rtl8723bu: low signal, fails to associate

rtl8723bu: low signal, fails to associate

[James Cameron]

G'day Carlo, Mylene, and James,

Thanks for your earlier reports about RTL8723bu.  Have you any more
recent experiences you might share?

I'm evaluating a sample laptop which worked fine with Windows 10, but
not very well with Ubuntu 18.04, and kernel v4.15 or kernel v4.18.4.

The laptop is by Hena, model NT16-PRO-C-E, with a wireless device on
internal USB (0x0bda:0xb720) which loads rtl8xxxu, identifying as
RTL8723BU.

http://dev.laptop.org/~quozl/z/1ft0qv.txt (dmesg)

Symptoms are low RSSI on scan, very short range, and often a failure
to associate over a distance of two metres in a radio quiet location.

Symptoms began after first power off, which suggests that device
registers programmed by the previous operating system Windows 10 had
not been reset by reboot into the Ubuntu 18.04 installer.  The device
worked fine in Ubuntu 18.04 before the first power off.

Jes, let me know if there is anything I can do to help.

-- 
James Cameron
http://quozl.netrek.org/

Re: rtl8723bu: low signal, fails to associate

[Jes Sorensen]

On 08/23/2018 09:36 PM, James Cameron wrote:
> G'day Carlo, Mylene, and James,
> 
> Thanks for your earlier reports about RTL8723bu.  Have you any more
> recent experiences you might share?
> 
> I'm evaluating a sample laptop which worked fine with Windows 10, but
> not very well with Ubuntu 18.04, and kernel v4.15 or kernel v4.18.4.
> 
> The laptop is by Hena, model NT16-PRO-C-E, with a wireless device on
> internal USB (0x0bda:0xb720) which loads rtl8xxxu, identifying as
> RTL8723BU.
> 
> http://dev.laptop.org/~quozl/z/1ft0qv.txt (dmesg)
> 
> Symptoms are low RSSI on scan, very short range, and often a failure
> to associate over a distance of two metres in a radio quiet location.
> 
> Symptoms began after first power off, which suggests that device
> registers programmed by the previous operating system Windows 10 had
> not been reset by reboot into the Ubuntu 18.04 installer.  The device
> worked fine in Ubuntu 18.04 before the first power off.
> 
> Jes, let me know if there is anything I can do to help.

It's been a while since I had time to look at the 8723bu support, and
rtl8xxxu doesn't have BT coexist support. I notice that your laptop does
load the bluetooth module for 8723bu which I believe fiddles with the
antenna configuration and is likely to take control of the antennas. I
suspect this is why you see low signal quality on the WiFi side.

If you blacklist the BT module, does it work better?

Jes

Re: rtl8723bu: low signal, fails to associate

[James Cameron]

On Wed, Aug 29, 2018 at 04:19:01PM -0400, Jes Sorensen wrote:
> On 08/23/2018 09:36 PM, James Cameron wrote:
> > G'day Carlo, Mylene, and James,
> > 
> > Thanks for your earlier reports about RTL8723bu.  Have you any more
> > recent experiences you might share?
> > 
> > I'm evaluating a sample laptop which worked fine with Windows 10, but
> > not very well with Ubuntu 18.04, and kernel v4.15 or kernel v4.18.4.
> > 
> > The laptop is by Hena, model NT16-PRO-C-E, with a wireless device on
> > internal USB (0x0bda:0xb720) which loads rtl8xxxu, identifying as
> > RTL8723BU.
> > 
> > http://dev.laptop.org/~quozl/z/1ft0qv.txt (dmesg)
> > 
> > Symptoms are low RSSI on scan, very short range, and often a failure
> > to associate over a distance of two metres in a radio quiet location.
> > 
> > Symptoms began after first power off, which suggests that device
> > registers programmed by the previous operating system Windows 10 had
> > not been reset by reboot into the Ubuntu 18.04 installer.  The device
> > worked fine in Ubuntu 18.04 before the first power off.
> > 
> > Jes, let me know if there is anything I can do to help.
> 
> It's been a while since I had time to look at the 8723bu support, and
> rtl8xxxu doesn't have BT coexist support. I notice that your laptop does
> load the bluetooth module for 8723bu which I believe fiddles with the
> antenna configuration and is likely to take control of the antennas. I
> suspect this is why you see low signal quality on the WiFi side.
> 
> If you blacklist the BT module, does it work better?

Thanks.  No, it doesn't work any better, or worse.

Method: add "blacklist btusb" to /etc/modprobe.d/blacklist.conf,
regenerate initramfs, and boot.

Also, a difference in symptom between cold and warm boot;

*  on cold boot after 15 seconds of power off, device connects but has
   short range, with received power at monitor of -76dBm,

   http://dev.laptop.org/~quozl/z/1fv7sW.txt (dmesg, cold boot, no btusb)

*  on warm boot with less than 5 seconds of power off, device does not
   connect, dmesg "authentication with xx:yy:zz:aa:bb:cc timed out",
   and probe request, authentication, and association packets are not
   seen by monitor,

   http://dev.laptop.org/~quozl/z/1fv8IO.txt (dmesg, warm boot, no btusb)

In both cases, scan results are normal, and similar signal level.  An
active scan for cold boot, and a passive scan for warm boot.

Monitor device is an ath9k about 30cm away; a radio quiet environment
on a farm.

Speculation; device registers are not being reset.  Would not have
been a problem for RTL8723BU on removable USB.

-- 
James Cameron
http://quozl.netrek.org/