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Date:   Wed, 13 Jul 2022 17:57:35 -0700
From:   Guru Das Srinagesh <quic_gurus@quicinc.com>
To:     Rajendra Nayak <quic_rjendra@quicinc.com>
CC:     Andy Gross <agross@kernel.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        <linux-arm-msm@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        "David Heidelberg" <david@ixit.cz>,
        Robert Marko <robimarko@gmail.com>,
        Elliot Berman <quic_eberman@quicinc.com>
Subject: Re: [PATCH 5/5] firmware: qcom: scm: Add wait-queue handling logic
Message-ID: <20220714005735.GA22183@quicinc.com>
References: <1656359076-13018-1-git-send-email-quic_gurus@quicinc.com>
 <1656359076-13018-6-git-send-email-quic_gurus@quicinc.com>
 <ec04538b-93e2-fa93-4043-c489a0f228e8@quicinc.com>
 <ad5e875d-e5d7-3b6f-4915-98ba08df8c5d@quicinc.com>
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On Jul 01 2022 16:51, Rajendra Nayak wrote:
> 
> 
> On 7/1/2022 4:32 PM, Rajendra Nayak wrote:
> >
> >
> >On 6/28/2022 1:14 AM, Guru Das Srinagesh wrote:
> >>Add logic to handle QCOM_SCM_WAITQ_SLEEP or QCOM_SCM_WAITQ_WAKE return
> >>codes.
> >>
> >>Scenario 1: Requests made by 2 different VMs:
> >>
> >>   VM_1                     VM_2                            Firmware
> >>     │                        │                                 │
> >>     │                        │                                 │
> >>     │                        │                                 │
> >>     │                        │                                 │
> >>     │      REQUEST_1         │                                 │
> >>     ├────────────────────────┼─────────────────────────────────┤
> >>     │                        │                                 │
> >>     │                        │                              ┌──┼──┐
> >>     │                        │                              │  │  │
> >>     │                        │     REQUEST_2                │  │  │
> >>     │                        ├──────────────────────────────┼──┤  │
> >>     │                        │                              │  │  │Resource
> >>     │                        │                              │  │  │is busy
> >>     │                        │       {WQ_SLEEP}             │  │  │
> >>     │                        │◄─────────────────────────────┼──┤  │
> >>     │                        │  wq_ctx, smc_call_ctx        │  │  │
> >>     │                        │                              └──┼──┘
> >>     │   REQUEST_1 COMPLETE   │                                 │
> >>     │◄───────────────────────┼─────────────────────────────────┤
> >>     │                        │                                 │
> >>     │                        │         IRQ                     │
> >>     │                        │◄─-------------------------------│
> >>     │                        │                                 │
> >>     │                        │      get_wq_ctx()               │
> >>     │                        ├────────────────────────────────►│
> >>     │                        │                                 │
> >>     │                        │                                 │
> >>     │                        │◄────────────────────────────────┤
> >>     │                        │   wq_ctx, flags, and            │
> >>     │                        │        more_pending             │
> >>     │                        │                                 │
> >>     │                        │                                 │
> >>     │                        │ wq_resume(smc_call_ctx)         │
> >>     │                        ├────────────────────────────────►│
> >>     │                        │                                 │
> >>     │                        │                                 │
> >>     │                        │      REQUEST_2 COMPLETE         │
> >>     │                        │◄────────────────────────────────┤
> >>     │                        │                                 │
> >>     │                        │                                 │
> >>
> >>Scenario 2: Two Requests coming in from same VM:
> >>
> >>   VM_1                                                     Firmware
> >>     │                                                          │
> >>     │                                                          │
> >>     │                                                          │
> >>     │                                                          │
> >>     │      REQUEST_1                                           │
> >>     ├──────────────────────────────────────────────────────────┤
> >>     │                                                          │
> >>     │                                                     ┌────┼───┐
> >>     │                                                     │    │   │
> >>     │                                                     │    │   │
> >>     │                                                     │    │   │
> >>     │      REQUEST_2                                      │    │   │
> >>     ├─────────────────────────────────────────────────────┼───►│   │
> >>     │                                                     │    │   │Resource
> >>     │                                                     │    │   │is busy
> >>     │      {WQ_SLEEP}                                     │    │   │
> >>     │◄────────────────────────────────────────────────────┼────┤   │
> >>     │      wq_ctx, req2_smc_call_ctx                      │    │   │
> >>     │                                                     │    │   │
> >>     │                                                     └────┼───┘
> >>     │                                                          │
> >>     │      {WQ_WAKE}                                           │
> >>     │◄─────────────────────────────────────────────────────────┤
> >>     │      wq_ctx, req1_smc_call_ctx, flags                    │
> >
> >
> >This is perhaps the same thing I asked on the previous patch,
> >I am guessing {WQ_WAKE} is returned in respone to REQUEST_1?
> >How do you know in this case if REQUEST_1 was a success or failure?
> >
> 
> Ok looking at this some more, I think what we are saying is that the FW returns
> {WQ_WAKE} to REQUEST_1, we then call wq_wake_ack and the return of
> *that* will tell if REQUEST_1 was success or failure?
> Did I get it right?

Yes, that is correct. I should have added an explanatory note in the commit
message to this effect:


     │      {WQ_WAKE}                         <-- Return value  │
     │◄─────────────────────────────────────────────────────────┤
     │      wq_ctx, req1_smc_call_ctx, flags  <-- Its payload   │

What this means is that the WQ_WAKE is sent by the FW to VM1 (direction of
arrow is from right to left) and that the additional data packed as payload
indicate that it is meant for REQUEST_1 (`req1_smc_call_ctx`).

Hopefully this will help understand the diagram better.

Thank you.

Guru Das.