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

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Message-ID: <8f1454ca-4610-03d0-82c4-06174083d463@gmail.com>
Date:   Thu, 4 Jul 2019 12:43:18 -0400
From:   Jes Sorensen <jes.sorensen@...il.com>
To:     Chris Chiu <chiu@...lessm.com>, kvalo@...eaurora.org,
        davem@...emloft.net
Cc:     linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux@...lessm.com
Subject: Re: [PATCH v2] rtl8xxxu: Fix wifi low signal strength issue of
 RTL8723BU

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?

We may need to put in place some code to detect whether we have normal
or inverse configuration of the dongle otherwise?

I really appreciate you're digging into this!

Cheers,
Jes