Comment 1 for bug 1862760

I'm actually getting good results using the updated brcmfmac43455 firmware files which Raspbian is using. To use them I first removed '/lib/firmware/brcm/brcmfmac43455-sdio.raspberrypi*' then put the brcmfmac43455-sdio* files in the same directory and rebooted.

ubuntu@ubuntu:~$ cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=18.04
DISTRIB_CODENAME=bionic
DISTRIB_DESCRIPTION="Ubuntu 18.04.4 LTS"
ubuntu@ubuntu:~$ ip address show wlan0
3: wlan0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether dc:a6:32:37:37:08 brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.111/24 brd 192.168.1.255 scope global dynamic wlan0
       valid_lft 85747sec preferred_lft 85747sec
    inet6 fe80::dea6:32ff:fe37:3708/64 scope link
       valid_lft forever preferred_lft forever
ubuntu@ubuntu:~$ md5sum /lib/firmware/brcm/brcmfmac43455-sdio.*
963eb0d4903040974ee88b4f85cb1f4f /lib/firmware/brcm/brcmfmac43455-sdio.bin
c5aeca0e33de4ae870986c517963fef7 /lib/firmware/brcm/brcmfmac43455-sdio.clm_blob
7b983812a8aee7bf701460436c686226 /lib/firmware/brcm/brcmfmac43455-sdio.txt
ubuntu@ubuntu:~$ dmesg | grep brcmfmac
[ 12.265990] brcmfmac: F1 signature read @0x18000000=0x15264345
[ 12.271828] brcmfmac: brcmf_fw_alloc_request: using brcm/brcmfmac43455-sdio for chip BCM4345/6
[ 12.284536] usbcore: registered new interface driver brcmfmac
[ 12.355127] brcmfmac mmc1:0001:1: Direct firmware load for brcm/brcmfmac43455-sdio.raspberrypi,4-model-b.txt failed with error -2
[ 12.548549] brcmfmac: brcmf_fw_alloc_request: using brcm/brcmfmac43455-sdio for chip BCM4345/6
[ 12.579186] brcmfmac: brcmf_c_preinit_dcmds: Firmware: BCM4345/6 wl0: Feb 27 2018 03:15:32 version 7.45.154 (r684107 CY) FWID 01-4fbe0b04
[ 13.578117] brcmfmac: power management disabled
ubuntu@ubuntu:~$ iw dev
phy#0
        Unnamed/non-netdev interface
                wdev 0x2
                addr 52:4f:c2:5b:63:7a
                type P2P-device
                txpower 31.00 dBm
        Interface wlan0
                ifindex 3
                wdev 0x1
                addr dc:a6:32:37:37:08
                ssid Linksys01146_5GHz
                type managed
                channel 44 (5220 MHz), width: 80 MHz, center1: 5210 MHz
                txpower 31.00 dBm

For the record I'm connecting to a Linksys EA7450 wireless access point and I've restricted the 5GHz frequency to 802.11ac only.