[PATCH v5 12/19] remoteproc: Introduce function rproc_detach()

[Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>]

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@xxxxxxxxxx>
---
New for V5:
- Fixed comment about rproc_actuate() that no longer exists.
- Added call to rproc_unprepare_device() to balance rproc_prepare_device() in
  function rproc_attach().
- Removed RB from Peng and Arnaud because of the above.
---
 drivers/remoteproc/remoteproc_core.c | 66 +++++++++++++++++++++++++++-
 include/linux/remoteproc.h           |  1 +
 2 files changed, 66 insertions(+), 1 deletion(-)

diff --git a/drivers/remoteproc/remoteproc_core.c b/drivers/remoteproc/remoteproc_core.c
index b150138542d4..660dcc002ff6 100644
--- a/drivers/remoteproc/remoteproc_core.c
+++ b/drivers/remoteproc/remoteproc_core.c
@@ -1712,7 +1712,7 @@ 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;
@@ -1954,6 +1954,70 @@ 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_attach()).
+ *
+ * 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);
+
+	/* release HW resources if needed */
+	rproc_unprepare_device(rproc);
+
+	rproc_disable_iommu(rproc);
+
+	/* Follow the same sequence as in rproc_shutdown() */
+	kfree(rproc->cached_table);
+	rproc->cached_table = NULL;
+	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 eff55ec72e80..e1c843c19cc6 100644
--- a/include/linux/remoteproc.h
+++ b/include/linux/remoteproc.h
@@ -662,6 +662,7 @@ 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);
 int rproc_set_firmware(struct rproc *rproc, const char *fw_name);
 void rproc_report_crash(struct rproc *rproc, enum rproc_crash_type type);
 void rproc_coredump_using_sections(struct rproc *rproc);
-- 
2.25.1