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Date:   Wed, 29 Jan 2020 13:15:46 -0700
From:   Mathieu Poirier <mathieu.poirier@linaro.org>
To:     Arnaud POULIQUEN <arnaud.pouliquen@st.com>
Cc:     Bjorn Andersson <bjorn.andersson@linaro.org>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Ohad Ben-Cohen <ohad@wizery.com>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        devicetree@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-remoteproc <linux-remoteproc@vger.kernel.org>,
        Sibi Sankar <sibis@codeaurora.org>,
        Rishabh Bhatnagar <rishabhb@codeaurora.org>
Subject: Re: [PATCH v2 7/8] remoteproc: qcom: q6v5: Add common panic handler
Message-ID: <20200129201546.GA31696@xps15>
References: <20191227053215.423811-1-bjorn.andersson@linaro.org>
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On Mon, Jan 27, 2020 at 10:46:05AM +0100, Arnaud POULIQUEN wrote:
> 
> 
> On 1/24/20 7:44 PM, Mathieu Poirier wrote:
> > On Thu, 23 Jan 2020 at 10:49, Arnaud POULIQUEN <arnaud.pouliquen@st.com> wrote:
> >>
> >> Hi Bjorn, Mathieu
> >>
> >> On 1/23/20 6:15 PM, Bjorn Andersson wrote:
> >>> On Thu 23 Jan 09:01 PST 2020, Mathieu Poirier wrote:
> >>>
> >>>> On Wed, 22 Jan 2020 at 12:40, Bjorn Andersson
> >>>> <bjorn.andersson@linaro.org> wrote:
> >>>>>
> >>>>> On Fri 10 Jan 13:28 PST 2020, Mathieu Poirier wrote:
> >>>>>
> >>>>>> On Thu, Dec 26, 2019 at 09:32:14PM -0800, Bjorn Andersson wrote:
> >>>>>>> Add a common panic handler that invokes a stop request and sleep enough
> >>>>>>> to let the remoteproc flush it's caches etc in order to aid post mortem
> >>>>>>> debugging.
> >>>>>>>
> >>>>>>> Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
> >>>>>>> ---
> >>>>>>>
> >>>>>>> Changes since v1:
> >>>>>>> - None
> >>>>>>>
> >>>>>>>  drivers/remoteproc/qcom_q6v5.c | 19 +++++++++++++++++++
> >>>>>>>  drivers/remoteproc/qcom_q6v5.h |  1 +
> >>>>>>>  2 files changed, 20 insertions(+)
> >>>>>>>
> >>>>>>> diff --git a/drivers/remoteproc/qcom_q6v5.c b/drivers/remoteproc/qcom_q6v5.c
> >>>>>>> index cb0f4a0be032..17167c980e02 100644
> >>>>>>> --- a/drivers/remoteproc/qcom_q6v5.c
> >>>>>>> +++ b/drivers/remoteproc/qcom_q6v5.c
> >>>>>>> @@ -6,6 +6,7 @@
> >>>>>>>   * Copyright (C) 2014 Sony Mobile Communications AB
> >>>>>>>   * Copyright (c) 2012-2013, The Linux Foundation. All rights reserved.
> >>>>>>>   */
> >>>>>>> +#include <linux/delay.h>
> >>>>>>>  #include <linux/kernel.h>
> >>>>>>>  #include <linux/platform_device.h>
> >>>>>>>  #include <linux/interrupt.h>
> >>>>>>> @@ -15,6 +16,8 @@
> >>>>>>>  #include <linux/remoteproc.h>
> >>>>>>>  #include "qcom_q6v5.h"
> >>>>>>>
> >>>>>>> +#define Q6V5_PANIC_DELAY_MS        200
> >>>>>>> +
> >>>>>>>  /**
> >>>>>>>   * qcom_q6v5_prepare() - reinitialize the qcom_q6v5 context before start
> >>>>>>>   * @q6v5:  reference to qcom_q6v5 context to be reinitialized
> >>>>>>> @@ -162,6 +165,22 @@ int qcom_q6v5_request_stop(struct qcom_q6v5 *q6v5)
> >>>>>>>  }
> >>>>>>>  EXPORT_SYMBOL_GPL(qcom_q6v5_request_stop);
> >>>>>>>
> >>>>>>> +/**
> >>>>>>> + * qcom_q6v5_panic() - panic handler to invoke a stop on the remote
> >>>>>>> + * @q6v5:  reference to qcom_q6v5 context
> >>>>>>> + *
> >>>>>>> + * Set the stop bit and sleep in order to allow the remote processor to flush
> >>>>>>> + * its caches etc for post mortem debugging.
> >>>>>>> + */
> >>>>>>> +void qcom_q6v5_panic(struct qcom_q6v5 *q6v5)
> >>>>>>> +{
> >>>>>>> +   qcom_smem_state_update_bits(q6v5->state,
> >>>>>>> +                               BIT(q6v5->stop_bit), BIT(q6v5->stop_bit));
> >>>>>>> +
> >>>>>>> +   mdelay(Q6V5_PANIC_DELAY_MS);
> >>>>>>
> >>>>>> I really wonder if the delay should be part of the remoteproc core and
> >>>>>> configurable via device tree.  Wanting the remote processor to flush its caches
> >>>>>> is likely something other vendors will want when dealing with a kernel panic.
> >>>>>> It would be nice to see if other people have an opinion on this topic.  If not
> >>>>>> then we can keep the delay here and move it to the core if need be.
> >>>>>>
> >>>>>
> >>>>> I gave this some more thought and what we're trying to achieve is to
> >>>>> signal the remote processors about the panic and then give them time to
> >>>>> react, but per the proposal (and Qualcomm downstream iirc) we will do
> >>>>> this for each remote processor, one by one.
> >>>>>
> >>>>> So in the typical case of a Qualcomm platform with 4-5 remoteprocs we'll
> >>>>> end up giving the first one a whole second to react and the last one
> >>>>> "only" 200ms.
> >>>>>
> >>>>> Moving the delay to the core by iterating over rproc_list calling
> >>>>> panic() and then delaying would be cleaner imo.
> >>>>
> >>>> I agree.
> >>>>
> >>>>>
> >>>>> It might be nice to make this configurable in DT, but I agree that it
> >>>>> would be nice to hear from others if this would be useful.
> >>>>
> >>>> I think the delay has to be configurable via DT if we move this to the
> >>>> core.  The binding can be optional and default to 200ms if not
> >>>> present.
> >>>>
> >>>
> >>> How about I make the panic() return the required delay and then we let
> >>> the core sleep for MAX() of the returned durations?
> > 
> > I like it.
> > 
> >> That way the default
> >>> is still a property of the remoteproc drivers - and 200ms seems rather
> >>> arbitrary to put in the core, even as a default.
> >>
> >> I agree with Bjorn, the delay should be provided by the platform.
> >> But in this case i wonder if it is simpler to just let the platform take care it?
> > 
> > If I understand you correctly, that is what Bjorn's original
> > implementation was doing and it had drawbacks.
> Yes, 
> Please tell me if i missed something, the only drawback seems mentioned is the accumulative delay.

