Implement a method of applying DT quirks early in the boot sequence.
A DT quirk is a subtree of the boot DT that can be applied to
a target in the base DT resulting in a modification of the live
tree. The format of the quirk nodes is that of a device tree overlay.
For details please refer to Documentation/devicetree/quirks.txt
Signed-off-by: Pantelis Antoniou <pantelis.antoniou@xxxxxxxxxxxx>
---
Documentation/devicetree/quirks.txt | 101 ++++++++++
drivers/of/dynamic.c | 358 ++++++++++++++++++++++++++++++++++++
include/linux/of.h | 16 ++
3 files changed, 475 insertions(+)
create mode 100644 Documentation/devicetree/quirks.txt
diff --git a/Documentation/devicetree/quirks.txt b/Documentation/devicetree/quirks.txt
new file mode 100644
index 0000000..789319a
--- /dev/null
+++ b/Documentation/devicetree/quirks.txt
@@ -0,0 +1,101 @@
+A Device Tree quirk is the way which allows modification of the
+boot device tree under the control of a per-platform specific method.
+
+Take for instance the case of a board family that comprises of a
+number of different board revisions, all being incremental changes
+after an initial release.
+
+Since all board revisions must be supported via a single software image
+the only way to support this scheme is by having a different DTB for each
+revision with the bootloader selecting which one to use at boot time.
+
+While this may in theory work, in practice it is very cumbersome
+for the following reasons:
+
+1. The act of selecting a different boot device tree blob requires
+a reasonably advanced bootloader with some kind of configuration or
+scripting capabilities. Sadly this is not the case many times, the
+bootloader is extremely dumb and can only use a single dt blob.
+
+2. On many instances boot time is extremely critical; in some cases
+there are hard requirements like having working video feeds in under
+2 seconds from power-up. This leaves an extremely small time budget for
+boot-up, as low as 500ms to kernel entry. The sanest way to get there
+is by removing the standard bootloader from the normal boot sequence
+altogether by having a very small boot shim that loads the kernel and
+immediately jumps to kernel, like falcon-boot mode in u-boot does.
+
+3. Having different DTBs/DTSs for different board revisions easily leads to
+drift between versions. Since no developer is expected to have every single
+board revision at hand, things are easy to get out of sync, with board versions
+failing to boot even though the kernel is up to date.
+
+4. One final problem is the static way that device tree works.
+For example it might be desirable for various boards to have a way to
+selectively configure the boot device tree, possibly by the use of command
+line options. For instance a device might be disabled if a given command line
+option is present, different configuration to various devices for debugging
+purposes can be selected and so on. Currently the only way to do so is by
+recompiling the DTS and installing, which is an chore for developers and
+a completely unreasonable expectation from end-users.
+
+Device Tree quirks solve all those problems by having an in-kernel interface
+which per-board/platform method can use to selectively modify the device tree
+right after unflattening.
+
+A DT quirk is a subtree of the boot DT that can be applied to
+a target in the base DT resulting in a modification of the live
+tree. The format of the quirk nodes is that of a device tree overlay.
+
+As an example the following DTS contains a quirk.
+
+/ {
+ foo: foo-node {
+ bar = <10>;
+ };
+
+ select-quirk = <&quirk>;
+
+ quirk: quirk {
+ fragment@0 {
+ target = <&foo>;
+ __overlay {
+ bar = <0xf00>;
+ baz = <11>;
+ };
+ };
+ };
+};
+
+The quirk when applied would result at the following tree:
+
+/ {
+ foo: foo-node {
+ bar = <0xf00>;
+ baz = <11>;
+ };
+
+ select-quirk = <&quirk>;
+
+ quirk: quirk {
+ fragment@0 {
+ target = <&foo>;
+ __overlay {
+ bar = <0xf00>;
+ baz = <11>;
+ };
+ };
+ };
+
+};
+
+The two public method used to accomplish this are of_quirk_apply_by_node()
+and of_quirk_apply_by_phandle();
+
+To apply the quirk, a per-platform method can retrieve the phandle from the
+select-quirk property and pass it to the of_quirk_apply_by_phandle() node.
