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Subject[PATCH v3 3/3] DT: proc: Add runtime overlay interface in /proc
Date
Add a runtime interface to /proc to enable generic device tree overlay
usage.

Two new /proc files are added:

/proc/device-tree-overlay & /proc/device-tree-overlay-status

/proc/device-tree-overlay accepts a stream of a device tree objects and
applies it to the running kernel's device tree.

$ cat ~/BB-UART2-00A0.dtbo >device-tree-overlay
overlay_proc_release: Applied #2 overlay segments @0

/proc/device-tree-overlay-status displays the the overlays added using
the /proc interface

$ cat device-tree-overlay-status
0: 861 bytes BB-UART2:00A0

The format of the status line is
<ID>: <SIZE> bytes <part-number>:<version>

<ID> is the id of the overlay
<SIZE> is the size of the overlay in bytes
<part-number>, <version> are (optional) root level properties of the DTBO

You can remove an overlay by echoing the <ID> number of the overlay
precedded with a '-'

So
$ echo "-0" >device-tree-overlay-status

Removes the overlay.

Note that this seldom works on most platforms since platform_device
removal is something that almost never works without extra patches.

Signed-off-by: Pantelis Antoniou <panto@antoniou-consulting.com>
---
fs/proc/proc_devtree.c | 278 +++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 278 insertions(+)

diff --git a/fs/proc/proc_devtree.c b/fs/proc/proc_devtree.c
index 106a835..48f7925 100644
--- a/fs/proc/proc_devtree.c
+++ b/fs/proc/proc_devtree.c
@@ -16,6 +16,9 @@
#include <linux/slab.h>
#include <asm/prom.h>
#include <asm/uaccess.h>
+#include <linux/of_fdt.h>
+#include <linux/idr.h>
+
#include "internal.h"

static inline void set_node_proc_entry(struct device_node *np,
@@ -28,6 +31,275 @@ static inline void set_node_proc_entry(struct device_node *np,

static struct proc_dir_entry *proc_device_tree;

