Re: [PATCH v2 07/14] remoteproc: Introduce function __rproc_detach()

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

On Fri, Nov 06, 2020 at 06:43:05PM +0100, Arnaud POULIQUEN wrote:
> 
> 
> On 10/30/20 8:57 PM, Mathieu Poirier wrote:
> > Introduce function __rproc_detach() to perform the same kind of
> > operation as rproc_stop(), but instead of switching off the
> > remote processor using rproc->ops->stop(), it uses
> > rproc->ops->detach().  That way it is possible for the core
> > to release the resources associated with a remote processor while
> > the latter is kept operating.
> > 
> > Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
> > Reviewed-by: Peng Fan <peng.fan@nxp.com>
> > ---
> >  drivers/remoteproc/remoteproc_core.c | 31 ++++++++++++++++++++++++++++
> >  1 file changed, 31 insertions(+)
> > 
> > diff --git a/drivers/remoteproc/remoteproc_core.c b/drivers/remoteproc/remoteproc_core.c
> > index ed1f9ca4248b..62e88ff65009 100644
> > --- a/drivers/remoteproc/remoteproc_core.c
> > +++ b/drivers/remoteproc/remoteproc_core.c
> > @@ -1664,6 +1664,37 @@ static int rproc_stop(struct rproc *rproc, bool crashed)
> >  	return 0;
> >  }
> >  
> > +/*
> > + * __rproc_detach(): Does the opposite of rproc_attach()
> > + */
> > +static int __maybe_unused __rproc_detach(struct rproc *rproc)
> > +{
> > +	struct device *dev = &rproc->dev;
> > +	int ret;
> > +
> > +	/* No need to continue if a detach() operation has not been provided */
> > +	if (!rproc->ops->detach)
> > +		return -EINVAL;
> > +
> > +	/* Stop any subdevices for the remote processor */
> > +	rproc_stop_subdevices(rproc, false);
> 
> How to determine whether a subdevice should be stopped or detached? 
> For instance, in ST, we have a resource manager subdev which maintains clocks and regulators
> for peripherals used by the remote processor.
> In case of detachment we would need to maintain clock and regulators.
> 
> > +
> > +	/* Tell the remote processor the core isn't available anymore */
> > +	ret = rproc->ops->detach(rproc);
> > +	if (ret) {
> > +		dev_err(dev, "can't detach from rproc: %d\n", ret);
> > +		rproc_start_subdevices(rproc);
> > +		return ret;
> > +	}
> > +
> > +	rproc_unprepare_subdevices(rproc);
> 
> Same here, is prepare/unprepare can depend on the operation?
> 
> Seems that adding rproc_attach_subdevices/rproc_detach_subdevices could be not sufficient
> to address prepare/unprepare.
> Alternative could be:
> - extra parameter for the subdev ops to indicate attach/detach action...?
> - intermediate rproc state : ATTACHING, DETACHING
> - other?

These are really good points.  I did not think about that kind of scenario and
the best solution isn't obvious to me either.

> 
> That's said, I don't think that it is blocking for the ST resource manager.
> In this particular case, regulators and clocks can be permanently activated
> as a back-up solution (always-on).
> 
> So, if no other company has a problem with that, we can keep this implementation for now.

As I wrote above the path forward isn't clear to me and as such will opt to
address this in another patchset...  But it has to be fixed. 

> 
> Regards,
> Arnaud
> 
> > +
> > +	rproc->state = RPROC_DETACHED;
> > +
> > +	dev_info(dev, "detached remote processor %s\n", rproc->name);
> > +
> > +	return 0;
> > +}
> >  
> >  /**
> >   * rproc_trigger_recovery() - recover a remoteproc
> >