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Subject: Re: rtl8821ae dbi read question
To: Nik Nyby <nikolas@gnu.org>, linux-wireless@vger.kernel.org,
        pkshih@realtek.com
References: <d46763ef-14d1-a6fa-fb33-a0bd676ef056@gnu.org>
 <695fe947-7b0d-ef4b-5e90-ff503df6a08b@lwfinger.net>
 <6155a30b-ca6d-e27d-701e-9e1876a982ff@gnu.org>
From: Larry Finger <Larry.Finger@lwfinger.net>
Message-ID: <e1833699-e76c-7457-258d-3d2401af9fb4@lwfinger.net> (sfid-20171106_024703_474533_BA9BC868)
Date: Sun, 5 Nov 2017 19:46:56 -0600
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On 11/05/2017 02:53 PM, Nik Nyby wrote:
> On 11/05/2017 11:50 AM, Larry Finger wrote:
>>
>> If you read the commit message for commit b8b8b16352cd, you will find that we 
>> do not understand why using a byte read causes failure, but reverting the 
>> change so that it is a word read made it function again. The "fix" was found 
>> by a user doing bisection, and verified on my system, where the RTL8821AE has 
>> stable connections. The transfer rates take wild swings, but the connection is 
>> not dropped.
>>
>> If you NIC behaves differently, then you will need to help us debug the 
>> problem. If you had a kernel that worked, then you might try bisection. 
> 
> I just tested on kernels 4.12 and 4.13 - my connection gets dropped on those 
> kernels as well. Right now I'm using 4.14-rc7.
> 
>> If that is not possible, you might try various combinations of module 
>> parameters aspm, int_clear, and msi
> Thanks for these suggestions. Disabling ASPM solves my connection dropping 
> issue! Previously, I was getting disconnected around 10 seconds after starting 
> "git clone" on a large git repository. Now, I haven't seen the connection drop 
> once.
> 
> I can help debug the issue. I'm using a Lenovo Ideapad 320-15ABR laptop. Here's 
> the lspci -vv info for my NIC:
> 
> 01:00.0 Network controller: Realtek Semiconductor Co., Ltd. RTL8821AE 802.11ac 
> PCIe Wireless Network Adapter
>          Subsystem: Lenovo RTL8821AE 802.11ac PCIe Wireless Network Adapter
>          Control: I/O+ Mem+ BusMaster+ SpecCycle- MemWINV- VGASnoop- ParErr- 
> Stepping- SERR- FastB2B- DisINTx+
>          Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- 
> <MAbort- >SERR- <PERR- INTx-
>          Latency: 0, Cache Line Size: 32 bytes
>          Interrupt: pin A routed to IRQ 33
>          Region 0: I/O ports at 2000 [size=256]
>          Region 2: Memory at f0b00000 (64-bit, non-prefetchable) [size=16K]
>          Capabilities: <access denied>
>          Kernel driver in use: rtl8821ae

If "aspm=0" fixes your issue, then there is nothing more to debug. That option 
is there to handle cases where the PCI connection does not behave the way that 
most do. This condition seems to be most common on Lenovo machines. Frequently, 
ASPM problems are accompanied by PCI errors, but that seems not to be the case 
for your machine. Create a suitable .conf file in /etc/modprobe.d/ and you 
should be OK.

Larry