+#if defined(CONFIG_OF_OVERLAY)
+static struct proc_dir_entry *proc_device_tree_overlay;
+static struct proc_dir_entry *proc_device_tree_overlay_status;
+static DEFINE_MUTEX(overlay_lock);
+static DEFINE_IDR(overlay_idr);
+
+struct proc_overlay_data {
+ void *buf;
+ size_t alloc;
+ size_t size;
+
+ int id;
+ struct device_node *overlay;
+ int ovinfo_cnt;
+ struct of_overlay_info *ovinfo;
+ unsigned int failed : 1;
+ unsigned int applied : 1;
+ unsigned int removing : 1;
+};
+
+static int overlay_proc_open(struct inode *inode, struct file *file)
+{
+ struct proc_overlay_data *od;
+
+ od = kzalloc(sizeof(*od), GFP_KERNEL);
+ if (od == NULL)
+ return -ENOMEM;
+
+ od->id = -1;
+
+ /* save it */
+ file->private_data = od;
+
+ return 0;
+}
+
+static ssize_t overlay_proc_write(struct file *file, const char __user *buf, size_t size, loff_t *ppos)
+{
+ struct proc_overlay_data *od = file->private_data;
+ void *new_buf;
+
+ /* need to alloc? */
+ if (od->size + size > od->alloc) {
+
+ /* start at 256K at first */
+ if (od->alloc == 0)
+ od->alloc = SZ_256K / 2;
+
+ /* double buffer */
+ od->alloc <<= 1;
+ new_buf = kzalloc(od->alloc, GFP_KERNEL);
+ if (new_buf == NULL) {
+ pr_err("%s: failed to grow buffer\n", __func__);
+ od->failed = 1;
+ return -ENOMEM;
+ }
+
+ /* copy all we had previously */
+ memcpy(new_buf, od->buf, od->size);
+
+ /* free old buffer and assign new */
+ kfree(od->buf);
+ od->buf = new_buf;
+ }
+
+ if (unlikely(copy_from_user(od->buf + od->size, buf, size))) {
+ pr_err("%s: fault copying from userspace\n", __func__);
+ return -EFAULT;
+ }
+
+ od->size += size;
+ *ppos += size;
+
+ return size;
+}
+
+static int overlay_proc_release(struct inode *inode, struct file *file)
+{
+ struct proc_overlay_data *od = file->private_data;
+ int id;
+ int err = 0;
+
+ /* perfectly normal when not loading */
+ if (od == NULL)
+ return 0;
+
+ if (od->failed)
+ goto out_free;
+
+ of_fdt_unflatten_tree(od->buf, &od->overlay);
+ if (od->overlay == NULL) {
+ pr_err("%s: failed to unflatten tree\n", __func__);
+ err = -EINVAL;
+ goto out_free;
+ }
+ pr_debug("%s: unflattened OK\n", __func__);
+
+ /* mark it as detached */
+ of_node_set_flag(od->overlay, OF_DETACHED);
+
+ /* perform resolution */
+ err = of_resolve(od->overlay);
+ if (err != 0) {
+ pr_err("%s: Failed to resolve tree\n", __func__);
+ goto out_free;
+ }
+ pr_debug("%s: resolved OK\n", __func__);
+
+ /* now build an overlay info array */
+ err = of_build_overlay_info(od->overlay,
+ &od->ovinfo_cnt, &od->ovinfo);
+ if (err != 0) {
+ pr_err("%s: Failed to build overlay info\n", __func__);
+ goto out_free;
+ }
+
+ pr_debug("%s: built %d overlay segments\n", __func__,
+ od->ovinfo_cnt);
+
+ err = of_overlay(od->ovinfo_cnt, od->ovinfo);
+ if (err != 0) {
+ pr_err("%s: Failed to apply overlay\n", __func__);
+ goto out_free;
+ }
+
+ od->applied = 1;
+
+ mutex_lock(&overlay_lock);
+ idr_preload(GFP_KERNEL);
+ id = idr_alloc(&overlay_idr, od, 0, -1, GFP_KERNEL);
+ idr_preload_end();
+ mutex_unlock(&overlay_lock);
+
+ if (id < 0) {
+ err = id;
+ pr_err("%s: failed to get id for overlay\n", __func__);
+ goto out_free;
+ }
+ od->id = id;
+
+ pr_info("%s: Applied #%d overlay segments @%d\n", __func__,
+ od->ovinfo_cnt, od->id);
+
+ return 0;
+
+out_free:
+ if (od->id != -1)
+ idr_remove(&overlay_idr, od->id);
+ if (od->applied)
+ of_overlay_revert(od->ovinfo_cnt, od->ovinfo);
+ if (od->ovinfo)
+ of_free_overlay_info(od->ovinfo_cnt, od->ovinfo);
+ /* release memory */
+ kfree(od->buf);
+ kfree(od);
+
+ return 0;
+}
+
+static const struct file_operations overlay_proc_fops = {
+ .owner = THIS_MODULE,
+ .open = overlay_proc_open,
+ .write = overlay_proc_write,
+ .release = overlay_proc_release,
+};
+
+/*
+ * Supply data on a read from /proc/device-tree-overlay-status
+ */
+static int overlay_status_proc_show(struct seq_file *m, void *v)
+{
+ int err, id;
+ struct proc_overlay_data *od;
+ const char *part_number, *version;
+
+ rcu_read_lock();
+ idr_for_each_entry(&overlay_idr, od, id) {
+ seq_printf(m, "%d: %d bytes", id, od->size);
+ /* TODO Make this standardized? */
+ err = of_property_read_string(od->overlay, "part-number",
+ &part_number);
+ if (err != 0)
+ part_number = NULL;
+ err = of_property_read_string(od->overlay, "version",
+ &version);
+ if (err != 0)
+ version = NULL;
+ if (part_number) {
+ seq_printf(m, " %s", part_number);
+ if (version)
+ seq_printf(m, ":%s", version);
+ }
+ seq_printf(m, "\n");
+ }
+ rcu_read_unlock();
+
+ return 0;
+}
+
+static int overlay_status_proc_open(struct inode *inode, struct file *file)
+{
+ return single_open(file, overlay_status_proc_show, __PDE_DATA(inode));
+}
+
+static ssize_t overlay_status_proc_write(struct file *file, const char __user *buf,
+ size_t size, loff_t *ppos)
+{
+ struct proc_overlay_data *od;
+ char buffer[PROC_NUMBUF + 1];
+ char *ptr;
+ int id, err, count;
+
+ memset(buffer, 0, sizeof(buffer));
+ count = size;
+ if (count > sizeof(buffer) - 1)
+ count = sizeof(buffer) - 1;
+
+ if (copy_from_user(buffer, buf, count)) {
+ err = -EFAULT;
+ goto out;
+ }
+
+ ptr = buffer;
+ if (*ptr != '-') { /* only removal supported */
+ err = -EINVAL;
+ goto out;
+ }
+ ptr++;
+ err = kstrtoint(strstrip(ptr), 0, &id);
+ if (err)
+ goto out;
+
+ /* find it */
+ mutex_lock(&overlay_lock);
+ od = idr_find(&overlay_idr, id);
+ if (od == NULL) {
+ mutex_unlock(&overlay_lock);
+ err = -EINVAL;
+ goto out;
+ }
+ /* remove it */
+ idr_remove(&overlay_idr, id);
+ mutex_unlock(&overlay_lock);
+
+ err = of_overlay_revert(od->ovinfo_cnt, od->ovinfo);
+ if (err != 0) {
+ pr_err("%s: of_overlay_revert failed\n", __func__);
+ goto out;
+ }
+ /* release memory */
+ of_free_overlay_info(od->ovinfo_cnt, od->ovinfo);
+ kfree(od->buf);
+ kfree(od);
+
+ pr_info("%s: Removed overlay with id %d\n", __func__, id);
+out:
+ return err < 0 ? err : count;
+}
+
+static const struct file_operations overlay_status_proc_fops = {
+ .owner = THIS_MODULE,
+ .open = overlay_status_proc_open,
+ .read = seq_read,
+ .write = overlay_status_proc_write,
+ .llseek = seq_lseek,
+ .release = single_release,
+};
+#endif
+
/*
* Supply data on a read from /proc/device-tree/node/property.
*/
@@ -239,5 +511,11 @@ void __init proc_device_tree_init(void)
return;
}
proc_device_tree_add_node(root, proc_device_tree);
+#if defined(CONFIG_OF_OVERLAY)
+ proc_device_tree_overlay = proc_create_data("device-tree-overlay",
+ S_IWUSR, NULL, &overlay_proc_fops, NULL);
+ proc_device_tree_overlay_status = proc_create_data("device-tree-overlay-status",
+ S_IRUSR| S_IWUSR, NULL, &overlay_status_proc_fops, NULL);
+#endif
of_node_put(root);
}
--
1.7.12


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