linux-kernel - Re: [PATCH] Revert "Revert "wifi: ath11k: Enable threaded NAPI""

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Date:   Thu, 10 Aug 2023 10:03:55 +0530
From:   Manikanta Pubbisetty <quic_mpubbise@...cinc.com>
To:     Johan Hovold <johan@...nel.org>
CC:     Johan Hovold <johan+linaro@...nel.org>,
        Kalle Valo <kvalo@...nel.org>,
        Jeff Johnson <quic_jjohnson@...cinc.com>,
        Bjorn Andersson <quic_bjorande@...cinc.com>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        <ath11k@...ts.infradead.org>, <linux-wireless@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Revert "Revert "wifi: ath11k: Enable threaded NAPI""

On 8/9/2023 2:46 PM, Johan Hovold wrote:
> On Wed, Aug 09, 2023 at 02:32:37PM +0530, Manikanta Pubbisetty wrote:
>> On 8/9/2023 1:04 PM, Johan Hovold wrote:
>>> This reverts commit d265ebe41c911314bd273c218a37088835959fa1.
>>>
>>> Disabling threaded NAPI causes the Lenovo ThinkPad X13s to hang (e.g. no
>>> more interrupts received) almost immediately during RX.
>>>
>>> Apparently something broke since commit 13aa2fb692d3 ("wifi: ath11k:
>>> Enable threaded NAPI") so that a simple revert is no longer possible.
>>>
>>
>> This is getting as weird as it would get :)
>>
>>> As commit d265ebe41c91 ("Revert "wifi: ath11k: Enable threaded NAPI"")
>>> does not address the underlying issue reported with QCN9074, it seems we
>>> need to reenable threaded NAPI before fixing both bugs properly.
>>>
>>
>> It seems that the revert has actually solved the issue reported with
>> QCN9074.
>>
>> https://bugzilla.kernel.org/show_bug.cgi?id=217536
> 
> Sure, but it's only a workaround as the underlying cause has not been
> identified.
> 
>> We were trying to reproduce the problem on X86+QCN9074 (with threaded
>> NAPI) from quite some time, but there is no repro yet.
>>
>> Actually, enabling/disabling threaded NAPI is a simple affair; I'm
>> wondering to hear that interrupts are blocked due  to not having
>> threaded NAPI.
> 
> It sounds to me like the driver's locking is broken if moving to softirq
> processing hangs the machine like this. But I have not had time to try
> to try to track it down besides verifying that reenabling threaded NAPI
> makes the problem go away.
> 
>> What is the chip that Lenovo Thinkpad X13s is having?
> 
> It's a WCN6855 (QCNFA765).
> 

WCN6855 & QCN9074 share the same driver code base since both being PCIe 
devices. One working and another not working seems to be surprising. Do 
you have a dmesg log when this problem occurred?

We are working on to root cause the original problem. The hindrance as 
of today is that we are not able to repro this so far in Qualcomm. We 
are planning to work with the reporter to get more logs.

Thanks,
Manikanta