct efi_device *efidev ) {
        EFI_HANDLE device = efidev->device;
        EFI_SIMPLE_NETWORK_PROTOCOL *interface;
        EFI_SIMPLE_NETWORK_MODE *mode;
        struct net_device *netdev;
        struct snp_nic *snp;
        EFI_STATUS efirc;
        int rc;

        /* Open SNP protocol */
        if ( ( rc = efi_open_by_driver ( device,
                                         &efi_simple_network_protocol_guid,
                                         &interface ) ) != 0 ) {
                DBGC ( device, "SNP %s cannot open SNP protocol: %s\n",
                       efi_handle_name ( device ), strerror ( rc ) );
                DBGC_EFI_OPENERS ( device, device,
                                   &efi_simple_network_protocol_guid );
                goto err_open_protocol;
        }

        /* Allocate and initialise structure */
        netdev = alloc_etherdev ( sizeof ( *snp ) );
        if ( ! netdev ) {
                rc = -ENOMEM;
                goto err_alloc;
        }
        netdev_init ( netdev, &snpnet_operations );
        snp = netdev->priv;
        snp->efidev = efidev;
        snp->snp = interface;
        mode = snp->snp->Mode;
        efidev_set_drvdata ( efidev, netdev );

        /* Populate underlying device information */
        efi_device_info ( device, "SNP", &snp->dev );
        snp->dev.driver_name = "SNP";
        snp->dev.parent = &efidev->dev;
        list_add ( &snp->dev.siblings, &efidev->dev.children );
        INIT_LIST_HEAD ( &snp->dev.children );
        netdev->dev = &snp->dev;

        /* Check if device is insomniac */
        if ( snpnet_is_insomniac ( device ) )
                netdev->state |= NETDEV_INSOMNIAC;

        /* Bring to the correct state for a closed interface */
        if ( ( mode->State == EfiSimpleNetworkStopped ) &&
             ( ( efirc = snp->snp->Start ( snp->snp ) ) != 0 ) ) {
                rc = -EEFI ( efirc );
                DBGC ( device, "SNP %s could not start: %s\n",
                       efi_handle_name ( device ), strerror ( rc ) );
                goto err_start;
        }
        if ( ( mode->State == EfiSimpleNetworkInitialized ) &&
             ( ! netdev_insomniac ( netdev ) ) &&
             ( ( efirc = snp->snp->Shutdown ( snp->snp ) ) != 0 ) ) {
                rc = -EEFI ( efirc );
                DBGC ( device, "SNP %s could not shut down: %s\n",
                       efi_handle_name ( device ), strerror ( rc ) );
                goto err_shutdown;
        }

        /* Populate network device parameters */
        if ( mode->HwAddressSize != netdev->ll_protocol->hw_addr_len ) {
                DBGC ( device, "SNP %s has invalid hardware address length "
                       "%d\n", efi_handle_name ( device ), mode->HwAddressSize);
                rc = -ENOTSUP;
                goto err_hw_addr_len;
        }
        memcpy ( netdev->hw_addr, &mode->PermanentAddress,
                 netdev->ll_protocol->hw_addr_len );
        if ( mode->HwAddressSize != netdev->ll_protocol->ll_addr_len ) {
                DBGC ( device, "SNP %s has invalid link-layer address length "
                       "%d\n", efi_handle_name ( device ), mode->HwAddressSize);
                rc = -ENOTSUP;
                goto err_ll_addr_len;
        }
        memcpy ( netdev->ll_addr, &mode->CurrentAddress,
                 netdev->ll_protocol->ll_addr_len );
        snp->mtu = ( snp->snp->Mode->MaxPacketSize +
                     snp->snp->Mode->MediaHeaderSize );

        /* Register network device */
        if ( ( rc = register_netdev ( netdev ) ) != 0 )
                goto err_register_netdev;
        DBGC ( device, "SNP %s registered as %s\n",
               efi_handle_name ( device ), netdev->name );

        /* Set initial link state */
        if ( snp->snp->Mode->MediaPresentSupported ) {
                snpnet_check_link ( netdev );
        } else {
                netdev_link_up ( netdev );
        }

        return 0;

        unregister_netdev ( netdev );
 err_register_netdev:
 err_ll_addr_len:
 err_hw_addr_len:
 err_shutdown:
 err_start:
        list_del ( &snp->dev.siblings );
        netdev_nullify ( netdev );
        netdev_put ( netdev );
 err_alloc:
        efi_close_by_driver ( device, &efi_simple_network_protocol_guid );
 err_open_protocol:
        return rc;
}

/**
 * Detach driver from device
 *
 * @v efidev            EFI device
  */
void snpnet_stop ( struct efi_device *efidev ) {
        struct net_device *netdev = efidev_get_drvdata ( efidev );
        struct snp_nic *snp = netdev->priv;
        EFI_HANDLE device = efidev->device;
        EFI_STATUS efirc;
        int rc;

        /* Unregister network device */
        unregister_netdev ( netdev );

        /* Stop SNP protocol (unless whole system shutdown is in progress) */
        if ( ( ! efi_shutdown_in_progress ) &&
             ( ( efirc = snp->snp->Stop ( snp->snp ) ) != 0 ) ) {
                rc = -EEFI ( efirc );
                DBGC ( device, "SNP %s could not stop: %s\n",
                       efi_handle_name ( device ), strerror ( rc ) );
                /* Nothing we can do about this */
        }

        /* Free network device */
        list_del ( &snp->dev.siblings );
        netdev_nullify ( netdev );
        netdev_put ( netdev );

        /* Close SNP protocol */
        efi_close_by_driver ( device, &efi_simple_network_protocol_guid );
}