[PATCH v2 2/3] remoteproc: Introduce deny_sysfs_ops flag

[Suman Anna]

The remoteproc framework provides sysfs interfaces for changing
the firmware name and for starting/stopping a remote processor
through the sysfs files 'state' and 'firmware'. The 'recovery'
sysfs file can also be used similarly to control the error recovery
state machine of a remoteproc. These interfaces are currently
allowed irrespective of how the remoteprocs were booted (like
remoteproc self auto-boot, remoteproc client-driven boot etc).
These interfaces can adversely affect a remoteproc and its clients
especially when a remoteproc is being controlled by a remoteproc
client driver(s). Also, not all remoteproc drivers may want to
support the sysfs interfaces by default.

Add support to deny the sysfs state/firmware/recovery change by
introducing a state flag 'deny_sysfs_ops' that the individual
remoteproc drivers can set based on their usage needs. The default
behavior is to allow the sysfs operations as before.

Signed-off-by: Suman Anna <s-anna@xxxxxx>
---
v2: revised to account for the 'recovery' sysfs file as well, patch
    description updated accordingly
v1: https://patchwork.kernel.org/project/linux-remoteproc/patch/20180915003725.17549-5-s-anna@xxxxxx/

 drivers/remoteproc/remoteproc_sysfs.c | 12 ++++++++++++
 include/linux/remoteproc.h            |  2 ++
 2 files changed, 14 insertions(+)

diff --git a/drivers/remoteproc/remoteproc_sysfs.c b/drivers/remoteproc/remoteproc_sysfs.c
index bd2950a246c9..3fd18a71c188 100644
--- a/drivers/remoteproc/remoteproc_sysfs.c
+++ b/drivers/remoteproc/remoteproc_sysfs.c
@@ -49,6 +49,10 @@ static ssize_t recovery_store(struct device *dev,
 {
 	struct rproc *rproc = to_rproc(dev);
 
+	/* restrict sysfs operations if not allowed by remoteproc drivers */
+	if (rproc->deny_sysfs_ops)
+		return -EPERM;
+
 	if (sysfs_streq(buf, "enabled")) {
 		/* change the flag and begin the recovery process if needed */
 		rproc->recovery_disabled = false;
@@ -158,6 +162,10 @@ static ssize_t firmware_store(struct device *dev,
 	char *p;
 	int err, len = count;
 
+	/* restrict sysfs operations if not allowed by remoteproc drivers */
+	if (rproc->deny_sysfs_ops)
+		return -EPERM;
+
 	err = mutex_lock_interruptible(&rproc->lock);
 	if (err) {
 		dev_err(dev, "can't lock rproc %s: %d\n", rproc->name, err);
@@ -225,6 +233,10 @@ static ssize_t state_store(struct device *dev,
 	struct rproc *rproc = to_rproc(dev);
 	int ret = 0;
 
+	/* restrict sysfs operations if not allowed by remoteproc drivers */
+	if (rproc->deny_sysfs_ops)
+		return -EPERM;
+
 	if (sysfs_streq(buf, "start")) {
 		if (rproc->state == RPROC_RUNNING)
 			return -EBUSY;
diff --git a/include/linux/remoteproc.h b/include/linux/remoteproc.h
index 3fa3ba6498e8..dbc3767f7d0e 100644
--- a/include/linux/remoteproc.h
+++ b/include/linux/remoteproc.h
@@ -508,6 +508,7 @@ struct rproc_dump_segment {
  * @has_iommu: flag to indicate if remote processor is behind an MMU
  * @auto_boot: flag to indicate if remote processor should be auto-started
  * @autonomous: true if an external entity has booted the remote processor
+ * @deny_sysfs_ops: flag to not permit sysfs operations on state, firmware and recovery
  * @dump_segments: list of segments in the firmware
  * @nb_vdev: number of vdev currently handled by rproc
  * @char_dev: character device of the rproc
@@ -545,6 +546,7 @@ struct rproc {
 	bool has_iommu;
 	bool auto_boot;
 	bool autonomous;
+	bool deny_sysfs_ops;
 	struct list_head dump_segments;
 	int nb_vdev;
 	u8 elf_class;
-- 
2.28.0