Yes, that is correct.

> Could you elaborate how to implement the delay in remote proc core for multi rproc instance.
> Here is my view:
> To optimize the delay it would probably be necessary to compute:
> - the delay based on an initial date,
> - the delay requested by each rproc instance,
> - the delay elapsed in each rproc panic ops.
> Feasible but not straight forward... 
> So I suppose that you are thinking about a solution based on the store of the max delay that would be applied after last panic() return?

Yes

> anyway, how do you determine the last rproc instance? seems that a prerequisite would be that the panic ops is mandatory... 

Each ->panic() should return the amount of time to way or 0 if no delay is
required.  If an rpoc doesn't implement ->panic() then it is treated as 0.
From there wait for the maximum time that was collected.

It would be possible to do something more complicated like taking timestamps
everytime a ->panic() returns and optimize the time to wait for but that may be
for a future set.  The first implementation could go with an simple heuristic as
detailed above.

> 
> I'm not familiar with panic mechanism, but how panic ops are scheduled in SMP? Does panics ops would be treated in parallel (using msleep instead of mdelay)?
> In this case delays could not be cumulative...

The processor that triggered the panic sequentially runs the notifier registered
with the panic_notifier_list.  Other processors are instructed to take
themselves offline.  As such there won't be multiple ->panic() running
concurrently. 

> 
> > 
> >> For instance for stm32mp1 the stop corresponds to the reset on the remote processor core. To inform the coprocessor about an imminent shutdown we use a signal relying on a mailbox (cf. stm32_rproc_stop).
> >> In this case we would need a delay between the signal and the reset, but not after (no cache management).
> > 
> > Here I believe you are referring to the upper limit of 500ms that is
> > needed for the mbox_send_message() in stm32_rproc_stop() to complete.
> > Since that is a blocking call I think it would fit with Bjorn's
> > proposal above if a value of '0' is returned by rproc->ops->panic().
> > That would mean no further delays are needed (because the blocking
> > mbox_send_message() would have done the job already).  Let me know if
> > I'm in the weeds.
> Yes you are :), this is what i thought, if delay implemented in core.

Not sure I understand your last reply but I _think_ we are saying the same
thing.

> 
> Regards,
> Arnaud
> 
> > 
> >>
> >> Regards,
> >> Arnaud
> >>>
> >>> Regards,
> >>> Bjorn
> >>>