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of: property: Improve cycle detection when one of the devices is never added 

Consider this example where -> means LHS device is a consumer of RHS
device and indentation represents "child of" of the previous device.

Device A -> Device C

Device B -> Device A
	Device C

Without this commit:
1. Device A is added.
2. Device A is added to waiting for supplier list (Device C)
3. Device B is added
4. Device B is linked as a consumer to Device A
5. Device A doesn't probe because it's waiting for Device C to be added.
6. Device B doesn't probe because Device A hasn't probed.
7. Device C will never be added because it's parent hasn't probed.

So, Device A, B and C will be in a probe/add deadlock.

This commit detects this scenario and stops trying to create a device
link between Device A and Device C since doing so would create the
following cycle:
Device A -> Devic C -(parent)-> Device B -> Device A.

With this commit:
1. Device A is added.
3. Device B is added
4. Device B is linked as a consumer to Device A
5. Device A probes.
6. Device B probes because Device A has probed.
7. Device C is added and probed.

Signed-off-by: Saravana Kannan <saravanak@google.com>
Link: https://lore.kernel.org/r/20200610011934.49795-3-saravanak@google.com
Signed-off-by: Rob Herring <robh@kernel.org>
This commit is contained in:
Saravana Kannan 2020-06-09 18:19:34 -07:00 committed by Rob Herring
parent 7d34ca3854
commit bb278b149d
1 changed files with 56 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

62
drivers/of/property.c
View File

@ -1014,6 +1014,30 @@ static bool of_is_ancestor_of(struct device_node *test_ancestor,
return false;
}
/**
* of_get_next_parent_dev - Add device link to supplier from supplier phandle
* @np: device tree node
*
* Given a device tree node (@np), this function finds its closest ancestor
* device tree node that has a corresponding struct device.
*
* The caller of this function is expected to call put_device() on the returned
* device when they are done.
*/
static struct device *of_get_next_parent_dev(struct device_node *np)
{
struct device *dev = NULL;
of_node_get(np);
do {
np = of_get_next_parent(np);
if (np)
dev = get_dev_from_fwnode(&np->fwnode);
} while (np && !dev);
of_node_put(np);
return dev;
}
/**
* of_link_to_phandle - Add device link to supplier from supplier phandle
* @dev: consumer device
@ -1035,10 +1059,9 @@ static bool of_is_ancestor_of(struct device_node *test_ancestor,
static int of_link_to_phandle(struct device *dev, struct device_node *sup_np,
u32 dl_flags)
{
struct device *sup_dev;
struct device *sup_dev, *sup_par_dev;
int ret = 0;
struct device_node *tmp_np = sup_np;
int is_populated;
of_node_get(sup_np);
/*
@ -1075,16 +1098,43 @@ static int of_link_to_phandle(struct device *dev, struct device_node *sup_np,
return -EINVAL;
}
sup_dev = get_dev_from_fwnode(&sup_np->fwnode);
is_populated = of_node_check_flag(sup_np, OF_POPULATED);
of_node_put(sup_np);
if (!sup_dev && is_populated) {
if (!sup_dev && of_node_check_flag(sup_np, OF_POPULATED)) {
/* Early device without struct device. */
dev_dbg(dev, "Not linking to %pOFP - No struct device\n",
sup_np);
of_node_put(sup_np);
return -ENODEV;
} else if (!sup_dev) {
return -EAGAIN;
/*
* DL_FLAG_SYNC_STATE_ONLY doesn't block probing and supports
* cycles. So cycle detection isn't necessary and shouldn't be
* done.
*/
if (dl_flags & DL_FLAG_SYNC_STATE_ONLY) {
of_node_put(sup_np);
return -EAGAIN;
}
sup_par_dev = of_get_next_parent_dev(sup_np);
if (sup_par_dev && device_is_dependent(dev, sup_par_dev)) {
/* Cyclic dependency detected, don't try to link */
dev_dbg(dev, "Not linking to %pOFP - cycle detected\n",
sup_np);
ret = -EINVAL;
} else {
/*
* Can't check for cycles or no cycles. So let's try
* again later.
*/
ret = -EAGAIN;
}
of_node_put(sup_np);
put_device(sup_par_dev);
return ret;
}
of_node_put(sup_np);
if (!device_link_add(dev, sup_dev, dl_flags))
ret = -EINVAL;
put_device(sup_dev);