The (wired) network stopped working on my cubietruck after upgrading from linux-armv7-4.4.4-1 to linux-armv7-4.5.0-1. Downgrading solves the problem.
These are what seem to me to be the relevant sections from dmesg:
Kernel 4.4.4
$this->bbcode_second_pass_code('', '
[ 9.132863] usbcore: registered new interface driver brcmfmac
[ 9.194437] brcmfmac_sdio mmc1:0001:1: Direct firmware load for brcm/brcmfmac43362-sdio.txt failed with error -2
[ 9.232376] sun7i-dwmac 1c50000.ethernet: no regulator found
[ 9.348095] sun7i-dwmac 1c50000.ethernet: no reset control found
[ 9.355664] Ring mode enabled
[ 9.359442] No HW DMA feature register supported
[ 9.365600] Normal descriptors
[ 9.369014] TX Checksum insertion supported
[ 9.416202] EXT4-fs (sda1): mounted filesystem with ordered data mode. Opts: (null)
[ 9.477857] libphy: stmmac: probed
[ 9.481401] eth0: PHY ID 001cc915 at 0 IRQ POLL (stmmac-0:00) active
[ 9.487930] eth0: PHY ID 001cc915 at 1 IRQ POLL (stmmac-0:01)
[ 9.528289] sun4i-codec 1c22c00.codec: Codec <-> 1c22c00.codec mapping ok
[ 9.811801] systemd-journald[157]: Received request to flush runtime journal from PID 1
[ 10.214014] brcmfmac: brcmf_sdio_htclk: HT Avail timeout (1000000): clkctl 0x50
[ 11.234062] brcmfmac: brcmf_sdio_htclk: HT Avail timeout (1000000): clkctl 0x50
[ 11.807847] nf_conntrack version 0.5.0 (16384 buckets, 65536 max)
[ 11.892802] RX IPC Checksum Offload disabled
[ 11.897400] No MAC Management Counters available
[ 12.091339] Netfilter messages via NETLINK v0.30.
[ 13.884339] sun7i-dwmac 1c50000.ethernet eth0: Link is Up - 1Gbps/Full - flow control rx/tx
')
Kernel 4.5.0
$this->bbcode_second_pass_code('', '
[ 8.171773] usbcore: registered new interface driver brcmfmac
[ 8.222454] brcmfmac_sdio mmc1:0001:1: Direct firmware load for brcm/brcmfmac43362-sdio.txt failed with error -2
[ 8.412232] sun7i-dwmac 1c50000.ethernet: no regulator found
[ 8.425324] sun7i-dwmac 1c50000.ethernet: no reset control found
[ 8.439581] Ring mode enabled
[ 8.442707] No HW DMA feature register supported
[ 8.447313] Normal descriptors
[ 8.450687] TX Checksum insertion supported
[ 8.526840] sun4i-codec 1c22c00.codec: Codec <-> 1c22c00.codec mapping ok
[ 8.754139] EXT4-fs (sda1): mounted filesystem with ordered data mode. Opts: (null)
[ 9.170061] systemd-journald[134]: Received request to flush runtime journal from PID 1
[ 9.248334] brcmfmac: brcmf_sdio_htclk: HT Avail timeout (1000000): clkctl 0x50
[ 10.263231] brcmfmac: brcmf_sdio_htclk: HT Avail timeout (1000000): clkctl 0x50
[ 10.526658] nf_conntrack version 0.5.0 (16384 buckets, 65536 max)
[ 10.882171] Netfilter messages via NETLINK v0.30.
[ 11.070751] libphy: PHY stmmac-0:ffffffff not found
[ 11.075720] eth0: Could not attach to PHY
[ 11.079880] stmmac_open: Cannot attach to PHY (error: -19)
')
Any hints?