Re: [PATCH v2 ath-next 2/2] wifi: ath11k: fix HTC rx insufficient length

[Jeff Johnson <jeff.johnson@oss.qualcomm.com>]

On 3/11/2025 1:29 AM, Miaoqing Pan wrote:
> On 3/10/2025 6:09 PM, Johan Hovold wrote:
>> I'm still waiting for feedback from one user that can reproduce the
>> ring-buffer corruption very easily, but another user mentioned seeing
>> multiple zero-length descriptor warnings over the weekend when running
>> with this patch:
>>
>> 	ath11k_pci 0006:01:00.0: rxed invalid length (nbytes 0, max 2048)
>>
>> Are there ever any valid reasons for seeing a zero-length descriptor
>> (i.e. unrelated to the race at hand)? IIUC the warning would only be
>> printed when processing such descriptors a second time (i.e. when
>> is_desc_len0 is set).
>>
> 
> That's exactly the logic, only can see the warning in a second time. For 
> the first time, ath12k_ce_completed_recv_next() returns '-EIO'.

That didn't answer Johan's first question:
Are there ever any valid reasons for seeing a zero-length descriptor?

We have an issue that there is a race condition where hardware updates the
pointer before it has filled all the data. The current solution is just to
read the data a second time. But if that second read also occurs before
hardware has updated the data, then the issue isn't fixed.

So should there be some forced delay before we read a second time?
Or should we attempt to read more times?