Re: [PATCH RFC 4/8] wifi: ath11k: remove MHI LOOPBACK channels

From: Kalle Valo <kvalo@kernel.org>
To: Jeffrey Hugo <quic_jhugo@quicinc.com>
Cc: Baochen Qiang <quic_bqiang@quicinc.com>,  <mhi@lists.linux.dev>,
	<ath11k@lists.infradead.org>,  <linux-wireless@vger.kernel.org>
Subject: Re: [PATCH RFC 4/8] wifi: ath11k: remove MHI LOOPBACK channels
Date: Mon, 13 Nov 2023 17:04:58 +0200	[thread overview]
Message-ID: <87il65u21x.fsf@kernel.org> (raw)
In-Reply-To: <fb3709a6-95d2-711f-3ca1-0107fa159c62@quicinc.com> (Jeffrey Hugo's message of "Mon, 13 Nov 2023 07:26:46 -0700")

Jeffrey Hugo <quic_jhugo@quicinc.com> writes:

> On 11/13/2023 7:15 AM, Kalle Valo wrote:
>
>> Jeffrey Hugo <quic_jhugo@quicinc.com> writes:
>> 
>>> On 11/11/2023 9:24 PM, Baochen Qiang wrote:
>>>
>>>> On 11/11/2023 12:54 AM, Jeffrey Hugo wrote:
>>>>> On 11/10/2023 3:21 AM, Kalle Valo wrote:
>>>>>> From: Baochen Qiang <quic_bqiang@quicinc.com>
>>>>>>
>>>>>> There is no driver to match these two channels, so
>>>>>> remove them. This fixes warnings from MHI subsystem during suspend:
>>>>>>
>>>>>> mhi mhi0_LOOPBACK: 1: Failed to reset channel, still resetting
>>>>>> mhi mhi0_LOOPBACK: 0: Failed to reset channel, still resetting
>>>>>
>>>>> This feels like just masking a real issue.
>>>>>
>>>>> If LOOPBACK is not being consumed, then the channel should never go
>>>>> into the start state.  Why would we be trying to transition to the
>>>>> reset state then?
>>>>>
>>>>> -Jeff
>>>> That is because, with patch 'bus: mhi: host: add new interfaces to
>>>> handle MHI channels directly' in this patch set, ath11k is able to
>>>> call mhi_unprepare_all_from_transfer(), which will reset all
>>>> channels.
>>>
>>> that implementation is flawed if it is causing this.  Looks like you
>>> never check to see if the channel was prepared in the first place.
>>>
>>> If you go fix that, then it looks like this change is not needed.
>> BTW what do these loopback channels do? I didn't notice any
>> difference
>> in the functionality so I'm wondering the reason for these.
>> 
>
> The loopback channel is defined as a service where any data the host
> sends to the device is immediately sent back to the host, unmodified.
> The typical usecase is smoke test and performance profiling.

Thanks, good to know. We don't have any such functionality in ath11k
right now and if we ever do we can always add the channels back.

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