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Date:   Tue, 5 May 2020 16:03:27 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Arnaud POULIQUEN <arnaud.pouliquen@...com>
Cc:     bjorn.andersson@...aro.org, ohad@...ery.com, loic.pallardy@...com,
        s-anna@...com, linux-remoteproc@...r.kernel.org, corbet@....net,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 10/14] remoteproc: Deal with synchronisation when
 shutting down

On Mon, May 04, 2020 at 01:34:43PM +0200, Arnaud POULIQUEN wrote:
> 
> 
> On 4/30/20 10:23 PM, Mathieu Poirier wrote:
> > On Wed, Apr 29, 2020 at 10:19:49AM +0200, Arnaud POULIQUEN wrote:
> >>
> >>
> >> On 4/24/20 10:01 PM, Mathieu Poirier wrote:
> >>> The remoteproc core must not allow function rproc_shutdown() to
> >>> proceed if currently synchronising with a remote processor and
> >>> the synchronisation operations of that remote processor does not
> >>> support it.  Also part of the process is to set the synchronisation
> >>> flag so that the remoteproc core can make the right decisions when
> >>> restarting the system.
> >>>
> >>> Signed-off-by: Mathieu Poirier <mathieu.poirier@...aro.org>
> >>> ---
> >>>  drivers/remoteproc/remoteproc_core.c     | 32 ++++++++++++++++++++++++
> >>>  drivers/remoteproc/remoteproc_internal.h |  7 ++++++
> >>>  2 files changed, 39 insertions(+)
> >>>
> >>> diff --git a/drivers/remoteproc/remoteproc_core.c b/drivers/remoteproc/remoteproc_core.c
> >>> index 3a84a38ba37b..48afa1f80a8f 100644
> >>> --- a/drivers/remoteproc/remoteproc_core.c
> >>> +++ b/drivers/remoteproc/remoteproc_core.c
> >>> @@ -1849,6 +1849,27 @@ int rproc_boot(struct rproc *rproc)
> >>>  }
> >>>  EXPORT_SYMBOL(rproc_boot);
> >>>  
> >>> +static bool rproc_can_shutdown(struct rproc *rproc)
> >>> +{
> >>> +	/*
> >>> +	 * The remoteproc core is the lifecycle manager, no problem
> >>> +	 * calling for a shutdown.
> >>> +	 */
> >>> +	if (!rproc_needs_syncing(rproc))
> >>> +		return true;
> >>> +
> >>> +	/*
> >>> +	 * The remoteproc has been loaded by another entity (as per above
> >>> +	 * condition) and the platform code has given us the capability
> >>> +	 * of stopping it.
> >>> +	 */
> >>> +	if (rproc->sync_ops->stop)
> >>> +		return true;
> >>
> >> This means that if rproc->sync_ops->stop is null rproc_stop_subdevices will not
> >> be called? seems not symmetric with the start sequence.
> > 
> > If rproc->sync_ops->stop is not provided then the remoteproc core can't stop the
> > remote processor at all after it has synchronised with it.  If a usecase
> > requires some kind of soft reset then a stop() function that uses a mailbox
> > notification or some other mechanism can be provided to tell the remote
> > processor to put itself back in startup mode again.
> > 
> > Is this fine with you or there is still something I don't get?
> 
> My point here is more around the subdevices. But perhaps i missed something...
> 
> In rproc_start rproc_start_subdevices is called, even if sync_start is null.

Here I'll take that you mean sync_ops::start()

> But in rproc_shutdown rproc_stop is not called, if sync_ops->stop is null.
> So rproc_stop_subdevices is not called in this case.

Correct.  I am pretty sure some people don't want the remoteproc core to be able
to do anything other than synchronise with a remote processor, be it at boot
time or when the remote processor has crashed.

