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

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Date:   Fri, 5 Jul 2019 14:24:57 -0400
From:   Jes Sorensen <jes.sorensen@...il.com>
To:     Chris Chiu <chiu@...lessm.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 7/4/19 10:27 PM, Chris Chiu wrote:
> 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.

Fair enough :)

Cheers,
Jes