MIME-Version: 1.0
References: <CAL9uMOFT3VwqHs5+wvot+dxArvhd7Bi-U5+CKhYUXjYwHcU=jg@mail.gmail.com>
 <20180111103006.GA17574@thinktank.home.org> <14c5f7f4-0d5b-cecd-b45b-3672b67da07a@gmail.com>
 <CAL9uMOG77it=kqkbjryPVpY2eVJqqjedVeAhdxqpZM6Z8JWuiA@mail.gmail.com> <CAB4CAwd2WtWwf9p=kZZQ-SzE6DhsLu1OpGaVyS1Mq8wx8eT6ww@mail.gmail.com>
In-Reply-To: <CAB4CAwd2WtWwf9p=kZZQ-SzE6DhsLu1OpGaVyS1Mq8wx8eT6ww@mail.gmail.com>
From:   Chris Chiu <chiu@endlessm.com>
Date:   Tue, 12 Feb 2019 23:38:44 +0800
Message-ID: <CAB4CAwdkYSJBLODnS2_vgps8Ds+vhedSDVVRATMAz3OGhW_5=Q@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>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-wireless-owner@vger.kernel.org
Precedence: bulk

On Tue, Jan 29, 2019 at 5:56 PM Chris Chiu <chiu@endlessm.com> wrote:
>
> 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

I found one thing interesting. It does seem to be related to BT coexist just
as Jes mentioned. Follow the steps below and the signal can always come
back to normal. The '1-7:1.0' is one of the IDs for the rtl8723bu usb interface.

1. unbind btusb first, cd /sys/bus/usb/drivers/btusb; echo 1-7:1.0 > unbind
2. unload rtl8xxxu driver then reload it. The signal stays at poor level
3. bind the btusb. cd /sys/bus/usb/drivers/btusb; echo 1-7:1.0 > bind

Seems that the BT firmware loaded is helpful for the only antenna config
which is shared by WiFi/BT. If I load the BT firmware after rtl8xxxu driver,
everything's fine.

Can anyone suggest the next step? I've compared all registers and h2c cmds
between vendor driver and rtl8xxxu driver. Basically, they're almost the same
even the bt coexist related settings. So it's difficult to imagine why the same
power on sequence setting and RF enable setting cause that huge signal
difference.

Chris