linux-kernel - Re: [PATCH] rtl8xxxu: Use lower tx rates for the ack packet

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Date:   Thu, 30 Sep 2021 09:57:58 -0400
From:   Jes Sorensen <jes.sorensen@...il.com>
To:     Chris Chiu <chris.chiu@...onical.com>, kvalo@...eaurora.org,
        davem@...emloft.net, kuba@...nel.org
Cc:     linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rtl8xxxu: Use lower tx rates for the ack packet

On 9/30/21 6:44 AM, Chris Chiu wrote:
> According to the Realtek propritary driver and the rtw88 driver, the
> tx rates of the ack (includes block ack) are initialized with lower
> tx rates (no HT rates) which is set by the RRSR register value. In
> real cases, ack rate higher than current tx rate could lead to
> difficulty for the receiving end to receive management/control frames.
> The retransmission rate would be higher then expected when the driver
> is acting as receiver and the RSSI is not good.
> 
> Cross out higer rates for ack packet before implementing dynamic rrsr
> configuration

Theory of this looks sound to me, but there's an implementation detail,
see below.

> Signed-off-by: Chris Chiu <chris.chiu@...onical.com>
> ---
>  drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_core.c | 7 ++++++-
>  drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_regs.h | 2 ++
>  2 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_core.c b/drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_core.c
> index 774341b0005a..413cccd88f5c 100644
> --- a/drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_core.c
> +++ b/drivers/net/wireless/realtek/rtl8xxxu/rtl8xxxu_core.c
> @@ -4460,13 +4460,18 @@ void rtl8xxxu_gen1_init_aggregation(struct rtl8xxxu_priv *priv)
>  
>  static void rtl8xxxu_set_basic_rates(struct rtl8xxxu_priv *priv, u32 rate_cfg)
>  {
> +	struct ieee80211_hw *hw = priv->hw;
>  	u32 val32;
>  	u8 rate_idx = 0;
>  
>  	rate_cfg &= RESPONSE_RATE_BITMAP_ALL;
>  
>  	val32 = rtl8xxxu_read32(priv, REG_RESPONSE_RATE_SET);
> -	val32 &= ~RESPONSE_RATE_BITMAP_ALL;
> +	       val32 = rtl8xxxu_read32(priv, REG_RESPONSE_RATE_SET);

You're reading REG_RESPONSE_RATE_SET twice.

Cheers,
Jes