linux-kernel - Re: [PATCH 5/7] dt-bindings: remoteproc: qcom,pas: Add hwlocks

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Date: Wed, 22 May 2024 09:26:00 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Bjorn Andersson <quic_bjorande@...cinc.com>
Cc: Chris Lew <quic_clew@...cinc.com>, Bjorn Andersson
 <andersson@...nel.org>, Baolin Wang <baolin.wang@...ux.alibaba.com>,
 Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Will Deacon <will@...nel.org>, Waiman Long <longman@...hat.com>,
 Boqun Feng <boqun.feng@...il.com>, Jonathan Corbet <corbet@....net>,
 Mathieu Poirier <mathieu.poirier@...aro.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>,
 Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
 Konrad Dybcio <konrad.dybcio@...aro.org>, linux-remoteproc@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
 linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH 5/7] dt-bindings: remoteproc: qcom,pas: Add hwlocks

On 21/05/2024 21:17, Bjorn Andersson wrote:
>>>
>>> Hi Krzysztof,
>>>
>>> Sorry for the confusion, I dont think I meant that the smem driver will 
>>> ever crash. The referred to crash in the cover letter is a crash in the 
>>> firmware running on the remoteproc. The remoteproc could crash for any 
>>> unexpected reason, related or unrelated to smem, while holding the tcsr 
>>> mutex. I want to ensure that all resources that a remoteproc might be 
>>> using are released as part of remoteproc stop.
>>>
>>> The SMEM driver manages the lock/unlock operations on the tcsr mutex 
>>> from the Linux CPU's perspective. This case is for cleaning up from the 
>>> remote side's perspective.
>>>
>>> In this case it's the hwspinlock used to synchronize SMEM, but it's 
>>> conceivable that firmware running on the remoteproc has additional locks 
>>> that need to be busted in order for the system to continue executing 
>>> until the firmware is reinitialized.
>>>
>>> We did consider tying this to the SMEM instance, but the entitiy 
>>> relating to firmware is the remoteproc instance.
>>
>> I still do not understand why you have to add hwlock to remoteproc, even
>> though it is not directly used. Your driver problem looks like lack of
>> proper driver architecture - you want to control the locks not from the
>> layer took the lock, but one layer up. Sorry, no, fix the driver
>> architecture.
>>
> 
> No, it is the firmware's reference to the lock that is represented in
> the remoteproc node, while SMEM deals with Linux's reference to the lock.
> 
> This reference would be used to release the lock - on behalf of the
> firmware - in the event that the firmware held it when it
> stopped/crashed.

I understood, but the remoteproc driver did not acquire the hardware
lock. It was taken by smem, if I got it correctly, so you should poke
smem to bust the spinlock.

The hwlock is not a property of remote proc, because remote proc does
not care, right? Other device cares... and now for every smem user you
will add new binding property?

No, you are adding a binding based on your driver solution.

Best regards,
Krzysztof