Relevant syslog entries:
Aug 29 19:03:28 raspberrypi kernel: [15488.513857] brcmfmac: brcmf_sdio_hostmail: Unknown mailbox data content: 0x40012
Aug 29 19:04:24 raspberrypi kernel: [15544.105452] brcmfmac: brcmf_proto_bcdc_query_dcmd: brcmf_proto_bcdc_msg failed w/status -110
Aug 29 19:04:24 raspberrypi kernel: [15544.105464] brcmfmac: brcmf_cfg80211_get_tx_power: error (-110)
Aug 29 19:04:46 raspberrypi kernel: [15566.825602] brcmfmac: brcmf_proto_bcdc_query_dcmd: brcmf_proto_bcdc_msg failed w/status -110
Aug 29 19:04:49 raspberrypi kernel: [15569.385624] brcmfmac: brcmf_proto_bcdc_query_dcmd: brcmf_proto_bcdc_msg failed w/status -110
Aug 29 19:04:49 raspberrypi kernel: [15569.385649] brcmfmac: brcmf_cfg80211_get_station: GET STA INFO failed, -110
Aug 29 19:05:24 raspberrypi kernel: [15604.265847] brcmfmac: brcmf_proto_bcdc_query_dcmd: brcmf_proto_bcdc_msg failed w/status -110
Aug 29 19:05:24 raspberrypi kernel: [15604.265860] brcmfmac: brcmf_cfg80211_get_tx_power: error (-110)
Aug 29 19:05:34 raspberrypi kernel: [15614.105922] brcmfmac: brcmf_cfg80211_del_station: SCB_DEAUTHENTICATE_FOR_REASON failed -110
Aug 29 19:05:36 raspberrypi kernel: [15616.665965] brcmfmac: brcmf_cfg80211_change_station: Setting SCB (de-)authorize failed, -110
Aug 29 19:05:39 raspberrypi kernel: [15619.225967] brcmfmac: brcmf_cfg80211_del_station: SCB_DEAUTHENTICATE_FOR_REASON failed -110
Aug 29 19:05:41 raspberrypi kernel: [15621.786004] brcmfmac: brcmf_cfg80211_change_station: Setting SCB (de-)authorize failed, -110
Aug 29 19:05:44 raspberrypi kernel: [15624.346018] brcmfmac: brcmf_cfg80211_del_station: SCB_DEAUTHENTICATE_FOR_REASON failed -110
Aug 29 19:05:47 raspberrypi kernel: [15626.906005] brcmfmac: brcmf_cfg80211_change_station: Setting SCB (de-)authorize failed, -110
Aug 29 19:05:49 raspberrypi kernel: [15629.466045] brcmfmac: brcmf_cfg80211_del_station: SCB_DEAUTHENTICATE_FOR_REASON failed -110
Aug 29 19:05:52 raspberrypi kernel: [15632.026059] brcmfmac: brcmf_cfg80211_change_station: Setting SCB (de-)authorize failed, -110
Aug 29 19:05:54 raspberrypi kernel: [15634.586086] brcmfmac: brcmf_cfg80211_del_station: SCB_DEAUTHENTICATE_FOR_REASON failed -110
Aug 29 19:05:57 raspberrypi kernel: [15637.146073] brcmfmac: brcmf_cfg80211_change_station: Setting SCB (de-)authorize failed, -110
Aug 29 19:05:58 raspberrypi kernel: [15638.106092] brcmfmac: brcmf_netdev_wait_pend8021x: Timed out waiting for no pending 802.1x packets
Aug 29 19:06:00 raspberrypi kernel: [15640.666118] brcmfmac: send_key_to_dongle: wsec_key error (-110)
Aug 29 19:06:03 raspberrypi kernel: [15643.226160] brcmfmac: brcmf_cfg80211_del_station: SCB_DEAUTHENTICATE_FOR_REASON failed -110
Aug 29 19:06:05 raspberrypi kernel: [15645.786163] brcmfmac: brcmf_cfg80211_change_station: Setting SCB (de-)authorize failed, -110
Aug 29 19:06:08 raspberrypi kernel: [15648.346197] brcmfmac: brcmf_cfg80211_del_station: SCB_DEAUTHENTICATE_FOR_REASON failed -110
Aug 29 19:06:11 raspberrypi kernel: [15650.906191] brcmfmac: brcmf_cfg80211_del_station: SCB_DEAUTHENTICATE_FOR_REASON failed -110