+
+The method which the per-platform method is using to select the quirk to apply
+is out of the scope of the DT quirk definition, but possible methods include
+and are not limited to: revision encoding in a GPIO input range, board id
+located in external or internal EEPROM or flash, DMI board ids, etc.
diff --git a/drivers/of/dynamic.c b/drivers/of/dynamic.c
index 3351ef4..d275dc7 100644
--- a/drivers/of/dynamic.c
+++ b/drivers/of/dynamic.c
@@ -7,6 +7,7 @@
*/
#include <linux/of.h>
+#include <linux/of_fdt.h>
#include <linux/spinlock.h>
#include <linux/slab.h>
#include <linux/string.h>
@@ -779,3 +780,360 @@ int of_changeset_action(struct of_changeset *ocs, unsigned long action,
list_add_tail(&ce->node, &ocs->entries);
return 0;
}
+
+/* fixup a symbol entry for a quirk if it exists */
+static int quirk_fixup_symbol(struct device_node *dns, struct device_node *dnp)
+{
+ struct device_node *dn;
+ struct property *prop;
+ const char *names, *namep;
+ int lens, lenp;
+ char *p;
+
+ dn = of_find_node_by_path("/__symbols__");
+ if (!dn)
+ return 0;
+
+ names = of_node_full_name(dns);
+ lens = strlen(names);
+ namep = of_node_full_name(dnp);
+ lenp = strlen(namep);
+ for_each_property_of_node(dn, prop) {
+ /* be very concervative at matching */
+ if (lens == (prop->length - 1) &&
+ ((const char *)prop->value)[prop->length] == '\0' &&
+ strcmp(prop->value, names) == 0)
+ break;
+ }
+ if (prop == NULL)
+ return 0;
+ p = early_init_dt_alloc_memory_arch(lenp + 1, __alignof__(char));
+ if (!p) {
+ pr_err("%s: symbol fixup %s failed\n", __func__, prop->name);
+ return -ENOMEM;
+ }
+ strcpy(p, namep);
+
+ pr_debug("%s: symbol fixup %s: %s -> %s\n", __func__,
+ prop->name, names, namep);
+
+ prop->value = p;
+ prop->length = lenp + 1;
+
+ return 0;
+}
+
+/* create a new quirk node */
+static struct device_node *new_quirk_node(
+ struct device_node *dns,
+ struct device_node *dnt,
+ const char *name)
+{
+ struct device_node *dnp;
+ int dnlen, len, ret;
+ struct property **pp, *prop;
+ char *p;
+
+ dnlen = strlen(dnt->full_name);
+ len = dnlen + 1 + strlen(name) + 1;
+ dnp = early_init_dt_alloc_memory_arch(
+ sizeof(struct device_node) + len,
+ __alignof__(struct device_node));
+ if (dnp == NULL) {
+ pr_err("%s: allocation failure at %pO\n", __func__,
+ dns);
+ return NULL;
+ }
+ memset(dnp, 0, sizeof(*dnp));
+ of_node_init(dnp);
+ p = (char *)dnp + sizeof(*dnp);
+
+ /* build full name */
+ dnp->full_name = p;
+ memcpy(p, dnt->full_name, dnlen);
+ p += dnlen;
+ if (dnlen != 1)
+ *p++ = '/';
+ strcpy(p, name);
+
+ dnp->parent = dnt;
+
+ /* we now move the phandle properties */
+ for (pp = &dns->properties; (prop = *pp) != NULL; ) {
+
+ /* do not touch normal properties */
+ if (strcmp(prop->name, "name") &&
+ strcmp(prop->name, "phandle") &&
+ strcmp(prop->name, "linux,phandle") &&
+ strcmp(prop->name, "ibm,phandle")) {
+ pp = &(*pp)->next;
+ continue;
+ }
+
+ /* move to the new node */
+ *pp = prop->next;
+ /* don't advance */
+
+ prop->next = dnp->properties;
+ dnp->properties = prop;
+
+ if ((strcmp(prop->name, "phandle") == 0 ||
+ strcmp(prop->name, "linux,phandle") == 0 ||
+ strcmp(prop->name, "ibm,phandle") == 0) &&
+ dnp->phandle == 0) {
