hi.
from the many previous posts I was able to decipher the procedure to use:
1) find in the windows driver .inf the hex file to use and convert
2) get and compile and use hex2hcd to convert file to firmware
3) place the file in /lib/firmware/bcrm/BCM43142A0-0a5c-21d7.hcd

and get in my /var/log/syslog, the line that says that the firmware is loaded
Nov  9 20:24:19 callisto kernel: [   23.061550] Bluetooth: hci0: BCM: firmware hci_ver=06 hci_rev=00b0 lmp_ver=06 lmp_subver=210b

until I found out some weeks later than, the firmware is not always loaded when I boot, I don't know why. there is no error in the log but the firmware is not loaded.

If I close the lid and reopen it to hibernate and wake-up then the firmware is finally loaded !

but then I found out the lines
Nov 18 17:04:45 callisto kernel: [ 1769.978201] CPU: 0 PID: 5317 Comm: kworker/u17:0 Tainted: P           OE 3.16.0-24-generic #32-Ubuntu
Nov 18 17:04:45 callisto kernel: [ 1769.978202] Hardware name: Dell Inc. Inspiron 3521/06RYX8, BIOS A12 10/25/2013
Nov 18 17:04:45 callisto kernel: [ 1769.978216] Workqueue: hci0 hci_power_on [bluetooth]
Nov 18 17:04:45 callisto kernel: [ 1769.978219]  0000000000000009 ffff88020b097be8 ffffffff8177fcbc 0000000000000000
Nov 18 17:04:45 callisto kernel: [ 1769.978221]  ffff88020b097c20 ffffffff8106fd8d ffff88020b097d10 ffff880092794920
Nov 18 17:04:45 callisto kernel: [ 1769.978223]  ffff8802348bbb40 00000000fffffff5 0000000000000220 ffff88020b097c30
Nov 18 17:04:45 callisto kernel: [ 1769.978223] Call Trace:
Nov 18 17:04:45 callisto kernel: [ 1769.978229]  [<ffffffff8177fcbc>] dump_stack+0x45/0x56
Nov 18 17:04:45 callisto kernel: [ 1769.978232]  [<ffffffff8106fd8d>] warn_slowpath_common+0x7d/0xa0
Nov 18 17:04:45 callisto kernel: [ 1769.978235]  [<ffffffff8106fe6a>] warn_slowpath_null+0x1a/0x20
Nov 18 17:04:45 callisto kernel: [ 1769.978241]  [<ffffffff814e2be1>] _request_firmware+0x491/0xb20
Nov 18 17:04:45 callisto kernel: [ 1769.978244]  [<ffffffff814e32a1>] request_firmware+0x31/0x50
Nov 18 17:04:45 callisto kernel: [ 1769.978249]  [<ffffffffc057a923>] btusb_setup_bcm_patchram+0x83/0x450 [btusb]
Nov 18 17:04:45 callisto kernel: [ 1769.978252]  [<ffffffff814d9b86>] ? rpm_idle+0xd6/0x2b0
Nov 18 17:04:45 callisto kernel: [ 1769.978264]  [<ffffffffc04d3145>] hci_dev_do_open+0x235/0x930 [bluetooth]
Nov 18 17:04:45 callisto kernel: [ 1769.978268]  [<ffffffff810a26e9>] ? ttwu_do_wakeup+0x19/0xd0
Nov 18 17:04:45 callisto kernel: [ 1769.978278]  [<ffffffffc04d3e20>] hci_power_on+0x40/0x180 [bluetooth]
Nov 18 17:04:45 callisto kernel: [ 1769.978282]  [<ffffffff810a52ff>] ? try_to_wake_up+0x1ff/0x370
Nov 18 17:04:45 callisto kernel: [ 1769.978286]  [<ffffffff8108d8e2>] process_one_work+0x182/0x4e0
Nov 18 17:04:45 callisto kernel: [ 1769.978289]  [<ffffffff8108dcab>] worker_thread+0x6b/0x6a0
Nov 18 17:04:45 callisto kernel: [ 1769.978292]  [<ffffffff8108dc40>] ? process_one_work+0x4e0/0x4e0
Nov 18 17:04:45 callisto kernel: [ 1769.978296]  [<ffffffff81094aeb>] kthread+0xdb/0x100
Nov 18 17:04:45 callisto kernel: [ 1769.978300]  [<ffffffff81094a10>] ? kthread_create_on_node+0x1c0/0x1c0
Nov 18 17:04:45 callisto kernel: [ 1769.978304]  [<ffffffff81787c3c>] ret_from_fork+0x7c/0xb0
Nov 18 17:04:45 callisto kernel: [ 1769.978308]  [<ffffffff81094a10>] ? kthread_create_on_node+0x1c0/0x1c0
Nov 18 17:04:45 callisto kernel: [ 1769.978310] ---[ end trace 9b7c54cc7378b572 ]---
Nov 18 17:04:45 callisto kernel: [ 1769.978312] bluetooth hci0: firmware: brcm/BCM43142A0-0a5c-21d7.hcd will not be loaded
Nov 18 17:04:45 callisto kernel: [ 1769.978315] Bluetooth: hci0: BCM: patch brcm/BCM43142A0-0a5c-21d7.hcd not found

that's kind of confusing. Is it crashing because it tries to reload the firmware whereas it has already been loaded ?

I got that dump stack before installing the firmware, but now the file is there why does it tells it can't find the file ?