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Subject: Re: v5.5-rc1 and beyond insta-kills some Comcast wifi routers
To:     Tony Chuang <yhchuang@realtek.com>,
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From:   Jason Mancini <Jason.Mancini@amd.com>
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Date:   Wed, 4 Mar 2020 23:06:58 -0800
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On 3/4/20 2:41 AM, Tony Chuang wrote:
> Unfortunately, no, there's no flag to turn off this.
> But, from your experiments, if you applied that patch,
> ("rtw88: disable TX-AMSDU on 2.4G band") connect to AP on 2.4G, and still crash
> the Comcast AP, then it looks like it's not TX-AMSDU to be blamed.
>
> Assume the return value you mentioned is max_rc_amsdu_len, if you always
> return 1, it will just disable all of the AMSDU process.
> You can try it, and to see if sending AMSDU will crash the router or not.
>
> Yen-Hsuan

(Specifically, this Comcast router is "Arris TG1682G" firmware 10.1.27B.SIP.PC20.CT hardware version 9.0)

I re-tested tonight, here are the results, from *unpatched* kernels:

(1) 2.4G only w/5G disabled via router control panel: kernel 5.5/5.6 seemingly doesn't upset router.
(2) 5G only w/2.4G disabled via router control panel: kernel 5.5/5.6 definitely kill router wifi.
(3) 5G only w/2.4G disabled via router control panel: plus get_max_amsdu_len forced to return 1: kernel 5.6-rc4 seemingly doesn't upset router.

As you can see, the suggested patch isn't going to help result (2), and apparently isn't needed for (1).  And this router's 5G seems
allergic to amsdu per (3), so somehow amsdu is involved it seems.

Well, I'll just work around it with (3) custom kernels, or (1) leave the router in 2.4G mode.  But be aware that apparently there's at least
one common buggy wifi router that's going to puke on 5G + amsdu.

Jason