Re: [PATCH v2 16/17] remoteproc: Correctly deal with MCU synchronisation when changing state

[Suman Anna <s-anna@ti.com>]

On 4/1/20 4:29 PM, Mathieu Poirier wrote:
> On Tue, Mar 31, 2020 at 05:35:58PM -0500, Suman Anna wrote:
>> Hi Mathieu,
>>
>> On 3/30/20 6:49 PM, Mathieu Poirier wrote:
>>> On Fri, Mar 27, 2020 at 02:04:36PM +0000, Loic PALLARDY wrote:
>>>>
>>>>
>>>>> -----Original Message-----
>>>>> From: Mathieu Poirier <mathieu.poirier@linaro.org>
>>>>> Sent: mardi 24 mars 2020 22:46
>>>>> To: bjorn.andersson@linaro.org
>>>>> Cc: ohad@wizery.com; Loic PALLARDY <loic.pallardy@st.com>; s-
>>>>> anna@ti.com; peng.fan@nxp.com; Arnaud POULIQUEN
>>>>> <arnaud.pouliquen@st.com>; Fabien DESSENNE
>>>>> <fabien.dessenne@st.com>; linux-remoteproc@vger.kernel.org
>>>>> Subject: [PATCH v2 16/17] remoteproc: Correctly deal with MCU
>>>>> synchronisation when changing state
>>>>>
>>>>> This patch deals with state changes when synchronising with an MCU. More
>>>>> specifically it prevents the MCU from being started if it already has been
>>>>> started by another entity.  Similarly it prevents the AP from stopping the
>>>>> MCU if it hasn't been given the capability by platform firmware.
>>>>>
>>>>> Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
>>>>> ---
>>>>>  drivers/remoteproc/remoteproc_sysfs.c | 32
>>>>> ++++++++++++++++++++++++++-
>>>>>  1 file changed, 31 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/remoteproc/remoteproc_sysfs.c
>>>>> b/drivers/remoteproc/remoteproc_sysfs.c
>>>>> index 4956577ad4b4..741a3c152b82 100644
>>>>> --- a/drivers/remoteproc/remoteproc_sysfs.c
>>>>> +++ b/drivers/remoteproc/remoteproc_sysfs.c
>>>>> @@ -108,6 +108,29 @@ static ssize_t state_show(struct device *dev, struct
>>>>> device_attribute *attr,
>>>>>  	return sprintf(buf, "%s\n", rproc_state_string[state]);
>>>>>  }
>>>>>
>>>>> +static int rproc_can_shutdown(struct rproc *rproc)
>>>>> +{
>>>>> +	/* The MCU is not running, obviously an invalid operation. */
>>>>> +	if (rproc->state != RPROC_RUNNING)
>>>>> +		return false;
>>>>> +
>>>>> +	/*
>>>>> +	 * The MCU is not running (see above) and the remoteproc core is
>>>>> the
>>>>> +	 * lifecycle manager, no problem calling for a shutdown.
>>>>> +	 */
>>>>> +	if (!rproc_sync_with_mcu(rproc))
>>>>> +		return true;
>>>>> +
>>>>> +	/*
>>>>> +	 * The MCU has been loaded by another entity (see above) and the
>>>>> +	 * platform code has _not_ given us the capability of stopping it.
>>>>> +	 */
>>>>> +	if (!rproc->sync_ops->stop)
>>>>> +		return false;
>>>>
>>>> Test could be simplified
>>>> if (rproc_sync_with_mcu(rproc)) && !rproc->sync_ops->stop)
>>>> 	return false;
>>>
>>> I laid out the test individually on purpose.  That way there is no coupling
>>> between conditions, it is plane to see what is going on and remains maintainable
>>> as we add new tests.
>>>
>>>>
>>>>> +
>>>>> +	return true;
>>>>> +}
>>>>> +
>>>>>  /* Change remote processor state via sysfs */
>>>>>  static ssize_t state_store(struct device *dev,
>>>>>  			      struct device_attribute *attr,
>>>>> @@ -120,11 +143,18 @@ static ssize_t state_store(struct device *dev,
>>>>>  		if (rproc->state == RPROC_RUNNING)
>>>>>  			return -EBUSY;
>>>>>
>>>>> +		/*
>>>>> +		 * In synchronisation mode, booting the MCU is the
>>>>> +		 * responsibility of an external entity.
>>>>> +		 */
>>>>> +		if (rproc_sync_with_mcu(rproc))
>>>>> +			return -EINVAL;
>>>>> +
>>>> I don't understand this restriction, simply because it is preventing to resynchronize with a
>>>> coprocessor after a "stop".
>>
>> There's actually one more scenario even without "stop". If auto_boot is
>> set to false, then rproc_actuate will never get called.
> 
> I fail to fully understand the situation you are describing - can you give me
> more information?

