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

[Mathieu Poirier <mathieu.poirier@linaro.org>]

Hi Suman,

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.
> 
> >> 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.

I didn't notice this comment upon first read... Can you give me more details on
what your usecase is order to see how best to deal with it?

Thanks,
Mathieu

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