[PATCH v4 1/2] remoteproc: Introduce deny_sysfs_ops flag

[Puranjay Mohan <p-mohan@xxxxxx>]

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.

Implement attribute_group->is_visible() to hide the sysfs
state/firmware/recovery entries when deny_sysfs_ops flag is set.

Signed-off-by: Puranjay Mohan <p-mohan@xxxxxx>
---
Changes in v3->v4:
Use mode = 0444 in rproc_is_visible() to make the sysfs entries
read-only when the deny_sysfs_ops flag is set.
---
 drivers/remoteproc/remoteproc_sysfs.c | 18 +++++++++++++++++-
 include/linux/remoteproc.h            |  2 ++
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/drivers/remoteproc/remoteproc_sysfs.c b/drivers/remoteproc/remoteproc_sysfs.c
index ea8b89f97d7b..da2d0eecfa44 100644
--- a/drivers/remoteproc/remoteproc_sysfs.c
+++ b/drivers/remoteproc/remoteproc_sysfs.c
@@ -230,6 +230,21 @@ static ssize_t name_show(struct device *dev, struct device_attribute *attr,
 }
 static DEVICE_ATTR_RO(name);
 
+static umode_t rproc_is_visible(struct kobject *kobj, struct attribute *attr,
+				int n)
+{
+	struct device *dev = kobj_to_dev(kobj);
+	struct rproc *rproc = to_rproc(dev);
+	umode_t mode = attr->mode;
+
+	if (rproc->deny_sysfs_ops && (attr == &dev_attr_recovery.attr ||
+				      attr == &dev_attr_firmware.attr ||
+				      attr == &dev_attr_state.attr))
+		mode = 0444;
+
+	return mode;
+}
+
 static struct attribute *rproc_attrs[] = {
 	&dev_attr_coredump.attr,
 	&dev_attr_recovery.attr,
@@ -240,7 +255,8 @@ static struct attribute *rproc_attrs[] = {
 };
 
 static const struct attribute_group rproc_devgroup = {
-	.attrs = rproc_attrs
+	.attrs = rproc_attrs,
+	.is_visible = rproc_is_visible,
 };
 
 static const struct attribute_group *rproc_devgroups[] = {
diff --git a/include/linux/remoteproc.h b/include/linux/remoteproc.h
index e0600e1e5c17..3849c66ce38f 100644
--- a/include/linux/remoteproc.h
+++ b/include/linux/remoteproc.h
@@ -523,6 +523,7 @@ struct rproc_dump_segment {
  * @table_sz: size of @cached_table
  * @has_iommu: flag to indicate if remote processor is behind an MMU
  * @auto_boot: flag to indicate if remote processor should be auto-started
+ * @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
  * @elf_class: firmware ELF class
@@ -562,6 +563,7 @@ struct rproc {
 	size_t table_sz;
 	bool has_iommu;
 	bool auto_boot;
+	bool deny_sysfs_ops;
 	struct list_head dump_segments;
 	int nb_vdev;
 	u8 elf_class;
-- 
2.17.1