I can also see scenarios where people want to be able to start and stop
subdevices from the remoteproc core, but _not_ power cycle the remote processor.
In such cases the sync_ops::stop() should be some kind of notification telling
the remote processor to put itself back in initialisation mode and
sync_flags.after_stop should be set to true.

> Then if sync_flags.after_stop is false, it looks like that something will go wrong
> at next start.

If sync_ops::stop is NULL then the value of sync_flags.after_stop becomes
irrelevant because that state can't be reached. Let me know if you found a
condition where this isn't the case and I will correct it. 

> 
> > 
> >> Probably not useful to test it here as condition is already handled in rproc_stop_device...
> >>
> >> Regards
> >> Arnaud
> >>> +
> >>> +	/* Any other condition should not be allowed */
> >>> +	return false;
> >>> +}
> >>> +
> >>>  /**
> >>>   * rproc_shutdown() - power off the remote processor
> >>>   * @rproc: the remote processor
> >>> @@ -1879,6 +1900,9 @@ void rproc_shutdown(struct rproc *rproc)
> >>>  		return;
> >>>  	}
> >>>  
> >>> +	if (!rproc_can_shutdown(rproc))
> >>> +		goto out;
> >>> +
> >>>  	/* if the remote proc is still needed, bail out */
> >>>  	if (!atomic_dec_and_test(&rproc->power))
> >>>  		goto out;
> >>> @@ -1898,6 +1922,14 @@ void rproc_shutdown(struct rproc *rproc)
> >>>  	kfree(rproc->cached_table);
> >>>  	rproc->cached_table = NULL;
> >>>  	rproc->table_ptr = NULL;
> >>> +
> >>> +	/*
> >>> +	 * The remote processor has been switched off - tell the core what
> >>> +	 * operation to use from hereon, i.e whether an external entity will
> >>> +	 * reboot the remote processor or it is now the remoteproc core's
> >>> +	 * responsability.
> >>> +	 */
> >>> +	rproc_set_sync_flag(rproc, RPROC_SYNC_STATE_SHUTDOWN);
> >>>  out:
> >>>  	mutex_unlock(&rproc->lock);
> >>>  }
> >>> diff --git a/drivers/remoteproc/remoteproc_internal.h b/drivers/remoteproc/remoteproc_internal.h
> >>> index 61500981155c..7dcc0a26892b 100644
> >>> --- a/drivers/remoteproc/remoteproc_internal.h
> >>> +++ b/drivers/remoteproc/remoteproc_internal.h
> >>> @@ -27,6 +27,9 @@ struct rproc_debug_trace {
> >>>  /*
> >>>   * enum rproc_sync_states - remote processsor sync states
> >>>   *
> >>> + * @RPROC_SYNC_STATE_SHUTDOWN	state to use after the remoteproc core
> >>> + *				has shutdown (rproc_shutdown()) the
> >>> + *				remote processor.
> >>>   * @RPROC_SYNC_STATE_CRASHED	state to use after the remote processor
> >>>   *				has crashed but has not been recovered by
> >>>   *				the remoteproc core yet.
> >>> @@ -36,6 +39,7 @@ struct rproc_debug_trace {
> >>>   * operation to use.
> >>>   */
> >>>  enum rproc_sync_states {
> >>> +	RPROC_SYNC_STATE_SHUTDOWN,
> >>>  	RPROC_SYNC_STATE_CRASHED,
> >>>  };
> >>>  
> >>> @@ -43,6 +47,9 @@ static inline void rproc_set_sync_flag(struct rproc *rproc,
> >>>  				       enum rproc_sync_states state)
> >>>  {
> >>>  	switch (state) {
> >>> +	case RPROC_SYNC_STATE_SHUTDOWN:
> >>> +		rproc->sync_with_rproc = rproc->sync_flags.after_stop;
> >>> +		break;
> >>>  	case RPROC_SYNC_STATE_CRASHED:
> >>>  		rproc->sync_with_rproc = rproc->sync_flags.after_crash;
> >>>  		break;
> >>>

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