On Kingfisher board, onboard bluetooth does not reliably, or does not work at all.

Very often, the bluetooth controller is not listed at all.

Several reboots are required to have it working. Keeping the board powered off for a while seems to help a little.

When it works, connecting to paired device (within bluetoothctl) can fail after some disconnect/reconnect actions, and the only way to recover it a board reboot.

It is worth to notice that the filesystem is missing a requested firmware:

[ 13.176181] wl18xx_driver wl18xx.4.auto: Direct firmware load for ti-connectivity/wl18xx-conf.bin failed with error -2
[ 13.190490] wlcore: ERROR could not get configuration binary ti-connectivity/wl18xx-conf.bin: -2

[ 13.199476] wlcore: WARNING falling back to default config
[ 13.625468] wlcore: wl18xx HW: 183x or 180x, PG 2.2 (ROM 0x11)
[ 13.639641] wlcore: WARNING Detected unconfigured mac address in nvs, derive from fuse instead.

[ 13.649837] wlcore: WARNING This default nvs file can be removed from the file system

---------

From time to time, there are other kernel errors like this at boot time:

[ 24.650893] -----------[ cut here ]-----------
[ 24.655535] WARNING: CPU: 0 PID: 0 at /kernel-source//drivers/dma/sh/rcar-dmac.c:343 rcar_dmac_chan_start_xfer+0x1c0/0x1c8
[ 24.666570] Modules linked in: can_bcm can 8021q garp stp mrp llc bnep nfc arc4 wl18xx wlcore mac80211 cfg80211 pvrsrvkm(O) crc32_ce crct10dif_ce btwilink wlcore_sdio rcar_can bluetooth can_dev st_drv ecdh_generic rfkill vspm_if(O) vsp2(O) vspm(O) uvcs_drv(O) mmngrbuf(O) mmngr(O)
[ 24.691390] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G O 4.14.0-yocto-standard #3
[ 24.699821] Hardware name: Renesas M3ULCB Kingfisher board based on r8a7796 (DT)
[ 24.707210] task: ffff0000091c2400 task.stack: ffff0000091b0000
[ 24.713125] PC is at rcar_dmac_chan_start_xfer+0x1c0/0x1c8
[ 24.718605] LR is at rcar_dmac_chan_start_xfer+0x20/0x1c8
[ 24.723997] pc : [<ffff000008515ff8>] lr : [<ffff000008515e58>] pstate: 000001c5
[ 24.731384] sp : ffff000008003d80
[ 24.734691] x29: ffff000008003d80 x28: ffff0000091c2400
[ 24.739998] x27: 0000000000000001 x26: 0000000000000004
[ 24.745305] x25: 0000000000000061 x24: 0000000000000001
[ 24.750612] x23: ffff00000858f1f8 x22: ffff000009333f0c
[ 24.755918] x21: ffff000009333f60 x20: ffff8005fcc9c43c
[ 24.761225] x19: ffff8005fcc9c390 x18: 0000000000000000
[ 24.766531] x17: 0000ffff9911f000 x16: 0000ffff99586f98
[ 24.771837] x15: 0000000000000000 x14: 0000000000000400
[ 24.777143] x13: 0000000000000400 x12: 0000000000000000
[ 24.782449] x11: 0000000000000001 x10: 0000000000000040
[ 24.787755] x9 : ffff0000091d2e60 x8 : ffff8005fd400248
[ 24.793062] x7 : ffff8005fd400270 x6 : 0000000000000000
[ 24.798368] x5 : ffff8005f26c5148 x4 : 0000000000004800
[ 24.803674] x3 : ffff8005f26c50d8 x2 : ffff8005fcc9c390
[ 24.808981] x1 : 000000000000000c x0 : 0000000000004801
[ 24.814287] Call trace:
[ 24.816728] Exception stack(0xffff000008003c40 to 0xffff000008003d80)