root@raspberrypi:/home/pi# cat /sys/kernel/debug/brcmfmac/mmc1\:0001\:1/console_interval
10
root@raspberrypi:/home/pi# cat /sys/kernel/debug/brcmfmac/mmc1\:0001\:1/counters
intrcount:    755860
lastintrs:    0
pollcnt:      0
regfails:     0
tx_sderrs:    0
fcqueued:     916764
rxrtx:        0
rx_toolong:   0
rxc_errors:   0
rx_hdrfail:   0
rx_badhdr:    0
rx_badseq:    24
fc_rcvd:      476
fc_xoff:      238
fc_xon:       238
rxglomfail:   0
rxglomframes: 13848
rxglompkts:   33686
f2rxhdrs:     1544121
f2rxdata:     828252
f2txdata:     538569
f1regdata:    1511726
tickcnt:      172213
tx_ctlerrs:   46
tx_ctlpkts:   1214
rx_ctlerrs:   0
rx_ctlpkts:   1214
rx_readahead: 0
root@raspberrypi:/home/pi# cat /sys/kernel/debug/brcmfmac/mmc1\:0001\:1/features
Features: 000000d6
	MCHAN
	PNO
	P2P
	TDLS
	SCAN_RANDOM_MAC

Quirks:   00000000

root@raspberrypi:/home/pi# cat /sys/kernel/debug/brcmfmac/mmc1\:0001\:1/forensics
dongle trap info: type 0x3 @ epc 0x0000c072
  cpsr 0x60000003 spsr 0x61000010 sp 0x0006fe94
  lr   0x0000c02f pc   0x0000c072 offset 0x6fe40
  r0   0x00000003 r1   0x00fe961e r2 0x00000000 r3 0x000001f0
  r4   0x00054948 r5   0x18001000 r6 0x0006ad6c r7 0x00000040
at 0x00af m_cts_duration 0x0000 m_ucode_dbgst 0x0002
015485.126      wepctl 0x0350, pcmctl 0x0300, pcmstat 0x0000
015485.126 M_RXFRM_BLK scr(0:63) btc_params(0:63) PC AXI slave error; APB Bridge 0
015485.126 	 errlog: lo 0x180013fe, hi 0x00000000, id 0x00040004, flags 0x00000100, status 0x00000005
015485.126
FWID 01-f8a78378
flags 1
015485.126
TRAP 3(6fe40): pc c072, lr c02f, sp 6fe94, cpsr 60000003, spsr 61000010
015485.127   r0 3, r1 fe961e, r2 0, r3 1f0, r4 54948, r5 18001000, r6 6ad6c
015485.127   r7 40, r8 549c8, r9 6ff40, r10 18004000, r11 18104000, r12 0
015485.127
   sp+0 00000003 00fe961e 00000000 000001f0
015485.127   sp+10 00000000 0000c02f 0000c072 61000010

015485.127 sp+14 0000c02f
015485.127 sp+4c 0000c0b5
015485.127 sp+68 00000413
015485.127 sp+6c 0000c12f
015485.127 sp+7c 00020b31
015485.127 sp+a4 00007eb5
015485.127 sp+c4 000027d1
015485.127 sp+d4 00002efd
015485.127 sp+dc 000020d1
015485.127 sp+128 00002ab3
015485.127 sp+148 00002ab3

root@raspberrypi:/home/pi# cat /sys/kernel/debug/brcmfmac/mmc1\:0001\:1/revinfo
vendorid: 0x14e4
deviceid: 0x43e2
radiorev: 0.61.160
chipnum: 43430 (a9a6)
chiprev: 1
chippkg: 4
corerev: 39
boardid: 0x0726
boardvendor: 0x14e4
boardrev: P101
driverrev: 7.45.41.46
ucoderev: 0
bus: 0
phytype: 12
phyrev: 0
anarev: 0
nvramrev: 00000000

root@raspberrypi:/home/pi# uname -a
Linux raspberrypi 4.9.45-v7+ #1031 SMP Fri Aug 25 19:02:16 BST 2017 armv7l GNU/Linux