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Date:   Tue, 5 May 2020 15:43:18 -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 12/14] remoteproc: Introducing function
 rproc_set_state_machine()

On Mon, May 04, 2020 at 01:57:59PM +0200, Arnaud POULIQUEN wrote:
> 
> 
> On 4/30/20 10:42 PM, Mathieu Poirier wrote:
> > On Wed, Apr 29, 2020 at 11:22:28AM +0200, Arnaud POULIQUEN wrote:
> >>
> >>
> >> On 4/24/20 10:01 PM, Mathieu Poirier wrote:
> >>> Introducting function rproc_set_state_machine() to add
> >>> operations and a set of flags to use when synchronising with
> >>> a remote processor.
> >>>
> >>> Signed-off-by: Mathieu Poirier <mathieu.poirier@...aro.org>
> >>> ---
> >>>  drivers/remoteproc/remoteproc_core.c     | 54 ++++++++++++++++++++++++
> >>>  drivers/remoteproc/remoteproc_internal.h |  6 +++
> >>>  include/linux/remoteproc.h               |  3 ++
> >>>  3 files changed, 63 insertions(+)
> >>>
> >>> diff --git a/drivers/remoteproc/remoteproc_core.c b/drivers/remoteproc/remoteproc_core.c
> >>> index 48afa1f80a8f..5c48714e8702 100644
> >>> --- a/drivers/remoteproc/remoteproc_core.c
> >>> +++ b/drivers/remoteproc/remoteproc_core.c
> >>> @@ -2065,6 +2065,59 @@ int devm_rproc_add(struct device *dev, struct rproc *rproc)
> >>>  }
> >>>  EXPORT_SYMBOL(devm_rproc_add);
> >>>  
> >>> +/**
> >>> + * rproc_set_state_machine() - Set a synchronisation ops and set of flags
> >>> + *			       to use with a remote processor
> >>> + * @rproc:	The remote processor to work with
> >>> + * @sync_ops:	The operations to use when synchronising with a remote
> >>> + *		processor
> >>> + * @sync_flags:	The flags to use when deciding if the remoteproc core
> >>> + *		should be synchronising with a remote processor
> >>> + *
> >>> + * Returns 0 on success, an error code otherwise.
> >>> + */
> >>> +int rproc_set_state_machine(struct rproc *rproc,
> >>> +			    const struct rproc_ops *sync_ops,
> >>> +			    struct rproc_sync_flags sync_flags)
> >>
> >> So this API should be called by platform driver only in case of synchronization
> >> support, right?
> > 
> > Correct
> > 
> >> In this case i would rename it as there is also a state machine in "normal" boot
> >> proposal: rproc_set_sync_machine or rproc_set_sync_state_machine
> > 
> > That is a valid observation - rproc_set_sync_state_machine() sounds descriptive
> > enough for me.
> > 
> >>
> >>> +{
> >>> +	if (!rproc || !sync_ops)
> >>> +		return -EINVAL;
> >>> +
> >>> +	/*
> >>> +	 * No point in going further if we never have to synchronise with
> >>> +	 * the remote processor.
> >>> +	 */
> >>> +	if (!sync_flags.on_init &&
> >>> +	    !sync_flags.after_stop && !sync_flags.after_crash)
> >>> +		return 0;
> >>> +
> >>> +	/*
> >>> +	 * Refuse to go further if remoteproc operations have been allocated
> >>> +	 * but they will never be used.
> >>> +	 */
> >>> +	if (rproc->ops && sync_flags.on_init &&
> >>> +	    sync_flags.after_stop && sync_flags.after_crash)
> >>> +		return -EINVAL;
> >>> +
> >>> +	/*
> >>> +	 * Don't allow users to set this more than once to avoid situations
> >>> +	 * where the remote processor can't be recovered.
> >>> +	 */
> >>> +	if (rproc->sync_ops)
> >>> +		return -EINVAL;
> >>> +
> >>> +	rproc->sync_ops = kmemdup(sync_ops, sizeof(*sync_ops), GFP_KERNEL);
> >>> +	if (!rproc->sync_ops)
> >>> +		return -ENOMEM;
> >>> +
> >>> +	rproc->sync_flags = sync_flags;
> >>> +	/* Tell the core what to do when initialising */
> >>> +	rproc_set_sync_flag(rproc, RPROC_SYNC_STATE_INIT);
> >>
> >> Is there a use case where sync_flags.on_init is false and other flags are true?
> > 
> > I haven't seen one yet, which doesn't mean it doesn't exist or won't in the
> > future.  I wanted to make this as flexible as possible.  I started with the idea
> > of making synchronisation at initialisation time implicit if
> > rproc_set_state_machine() is called but I know it is only a matter of time
> > before people come up with some exotic use case where .on_init is false.
> 
> So having on_init false but after_crash && after_stop true, means loading the
> firmware on first start, and the synchronize with it, right?
> Yes probably could be an exotic valid use case. :) 
> 
> > 
> >>
> >> Look like on_init is useless and should not be exposed to the platform driver.
> >> Or comments are missing to explain the usage of it vs the other flags.
> > 
> > Comments added in remoteproc_internal.h and the new section in
> > Documentation/remoteproc.txt aren't sufficient?  Can you give me a hint as to
> > what you think is missing?
> 
> IMO something is quite confusing...
> On one side on_init can be set to false.
> But on the other side the flag is set  by call rproc_set_state_machine.
> In Documentation/remoteproc.txt rproc_set_state_machine description is:
> 
> "This function should be called for cases where the remote processor has
> been started by another entity, be it a boot loader or trusted environment,
> and the remoteproc core is to synchronise with the remote processor rather
> then boot it."
> 
> So how on_init could be false if "the remote processor has
> been started by another entity"?