[ 24.823163] 3c40: 0000000000004801 000000000000000c ffff8005fcc9c390 ffff8005f26c50d8
[ 24.830985] 3c60: 0000000000004800 ffff8005f26c5148 0000000000000000 ffff8005fd400270
[ 24.838807] 3c80: ffff8005fd400248 ffff0000091d2e60 0000000000000040 0000000000000001
[ 24.846629] 3ca0: 0000000000000000 0000000000000400 0000000000000400 0000000000000000
[ 24.854452] 3cc0: 0000ffff99586f98 0000ffff9911f000 0000000000000000 ffff8005fcc9c390
[ 24.862273] 3ce0: ffff8005fcc9c43c ffff000009333f60 ffff000009333f0c ffff00000858f1f8
[ 24.870095] 3d00: 0000000000000001 0000000000000061 0000000000000004 0000000000000001
[ 24.877917] 3d20: ffff0000091c2400 ffff000008003d80 ffff000008515e58 ffff000008003d80
[ 24.885739] 3d40: ffff000008515ff8 00000000000001c5 0000000100000100 0000000000000000
[ 24.893560] 3d60: 0001000000000000 ffff8005f27bcee8 ffff000008003d80 ffff000008515ff8
[ 24.901384] [<ffff000008515ff8>] rcar_dmac_chan_start_xfer+0x1c0/0x1c8
[ 24.907905] [<ffff000008516098>] rcar_dmac_issue_pending+0x98/0xb0
[ 24.914085] [<ffff00000858b768>] sci_submit_rx+0xa0/0x110
[ 24.919480] [<ffff00000858ced0>] sci_rx_interrupt+0x70/0x198
[ 24.925133] [<ffff00000858d714>] sci_mpxed_interrupt+0x16c/0x1e8
[ 24.931139] [<ffff00000811b1b4>] __handle_irq_event_percpu+0x5c/0x148
[ 24.937573] [<ffff00000811b2bc>] handle_irq_event_percpu+0x1c/0x58
[ 24.943746] [<ffff00000811b340>] handle_irq_event+0x48/0x78
[ 24.949313] [<ffff00000811f108>] handle_fasteoi_irq+0xa8/0x180
[ 24.955138] [<ffff00000811a2f4>] generic_handle_irq+0x24/0x38
[ 24.960877] [<ffff00000811a974>] __handle_domain_irq+0x5c/0xb8
[ 24.966705] [<ffff000008081670>] gic_handle_irq+0x58/0xa8
[ 24.972096] Exception stack(0xffff0000091b3dd0 to 0xffff0000091b3f10)
[ 24.978528] 3dc0: 0000000000000000 0000000000000000
[ 24.986350] 3de0: 0000000000000001 0000000000000000 0000000000000000 ffff0000091b3f10
[ 24.994172] 3e00: 00008005f6d50000 0000000000000001 0000000000000002 ffff0000091b3e90
[ 25.001993] 3e20: 0000000000000a00 0000000000000001 0000000000000000 0000000000000400
[ 25.009815] 3e40: 0000000000000400 0000000000000000 0000ffff99586f98 0000ffff9911f000
[ 25.017637] 3e60: 0000000000000000 ffff00000919f000 ffff0000091b9000 ffff0000091b9000
[ 25.025459] 3e80: ffff0000091aa560 ffff0000091b9e90 0000000000000000 0000000000000000
[ 25.033281] 3ea0: ffff0000091c2400 0000000000000000 0000000049090018 ffff0000091b3f10
[ 25.041103] 3ec0: ffff0000080854e4 ffff0000091b3f10 ffff0000080854e8 0000000000000145
[ 25.048925] 3ee0: 0000000000000000 0000000050001c60 ffffffffffffffff ffff000008140dbc
[ 25.056746] 3f00: ffff0000091b3f10 ffff0000080854e8
[ 25.061616] [<ffff0000080830f0>] el1_irq+0xb0/0x124
[ 25.066489] [<ffff0000080854e8>] arch_cpu_idle+0x10/0x18
[ 25.071795] [<ffff000008105bf8>] do_idle+0x120/0x1e0
[ 25.076753] [<ffff000008105e54>] cpu_startup_entry+0x24/0x28
[ 25.082408] [<ffff000008b49920>] rest_init+0xd0/0xe0
[ 25.087370] [<ffff000009090b70>] start_kernel+0x398/0x3ac
[ 25.092762] --[ end trace 9011977ffbf8fc44 ]--
[ 31.16