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From:   Chris Chiu <chiu@endlessm.com>
Date:   Tue, 29 Jan 2019 17:56:20 +0800
Message-ID: <CAB4CAwd2WtWwf9p=kZZQ-SzE6DhsLu1OpGaVyS1Mq8wx8eT6ww@mail.gmail.com>
Subject: Re: RTL8723bu: poor signal and connection troubles
To:     Carlo Caione <carlo@endlessm.com>
Cc:     Jes Sorensen <jes.sorensen@gmail.com>,
        Barry Day <briselec@gmail.com>, kvalo@codeaurora.org,
        linux-wireless@vger.kernel.org,
        mylene.josserand@free-electrons.com,
        Linux Upstreaming Team <linux@endlessm.com>
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On Mon, Jan 22, 2018 at 6:56 AM Carlo Caione <carlo@endlessm.com> wrote:
>
> On Sun, Jan 21, 2018 at 9:46 PM, Jes Sorensen <jes.sorensen@gmail.com> wrote:
> > On 01/11/2018 05:30 AM, Barry Day wrote:
>
> > One issue with rtl8723bu is that it needs to coexist with the bluetooth
> > driver. When I wrote the rtl8723bu support that was no BT support for
> > the chip in the kernel and it worked fine, at least for me. However if
> > you load the BT driver for the dongle which someone pushed into the
> > kernel since then, it is likely to hijack the antennas causing the weak
> > signal you describe.
>
> Yeah, that's why when testing the dongle I carefully disabled BT and
> made sure no BT driver was probed at all. Still I can see the issue.
> I honestly doubt that the problem is caused by BT coexistence. Any
> other idea or suggestion to debug this problem?
>
> Thanks,
>
> --
> Carlo Caione  |  +44.7384.69.16.04  |  Endless

This problem has been reported for 1 year, but it still persists now.

I found that the problem disappeared after I resume from suspend. Before
suspend, the rssi observed from AP side for this dongle is quite poor. But
it comes back to normal after resume. The signal strength differs almost
30dBm. So I compared/checked the RF/BB related register values
(in .init_phy_bb/.init_phy_rf/.set_tx_power) but they are identical with the
same routines in the driver from https://github.com/lwfinger/rtl8723bu

The registers also remain the same across suspend/resume. Don't really
know why a simple suspend/resume could cause such difference. Can
anyone suggest which part I should look into to get more information?

Chris