linux-kernel - Re: [PATCH v2] rtl8xxxu: Fix wifi low signal strength issue of RTL8723BU

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Date:   Fri, 5 Jul 2019 10:27:03 +0800
From:   Chris Chiu <chiu@...lessm.com>
To:     Jes Sorensen <jes.sorensen@...il.com>
Cc:     Kalle Valo <kvalo@...eaurora.org>,
        David Miller <davem@...emloft.net>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        Linux Upstreaming Team <linux@...lessm.com>
Subject: Re: [PATCH v2] rtl8xxxu: Fix wifi low signal strength issue of RTL8723BU

On Fri, Jul 5, 2019 at 12:43 AM Jes Sorensen <jes.sorensen@...il.com> wrote:
>
> On 7/4/19 6:55 AM, Chris Chiu wrote:
> > The WiFi tx power of RTL8723BU is extremely low after booting. So
> > the WiFi scan gives very limited AP list and it always fails to
> > connect to the selected AP. This module only supports 1x1 antenna
> > and the antenna is switched to bluetooth due to some incorrect
> > register settings.
> >
> > Compare with the vendor driver https://github.com/lwfinger/rtl8723bu,
> > we realized that the 8723bu's enable_rf() does the same thing as
> > rtw_btcoex_HAL_Initialize() in vendor driver. And it by default
> > sets the antenna path to BTC_ANT_PATH_BT which we verified it's
> > the cause of the wifi weak tx power. The vendor driver will set
> > the antenna path to BTC_ANT_PATH_PTA in the consequent btcoexist
> > mechanism, by the function halbtc8723b1ant_PsTdma.
> >
> > This commit hand over the antenna control to PTA(Packet Traffic
> > Arbitration), which compares the weight of bluetooth/wifi traffic
> > then determine whether to continue current wifi traffic or not.
> > After PTA take control, The wifi signal will be back to normal and
> > the bluetooth scan can also work at the same time. However, the
> > btcoexist still needs to be handled under different circumstances.
> > If there's a BT connection established, the wifi still fails to
> > connect until BT disconnected.
> >
> > Signed-off-by: Chris Chiu <chiu@...lessm.com>
> > ---
> >
> >
> > Note:
> >  v2:
> >   - Replace BIT(11) with the descriptive definition
> >   - Meaningful comment for the REG_S0S1_PATH_SWITCH setting
> >
> >
> >  drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_8723b.c | 11 ++++++++---
> >  drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_core.c  |  3 ++-
> >  2 files changed, 10 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_8723b.c b/drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_8723b.c
> > index 3adb1d3d47ac..ceffe05bd65b 100644
> > --- a/drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_8723b.c
> > +++ b/drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_8723b.c
> > @@ -1525,7 +1525,7 @@ static void rtl8723b_enable_rf(struct rtl8xxxu_priv *priv)
> >       /*
> >        * WLAN action by PTA
> >        */
> > -     rtl8xxxu_write8(priv, REG_WLAN_ACT_CONTROL_8723B, 0x04);
> > +     rtl8xxxu_write8(priv, REG_WLAN_ACT_CONTROL_8723B, 0x0c);
> >
> >       /*
> >        * BT select S0/S1 controlled by WiFi
> > @@ -1568,9 +1568,14 @@ static void rtl8723b_enable_rf(struct rtl8xxxu_priv *priv)
> >       rtl8xxxu_gen2_h2c_cmd(priv, &h2c, sizeof(h2c.ant_sel_rsv));
> >
> >       /*
> > -      * 0x280, 0x00, 0x200, 0x80 - not clear
> > +      * Different settings per different antenna position.
> > +      *      Antenna Position:   | Normal   Inverse
> > +      * --------------------------------------------------
> > +      * Antenna switch to BT:    |  0x280,   0x00
> > +      * Antenna switch to WiFi:  |  0x0,     0x280
> > +      * Antenna switch to PTA:   |  0x200,   0x80
> >        */
> > -     rtl8xxxu_write32(priv, REG_S0S1_PATH_SWITCH, 0x00);
> > +     rtl8xxxu_write32(priv, REG_S0S1_PATH_SWITCH, 0x80);
>
> Per the documentation, shouldn't this be set to 0x200 then rather than 0x80?
>
Per the code before REG_S0S1_PATH_SWITCH setting, the driver has told
the co-processor the antenna is inverse.
        memset(&h2c, 0, sizeof(struct h2c_cmd));
        h2c.ant_sel_rsv.cmd = H2C_8723B_ANT_SEL_RSV;
        h2c.ant_sel_rsv.ant_inverse = 1;
        h2c.ant_sel_rsv.int_switch_type = 0;
        rtl8xxxu_gen2_h2c_cmd(priv, &h2c, sizeof(h2c.ant_sel_rsv));

At least the current modification is consistent with the antenna
inverse setting.
I'll verify on vendor driver about when/how the inverse be determined.

Chris

> We may need to put in place so
>
> Cheers,
> Jesme code to detect whether we have normal
> or inverse configuration of the dongle otherwise?
>
> I really appreciate you're digging into this!