Re: [PATCH v2 08/14] remoteproc: Introduce function rproc_detach()

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

On Mon, Nov 09, 2020 at 10:05:35AM +0100, Arnaud POULIQUEN wrote:
> Hi Mathieu,
> 
> On 10/30/20 8:57 PM, Mathieu Poirier wrote:
> > Introduce function rproc_detach() to enable the remoteproc
> > core to release the resources associated with a remote processor
> > without stopping its operation.
> > 
> > Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
> > Reviewed-by: Peng Fan <peng.fan@nxp.com>
> > ---
> >  drivers/remoteproc/remoteproc_core.c | 65 +++++++++++++++++++++++++++-
> >  include/linux/remoteproc.h           |  1 +
> >  2 files changed, 65 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/remoteproc/remoteproc_core.c b/drivers/remoteproc/remoteproc_core.c
> > index 62e88ff65009..6b33a83960d2 100644
> > --- a/drivers/remoteproc/remoteproc_core.c
> > +++ b/drivers/remoteproc/remoteproc_core.c
> > @@ -1667,7 +1667,7 @@ static int rproc_stop(struct rproc *rproc, bool crashed)
> >  /*
> >   * __rproc_detach(): Does the opposite of rproc_attach()
> >   */
> > -static int __maybe_unused __rproc_detach(struct rproc *rproc)
> > +static int __rproc_detach(struct rproc *rproc)
> >  {
> >  	struct device *dev = &rproc->dev;
> >  	int ret;
> > @@ -1910,6 +1910,69 @@ void rproc_shutdown(struct rproc *rproc)
> >  }
> >  EXPORT_SYMBOL(rproc_shutdown);
> >  
> > +/**
> > + * rproc_detach() - Detach the remote processor from the
> > + * remoteproc core
> > + *
> > + * @rproc: the remote processor
> > + *
> > + * Detach a remote processor (previously attached to with rproc_actuate()).
> > + *
> > + * In case @rproc is still being used by an additional user(s), then
> > + * this function will just decrement the power refcount and exit,
> > + * without disconnecting the device.
> > + *
> > + * Function rproc_detach() calls __rproc_detach() in order to let a remote
> > + * processor know that services provided by the application processor are
> > + * no longer available.  From there it should be possible to remove the
> > + * platform driver and even power cycle the application processor (if the HW
> > + * supports it) without needing to switch off the remote processor.
> > + */
> > +int rproc_detach(struct rproc *rproc)
> > +{
> > +	struct device *dev = &rproc->dev;
> > +	int ret;
> > +
> > +	ret = mutex_lock_interruptible(&rproc->lock);
> > +	if (ret) {
> > +		dev_err(dev, "can't lock rproc %s: %d\n", rproc->name, ret);
> > +		return ret;
> > +	}
> > +
> > +	if (rproc->state != RPROC_RUNNING && rproc->state != RPROC_ATTACHED) {
> > +		ret = -EPERM;
> > +		goto out;
> > +	}
> > +
> > +	/* if the remote proc is still needed, bail out */
> > +	if (!atomic_dec_and_test(&rproc->power)) {
> > +		ret = -EBUSY;
> > +		goto out;
> > +	}
> > +
> > +	ret = __rproc_detach(rproc);
> > +	if (ret) {
> > +		atomic_inc(&rproc->power);
> > +		goto out;
> > +	}
> > +
> > +	/* clean up all acquired resources */
> > +	rproc_resource_cleanup(rproc);
> > +
> > +	rproc_disable_iommu(rproc);
> 
> I'm not an IOMMU expert,so maybe this remark is not relevant...
> As IOMMU manage the access of the remote device to its memory,
> could this lead to a remote device crash?

Right - that is the kind of thing that tormented me when I wrote this set.  On
some system it might cause a crash but on others it is needed.  As such I
decided to include it in the detach() process and let people implement the
functionality should they need to.  We can remove it but it is guaranteed that
someone will post a patch to add it again.

Based on the scenario it may have to be something like rproc_detach_iommu().
Since we have no clue on what the requirements will be I decided to simply keep
the current call.  Let me know if you really disagree with my approach.

> 
> Regards,
> Arnaud
> 
> > +
> > +	/*
> > +	 * Set the remote processor's table pointer to NULL.  Since mapping
> > +	 * of the resource table to a virtual address is done in the platform
> > +	 * driver, unmapping should also be done there.
> > +	 */
> > +	rproc->table_ptr = NULL;
> > +out:
> > +	mutex_unlock(&rproc->lock);
> > +	return ret;
> > +}
> > +EXPORT_SYMBOL(rproc_detach);
> > +
> >  /**
> >   * rproc_get_by_phandle() - find a remote processor by phandle
> >   * @phandle: phandle to the rproc
> > diff --git a/include/linux/remoteproc.h b/include/linux/remoteproc.h
> > index 3faff9bb4fb8..6713faab6959 100644
> > --- a/include/linux/remoteproc.h
> > +++ b/include/linux/remoteproc.h
> > @@ -656,6 +656,7 @@ rproc_of_resm_mem_entry_init(struct device *dev, u32 of_resm_idx, size_t len,
> >  
> >  int rproc_boot(struct rproc *rproc);
> >  void rproc_shutdown(struct rproc *rproc);
> > +int rproc_detach(struct rproc *rproc);
> >  void rproc_report_crash(struct rproc *rproc, enum rproc_crash_type type);
> >  int rproc_coredump_add_segment(struct rproc *rproc, dma_addr_t da, size_t size);
> >  int rproc_coredump_add_custom_segment(struct rproc *rproc,
> >