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

[Arnaud POULIQUEN <arnaud.pouliquen@st.com>]

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?

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,
>