rpmsg: Add driver_override device attribute for rpmsg_device

This patch adds "driver_override" device attribute for rpmsg_device which
will allow users to explicitly specify the rpmsg_driver to be used via
sysfs entry.

The "driver_override" device attribute implemented here is very similar
to "driver_override" implemented for platform, pci, and amba bus types.

One important use-case of "driver_override" device attribute is to force
use of rpmsg_chrdev driver for certain rpmsg_device instances.

Signed-off-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

2 files changed, 59 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-bus-rpmsg b/Documentation/ABI/testing/sysfs-bus-rpmsg
index 189e419a5a2d..990fcc420935 100644
--- a/Documentation/ABI/testing/sysfs-bus-rpmsg
+++ b/Documentation/ABI/testing/sysfs-bus-rpmsg
@@ -73,3 +73,23 @@ Description:
                 This sysfs entry tells us whether the channel is a local
                 server channel that is announced (values are either
                 true or false).
+
+What:           /sys/bus/rpmsg/devices/.../driver_override
+Date:           April 2018
+KernelVersion:  4.18
+Contact:        Bjorn Andersson <bjorn.andersson@linaro.org>
+Description:
+                Every rpmsg device is a communication channel with a remote
+                processor. Channels are identified by a textual name (see
+                /sys/bus/rpmsg/devices/.../name above) and have a local
+                ("source") rpmsg address, and remote ("destination") rpmsg
+                address.
+
+                The listening entity (or client) which communicates with a
+                remote processor is referred as rpmsg driver. The rpmsg device
+                and rpmsg driver are matched based on rpmsg device name and
+                rpmsg driver ID table.
+
+                This sysfs entry allows the rpmsg driver for a rpmsg device
+                to be specified which will override standard OF, ID table
+                and name matching.
diff --git a/drivers/rpmsg/rpmsg_core.c b/drivers/rpmsg/rpmsg_core.c
index 920a02f0462c..bea7c74e12eb 100644
--- a/drivers/rpmsg/rpmsg_core.c
+++ b/drivers/rpmsg/rpmsg_core.c
@@ -333,11 +333,49 @@ field##_show(struct device *dev,					\
 }                                                                       \
 static DEVICE_ATTR_RO(field);
 
+#define rpmsg_string_attr(field, member)                                \
+static ssize_t                                                          \
+field##_store(struct device *dev, struct device_attribute *attr,        \
+              const char *buf, size_t sz)                               \
+{                                                                       \
+        struct rpmsg_device *rpdev = to_rpmsg_device(dev);              \
+        char *new, *old;                                                \
+                                                                        \
+        new = kstrndup(buf, sz, GFP_KERNEL);                            \
+        if (!new)                                                       \
+                return -ENOMEM;                                         \
+        new[strcspn(new, "\n")] = '\0';                                 \
+                                                                        \
+        device_lock(dev);                                               \
+        old = rpdev->member;                                            \
+        if (strlen(new)) {                                              \
+                rpdev->member = new;                                    \
+        } else {                                                        \
+                kfree(new);                                             \
+                rpdev->member = NULL;                                   \
+        }                                                               \
+        device_unlock(dev);                                             \
+                                                                        \
+        kfree(old);                                                     \
+                                                                        \
+        return sz;                                                      \
+}                                                                       \
+static ssize_t                                                          \
+field##_show(struct device *dev,                                        \
+             struct device_attribute *attr, char *buf)                  \
+{                                                                       \
+        struct rpmsg_device *rpdev = to_rpmsg_device(dev);              \
+                                                                        \
+        return sprintf(buf, "%s\n", rpdev->member);                     \
+}                                                                       \
+static DEVICE_ATTR_RW(field)
+
 /* for more info, see Documentation/ABI/testing/sysfs-bus-rpmsg */
 rpmsg_show_attr(name, id.name, "%s\n");
 rpmsg_show_attr(src, src, "0x%x\n");
 rpmsg_show_attr(dst, dst, "0x%x\n");
 rpmsg_show_attr(announce, announce ? "true" : "false", "%s\n");
+rpmsg_string_attr(driver_override, driver_override);
 
 static ssize_t modalias_show(struct device *dev,
                              struct device_attribute *attr, char *buf)
@@ -359,6 +397,7 @@ static struct attribute *rpmsg_dev_attrs[] = {
         &dev_attr_dst.attr,
         &dev_attr_src.attr,
         &dev_attr_announce.attr,
+        &dev_attr_driver_override.attr,
         NULL,
 };
 ATTRIBUTE_GROUPS(rpmsg_dev);