Received-SPF: pass (google.com: domain of linux-wireless-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <CANgQ54cmG4mCx42i1ErXMJpv=2OmOGjjEgv=8oy90CpKcwkpZg@mail.gmail.com>
 <1615007321.1826.14.camel@realtek.com>
In-Reply-To: <1615007321.1826.14.camel@realtek.com>
From:   =?UTF-8?B?6YKx5ZCN56Kp?= <ccchiu77@gmail.com>
Date:   Mon, 8 Mar 2021 16:46:42 +0800
Message-ID: <CANgQ54dyKk_uoy_VWGxxTZd++5UaC7Tdq48dUzSPdVOE6H8iGQ@mail.gmail.com>
Subject: Re: Questions for TX power get/set implementation of realtek WiFi
To:     Pkshih <pkshih@realtek.com>
Cc:     "yhchuang@realtek.com" <yhchuang@realtek.com>,
        Andy Huang <tehuang@realtek.com>,
        "Larry.Finger@lwfinger.net" <Larry.Finger@lwfinger.net>,
        "kvalo@codeaurora.org" <kvalo@codeaurora.org>,
        "kuba@kernel.org" <kuba@kernel.org>,
        "reto.schneider@husqvarnagroup.com" 
        <reto.schneider@husqvarnagroup.com>, linux-wireless@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

Pkshih <pkshih@realtek.com> =E6=96=BC 2021=E5=B9=B43=E6=9C=886=E6=97=A5 =E9=
=80=B1=E5=85=AD =E4=B8=8B=E5=8D=881:09=E5=AF=AB=E9=81=93=EF=BC=9A
>
> On Tue, 2021-03-02 at 10:21 +0000, =E9=82=B1=E5=90=8D=E7=A2=A9 wrote:
> > Hi guys,
> >     I'm planning to implement the get_txpower hook function of the
> > struct ieee80211_ops and handle the IEEE80211_CONF_CHANGE_POWER for
> > rtl8xxxu driver. So that users can get the information of the current
> > tx power limit and set a new limit value with iw commands.
> >
> >     I found there's phy_txpwr_idx_to_dbm() of each driver in
> > realtek/rtlwifi to translate the tx power index parsed from efuse to
> > tx power level in dBm. Does the power level translated represent the
> > current tx power limit in dBm? In my RTL8188CUS module, the power
> > index of CCK/OFDM from efuse for each channel is basically 36/38, thus
> > the translated txpower level is 11dBm. Is this the expected value for
> > the default txpower limit value? Or do I need some other formula to
> > compute?
>
> Basically, you can use a linear equation to translate power level in dBm =
to
> tx power index written to hardware registers.
>   y =3D ax + b
> where,
>   y: tx power index written to registers
>   x: tx power level in dBm
>   a: a constant, 2
>   b: a constant induced by the value programmed in efuse that is used to
>      adapt modules differences of RF characters.
>
Thanks so much. So it means that the txpwr_idx_to_dbm and dbm_to_idx
functions in rtlwifi family driver are basically correct. Except they
use the constant
b -7 for CCK and -8 for OFDM instead of the value in efuse. I should have
this value from efuse.

> >
> >     And for the handler of IEEE80211_CONF_CHANGE_POWER, can I
> > translate the hw->conf.power_level with the phy_dbm_to_txpwr_idx
> > functions I found in some rtlwifi family drivers, then directly set
> > the txpower index with phy_set_txpower_index functions which write
> > power index to bbreg for different rates (CCK and OFDM)? Are there
> > some invalid values I should take care of because the TCP RX
> > performance seems to be extremely low when I write the power index
> > value translated from 20dBm to bbreg. Any suggestions for what I
> > should handle before writing the bbreg?
>
> The power level you're going to set must be less or equal to original
> one, because it's the hard limit of hardware capability. If the power
> level is too large, the receiver can't understand the signal. Then,
> they can't exchange data that leads low performance as you see.
> I think the performance would be okay if you connect to a near AP and
> power level 10dBm is adapted.
>

Thanks for clarification. So the power index from efuse is basically the
hard limit of the tx power for each channel (and rate)? That explains
my performance issue while I override it with higher value. Thanks

Chris
>
> ---
> Ping-Ke
>