+ dnp->phandle = be32_to_cpup(prop->value);
+ /* remove the phandle from the source */
+ dns->phandle = 0;
+ }
+ }
+
+ dnp->name = of_get_property(dnp, "name", NULL);
+ dnp->type = of_get_property(dnp, "device_type", NULL);
+ if (!dnp->name)
+ dnp->name = "<NULL>";
+ if (!dnp->type)
+ dnp->type = "<NULL>";
+
+ ret = quirk_fixup_symbol(dns, dnp);
+ if (ret != 0)
+ pr_warn("%s: Failed to fixup symbol %pO\n", __func__, dnp);
+
+ return dnp;
+}
+
+/* apply a quirk fragment node recursively */
+static int of_apply_quirk_fragment_node(struct device_node *dn,
+ struct device_node *dnt)
+{
+ struct property *prop, *tprop, **pp;
+ struct device_node *dnp, **dnpp, *child;
+ const char *name, *namet;
+ int i, ret;
+
+ if (!dn || !dnt)
+ return -EINVAL;
+
+ /* iterate over all properties */
+ for (pp = &dn->properties; (prop = *pp) != NULL; pp = &prop->next) {
+
+ /* do not touch auto-generated properties */
+ if (!strcmp(prop->name, "name") ||
+ !strcmp(prop->name, "phandle") ||
+ !strcmp(prop->name, "linux,phandle") ||
+ !strcmp(prop->name, "ibm,phandle") ||
+ !strcmp(prop->name, "__remove_property__") ||
+ !strcmp(prop->name, "__remove_node__"))
+ continue;
+
+ pr_debug("%s: change property %s from %pO to %pO\n",
+ __func__, prop->name, dn, dnt);
+
+ tprop = of_find_property(dnt, prop->name, NULL);
+ if (tprop) {
+ tprop->value = prop->value;
+ tprop->length = prop->length;
+ continue;
+ }
+ tprop = early_init_dt_alloc_memory_arch(
+ sizeof(struct property),
+ __alignof__(struct property));
+ if (!tprop) {
+ pr_err("%s: allocation failure at %pO\n", __func__,
+ dn);
+ return -ENOMEM;
+ }
+ tprop->name = prop->name;
+ tprop->value = prop->value;
+ tprop->length = prop->length;
+
+ /* link */
+ tprop->next = dnt->properties;
+ dnt->properties = tprop;
+ }
+
+ /* now handle property removals (if any) */
+ for (i = 0; of_property_read_string_index(dn, "__remove_property__",
+ i, &name) == 0; i++) {
+
+ /* remove property directly (we don't care about dead props) */
+ for (pp = &dnt->properties; (prop = *pp) != NULL;
+ pp = &prop->next) {
+ if (!strcmp(prop->name, name)) {
+ *pp = prop->next;
+ pr_info("%s: remove property %s at %pO\n",
+ __func__, name, dnt);
+ break;
+ }
+ }
+ }
+
+ /* now handle node removals (if any) */
+ for (i = 0; of_property_read_string_index(dn, "__remove_node__",
+ i, &name) == 0; i++) {
+
+ /* remove node directly (we don't care about dead props) */
+ for (dnpp = &dnt->child; (dnp = *dnpp) != NULL;
+ dnpp = &dnp->sibling) {
+
+ /* find path component */
+ namet = strrchr(dnp->full_name, '/');
+ if (!namet) /* root */
+ namet = dnp->full_name;
+ else
+ namet++;
+ if (!strcmp(namet, name)) {
+ *dnpp = dnp->sibling;
+ pr_info("%s: remove node %s at %pO\n",
+ __func__, namet, dnt);
+ break;
+ }
+ }
+ }
+
+ /* now iterate over childen */
+ for_each_child_of_node(dn, child) {
+ /* locate path component */
+ name = strrchr(child->full_name, '/');
+ if (name == NULL) /* root? */
+ name = child->full_name;
+ else
+ name++;
+
+ /* find node (if it exists) */
+ for (dnpp = &dnt->child; (dnp = *dnpp) != NULL;
+ dnpp = &dnp->sibling) {
+
+ namet = strrchr(dnp->full_name, '/');
+ if (!namet) /* root */
+ namet = dnp->full_name;
+ else
+ namet++;
+
+ if (!strcmp(namet, name))