The platform driver has auto_boot set to false and sync_states set, so
rproc_trigger_auto_initiate() never gets called in rproc_add(), and
rproc_actuate() doesn't happen either. rproc->state is not RUNNING, and
you will bail out here, and there is no way to start it either.

> 
>>
>>>> In the following configuration which can be configuration for coprocessor with romed/flashed
>>>> firmware (no reload needed):
>>>> on_init = true
>>>> after_stop = true
>>>> after_crash = true
>>>> Once you stop it via sysfs interface, you can't anymore restart/resync to it.
>>>
>>> Very true.  The MCU will get restarted by another entity but the AP won't
>>> synchronise with it.  I need more time to think about the best way to deal with
>>> this and may have to get back to you for further discussions.
>>>
>>>>
>>>> I think it will be better to modify rproc_boot() to take into account rproc_sync_with_mcu()
>>>> as below:
>>>>
>>>> int rproc_boot(struct rproc *rproc)
>>>>  {
>>>> -	const struct firmware *firmware_p;
>>>> +	const struct firmware *firmware_p = NULL;
>>>>  	struct device *dev = &rproc->dev;
>>>>  	int ret;
>>>>  
>>>>  	if (!rproc) {
>>>>  		pr_err("invalid rproc handle\n");
>>>>  		return -EINVAL;
>>>>  	}
>>>>  
>>>>  	/* load firmware */
>>>> -	ret = request_firmware(&firmware_p, rproc->firmware, dev);
>>>> -	if (ret < 0) {
>>>> -		dev_err(dev, "request_firmware failed: %d\n", ret);
>>>> -		return ret;
>>>> +	if (!rproc_sync_with_mcu(rproc)) {
>>
>> I guess this is what the original skip_fw_load was doing. And with the
>> current series, the userspace loading support usecase I have cannot be
>> achieved. If this is added back, I can try if that works for my usecases.
>>
>>>> +		ret = request_firmware(&firmware_p, rproc->firmware, dev);
>>>> +		if (ret < 0) {
>>>> +			dev_err(dev, "request_firmware failed: %d\n", ret);
>>>> +			return ret;
>>>> +		}
>>>>  	}
>>>>  
>>>>  	ret = rproc_actuate(rproc, firmware_p);
>>>>  
>>>> -	release_firmware(firmware_p);
>>>> +	if (firmware_p)
>>>> +		release_firmware(firmware_p);
>>>>  
>>>>  	return ret;
>>>>  }
>>>>  
>>>> Thanks to these modifications, I'm able to resync after a stop with coprocessor without reloading firmware.
>>>>
>>>>>  		ret = rproc_boot(rproc);
>>>>>  		if (ret)
>>>>>  			dev_err(&rproc->dev, "Boot failed: %d\n", ret);
>>>>>  	} else if (sysfs_streq(buf, "stop")) {
>>>>> -		if (rproc->state != RPROC_RUNNING)
>>>>> +		if (!rproc_can_shutdown(rproc))
>>>>>  			return -EINVAL;
>>>>>
>>>>>  		rproc_shutdown(rproc);
>>>> As rproc shutdown is also accessible as kernel API, I propose to move
>>>> rproc_can_shutdown() check inside rproc_shutdown() and to test
>>>> returned error
>>>
>>> Ah yes, it is public...  As you point out, I think we'll need to move
>>> rproc_can_shutdown() in rproc_shutdown().
>>
>> I am assuming only the new conditions, right?
> 
> Once again I fail to grasp the extent of your comment.  Can you be more specific
> about the "new conditions"?

rproc_can_shutdown() has three checks, where the first check is existing
check that got moved, and the other 2 are the new checks that deal with
the sync states. So, I meant these 2 new sync checks.

regards
Suman

> 
> Thanks
> Mathieu
> 
>>
>> regards
>> Suman
>>
>>>
>>> Thank you for taking the time to review this set,
>>> Mathieu
>>>