I see your point and I think it is a question of documentation.  I will rephrase
this to be more accurate.

> 
> Regards,
> Arnaud
> 
> > 
> >>
> >> Regards,
> >> Arnaud
> >>  
> >>> +
> >>> +	return 0;
> >>> +}
> >>> +EXPORT_SYMBOL(rproc_set_state_machine);
> >>> +
> >>>  /**
> >>>   * rproc_type_release() - release a remote processor instance
> >>>   * @dev: the rproc's device
> >>> @@ -2088,6 +2141,7 @@ static void rproc_type_release(struct device *dev)
> >>>  	kfree_const(rproc->firmware);
> >>>  	kfree_const(rproc->name);
> >>>  	kfree(rproc->ops);
> >>> +	kfree(rproc->sync_ops);
> >>>  	kfree(rproc);
> >>>  }
> >>>  
> >>> diff --git a/drivers/remoteproc/remoteproc_internal.h b/drivers/remoteproc/remoteproc_internal.h
> >>> index 7dcc0a26892b..c1a293a37c78 100644
> >>> --- a/drivers/remoteproc/remoteproc_internal.h
> >>> +++ b/drivers/remoteproc/remoteproc_internal.h
> >>> @@ -27,6 +27,8 @@ struct rproc_debug_trace {
> >>>  /*
> >>>   * enum rproc_sync_states - remote processsor sync states
> >>>   *
> >>> + * @RPROC_SYNC_STATE_INIT	state to use when the remoteproc core
> >>> + *				is initialising.
> >>>   * @RPROC_SYNC_STATE_SHUTDOWN	state to use after the remoteproc core
> >>>   *				has shutdown (rproc_shutdown()) the
> >>>   *				remote processor.
> >>> @@ -39,6 +41,7 @@ struct rproc_debug_trace {
> >>>   * operation to use.
> >>>   */
> >>>  enum rproc_sync_states {
> >>> +	RPROC_SYNC_STATE_INIT,
> >>>  	RPROC_SYNC_STATE_SHUTDOWN,
> >>>  	RPROC_SYNC_STATE_CRASHED,
> >>>  };
> >>> @@ -47,6 +50,9 @@ static inline void rproc_set_sync_flag(struct rproc *rproc,
> >>>  				       enum rproc_sync_states state)
> >>>  {
> >>>  	switch (state) {
> >>> +	case RPROC_SYNC_STATE_INIT:
> >>> +		rproc->sync_with_rproc = rproc->sync_flags.on_init;
> >>> +		break;
> >>>  	case RPROC_SYNC_STATE_SHUTDOWN:
> >>>  		rproc->sync_with_rproc = rproc->sync_flags.after_stop;
> >>>  		break;
> >>> diff --git a/include/linux/remoteproc.h b/include/linux/remoteproc.h
> >>> index ceb3b2bba824..a75ed92b3de6 100644
> >>> --- a/include/linux/remoteproc.h
> >>> +++ b/include/linux/remoteproc.h
> >>> @@ -619,6 +619,9 @@ struct rproc *rproc_get_by_child(struct device *dev);
> >>>  struct rproc *rproc_alloc(struct device *dev, const char *name,
> >>>  			  const struct rproc_ops *ops,
> >>>  			  const char *firmware, int len);
> >>> +int rproc_set_state_machine(struct rproc *rproc,
> >>> +			    const struct rproc_ops *sync_ops,
> >>> +			    struct rproc_sync_flags sync_flags);
> >>>  void rproc_put(struct rproc *rproc);
> >>>  int rproc_add(struct rproc *rproc);
> >>>  int rproc_del(struct rproc *rproc);
> >>>

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