+ break;
+ }
+
+ /* not found, create node */
+ if (dnp == NULL) {
+ dnp = new_quirk_node(child, dnt, name);
+ if (dnp == NULL) {
+ pr_err("%s: allocation failure at %pO\n",
+ __func__, dn);
+ of_node_put(child);
+ return -ENOMEM;
+ }
+ dnp->sibling = *dnpp;
+ *dnpp = dnp;
+
+ pr_debug("%s: new node %pO\n", __func__, dnp);
+ }
+ pr_debug("%s: recursing %pO\n", __func__, dnp);
+
+ ret = of_apply_quirk_fragment_node(child, dnp);
+ if (ret != 0) {
+ of_node_put(child);
+ return ret;
+ }
+ }
+
+ return 0;
+}
+
+/* apply a single quirk fragment located at dn */
+static int of_apply_single_quirk_fragment(struct device_node *dn)
+{
+ struct device_node *dnt, *dno;
+ const char *path;
+ u32 val;
+ int ret;
+
+ /* first try to go by using the target as a phandle */
+ dno = NULL;
+ dnt = NULL;
+ ret = of_property_read_u32(dn, "target", &val);
+ if (ret == 0)
+ dnt = of_find_node_by_phandle(val);
+
+ if (dnt == NULL) {
+ /* now try to locate by path */
+ ret = of_property_read_string(dn, "target-path",
+ &path);
+ if (ret == 0)
+ dnt = of_find_node_by_path(path);
+ }
+
+ if (dnt == NULL) {
+ pr_err("%s: Failed to find target for node %pO\n",
+ __func__, dn);
+ ret = -ENODEV;
+ goto out;
+ }
+
+ pr_debug("%s: Found target at %pO\n", __func__, dnt);
+ dno = of_get_child_by_name(dn, "__overlay__");
+ if (!dno) {
+ pr_err("%s: Failed to find overlay node %pO\n", __func__, dn);
+ ret = -ENODEV;
+ goto out;
+ }
+
+ ret = of_apply_quirk_fragment_node(dno, dnt);
+out:
+ of_node_put(dno);
+ of_node_put(dnt);
+
+ return ret;
+}
+
+/**
+ * of_quirk_apply_by_node - Apply a DT quirk found at the given node
+ *
+ * @dn: device node pointer to the quirk
+ *
+ * Returns 0 on success, a negative error value in case of an error.
+ */
+int of_quirk_apply_by_node(struct device_node *dn)
+{
+ struct device_node *child;
+ int ret;
+
+ if (!dn)
+ return -ENODEV;
+
+ pr_debug("Apply quirk at %pO\n", dn);
+
+ ret = 0;
+ for_each_child_of_node(dn, child) {
+ ret = of_apply_single_quirk_fragment(child);
+ if (ret != 0) {
+ of_node_put(child);
+ break;
+ }
+ }
+
+ return ret;
+}
+
+/**
+ * of_quirk_apply_by_node - Apply a DT quirk found by the given phandle
+ *
+ * ph: phandle of the quirk node
+ *
+ * Returns 0 on success, a negative error value in case of an error.
+ */
+int of_quirk_apply_by_phandle(phandle ph)
+{
+ struct device_node *dn;
+ int ret;
+
+ dn = of_find_node_by_phandle(ph);
+ if (!dn) {
+ pr_err("Failed to find node with phandle %u\n", ph);
+ return -ENODEV;
+ }
+
+ ret = of_quirk_apply_by_node(dn);
+ of_node_put(dn);
+
+ return ret;
+}
diff --git a/include/linux/of.h b/include/linux/of.h
index 7ede449..02d8988 100644
--- a/include/linux/of.h
+++ b/include/linux/of.h
@@ -1075,4 +1075,20 @@ static inline int of_overlay_destroy_all(void)
#endif
+/* early boot quirks */
+#ifdef CONFIG_OF_DYNAMIC
+int of_quirk_apply_by_node(struct device_node *dn);
+int of_quirk_apply_by_phandle(phandle ph);
+#else
+static inline int of_quirk_apply_by_node(struct device_node *dn)
+{
+ return -ENOTSUPP;
+}
+
+int of_quirk_apply_by_phandle(phandle ph)
+{
+ return -ENOTSUPP;
+}
+#endif
+
#endif /* _LINUX_OF_H */
--
1.7.12
--
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