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Subject: Re: [PATCH v3 12/14] remoteproc: Introducing function
 rproc_set_state_machine()
To:     Mathieu Poirier <mathieu.poirier@linaro.org>
CC:     <bjorn.andersson@linaro.org>, <ohad@wizery.com>,
        <loic.pallardy@st.com>, <s-anna@ti.com>,
        <linux-remoteproc@vger.kernel.org>, <corbet@lwn.net>,
        <linux-doc@vger.kernel.org>, <linux-kernel@vger.kernel.org>
References: <20200424200135.28825-1-mathieu.poirier@linaro.org>
 <20200424200135.28825-13-mathieu.poirier@linaro.org>
 <d297aeab-4f7e-95e0-04c0-266e0f08b2d0@st.com> <20200430204233.GB18004@xps15>
From:   Arnaud POULIQUEN <arnaud.pouliquen@st.com>
Message-ID: <842d64d8-832a-cc4c-cbe1-dbd4654fcdd5@st.com>
Date:   Mon, 4 May 2020 13:57:59 +0200
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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@linaro.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"?

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);
>>>