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From:   "Mancini, Jason" <Jason.Mancini@amd.com>
To:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: v5.5-rc1 and beyond insta-kills some Comcast wifi routers
Thread-Topic: v5.5-rc1 and beyond insta-kills some Comcast wifi routers
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Date:   Wed, 4 Mar 2020 03:34:09 +0000
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[I can't seem to access the linux-net ml per kernel.org faq, apology=0A=
in advance.]=0A=
=0A=
This change, which I think first appeared for v5.5-rc1, basically=0A=
within seconds, knocks out our [apparently buggy] Comcast wifi for=0A=
about 2-3 minutes.  Is there a boot option (or similar) where I can=0A=
achieve prior kernel behavior?  Otherwise I am stuck on kernel 5.4=0A=
(or Win10) it seems, or forever compiling custom kernels for my=0A=
choice of distribution [as I don't have physical access to the router=0A=
in question.]=0A=
Thanks!=0A=
Jason=0A=
=0A=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=0A=
=0A=
127eef1d46f80056fe9f18406c6eab38778d8a06 is the first bad commit=0A=
commit 127eef1d46f80056fe9f18406c6eab38778d8a06=0A=
Author: Yan-Hsuan Chuang <yhchuang@realtek.com>=0A=
Date:   Wed Oct 2 14:35:23 2019 +0800=0A=
=0A=
    rtw88: add TX-AMSDU support=0A=
=0A=
    Based on the mac80211's TXQ implementation, TX-AMSDU can=0A=
    be used to get higher MAC efficiency. To make mac80211=0A=
    aggregate MSDUs, low level driver just need to leave skbs=0A=
    in the TXQ, and mac80211 will try to aggregate them if=0A=
    possible. As driver will schedule a tasklet when the TX=0A=
    queue is woke, until the tasklet being served, there will=0A=
    have some skbs in the queue if traffic is heavy.=0A=
=0A=
    Driver can control the max AMSDU size depending on the=0A=
    current bit rate used by hardware/firmware. The higher=0A=
    rates are used, the larger AMSDU size can be.=0A=
=0A=
    It is tested that can achieve higher T-Put at higher rates.=0A=
    If the environment is relatively clean, and the bit_rate=0A=
    is high enough, we can get about 80Mbps improvement.=0A=
=0A=
    For lower bit rates, not much gain can we get, so leave=0A=
    the max_amsdu length low to prevent aggregation.=0A=
=0A=
    Signed-off-by: Yan-Hsuan Chuang <yhchuang@realtek.com>=0A=
    Signed-off-by: Kalle Valo <kvalo@codeaurora.org>=0A=
=0A=
 drivers/net/wireless/realtek/rtw88/fw.c   | 24 ++++++++++++++++++++++++=0A=
 drivers/net/wireless/realtek/rtw88/main.c |  1 +=0A=
 2 files changed, 25 insertions(+)=0A=
=0A=
------------------- drivers/net/wireless/realtek/rtw88/fw.c ---------------=
----=0A=
index 4b41bf531998..51649df7cc98 100644=0A=
@@ -29,6 +29,28 @@ static void rtw_fw_c2h_cmd_handle_ext(struct rtw_dev *rt=
wdev,=0A=
        }=0A=
 }=0A=
 =0A=
+static u16 get_max_amsdu_len(u32 bit_rate)=0A=
+{=0A=
+       /* lower than ofdm, do not aggregate */=0A=
+       if (bit_rate < 550)=0A=
+               return 1;=0A=
+=0A=
+       /* lower than 20M 2ss mcs8, make it small */=0A=
+       if (bit_rate < 1800)=0A=
+               return 1200;=0A=
+=0A=
+       /* lower than 40M 2ss mcs9, make it medium */=0A=
+       if (bit_rate < 4000)=0A=
+               return 2600;=0A=
+=0A=
+       /* not yet 80M 2ss mcs8/9, make it twice regular packet size */=0A=
+       if (bit_rate < 7000)=0A=
+               return 3500;=0A=
+=0A=
+       /* unlimited */=0A=
+       return 0;=0A=
+}=0A=
+=0A=
 struct rtw_fw_iter_ra_data {=0A=
        struct rtw_dev *rtwdev;=0A=
        u8 *payload;=0A=
@@ -83,6 +105,8 @@ static void rtw_fw_ra_report_iter(void *data, struct iee=
e80211_sta *sta)=0A=
 =0A=
        si->ra_report.desc_rate =3D rate;=0A=
        si->ra_report.bit_rate =3D bit_rate;=0A=
+=0A=
+       sta->max_rc_amsdu_len =3D get_max_amsdu_len(bit_rate);=0A=
 }=0A=
 =0A=
 static void rtw_fw_ra_report_handle(struct rtw_dev *rtwdev, u8 *payload,=
=0A=
=0A=
------------------ drivers/net/wireless/realtek/rtw88/main.c --------------=
----=0A=
index 690a5c4d64e7..f7044e8bcb5b 100644=0A=
@@ -1310,6 +1310,7 @@ int rtw_register_hw(struct rtw_dev *rtwdev, struct ie=
ee80211_hw *hw)=0A=
        ieee80211_hw_set(hw, SUPPORT_FAST_XMIT);=0A=
        ieee80211_hw_set(hw, SUPPORTS_AMSDU_IN_AMPDU);=0A=
        ieee80211_hw_set(hw, HAS_RATE_CONTROL);=0A=
+       ieee80211_hw_set(hw, TX_AMSDU);=0A=
 =0A=
        hw->wiphy->interface_modes =3D BIT(NL80211_IFTYPE_STATION) |=0A=
                                     BIT(NL80211_IFTYPE_AP) |=