driver core: fw_devlink: Add support for batching fwnode parsing

The amount of time spent parsing fwnodes of devices can become really
high if the devices are added in an non-ideal order. Worst case can be
O(N^2) when N devices are added. But this can be optimized to O(N) by
adding all the devices and then parsing all their fwnodes in one batch.

This commit adds fw_devlink_pause() and fw_devlink_resume() to allow
doing this.

Signed-off-by: Saravana Kannan <saravanak@google.com>
Link: https://lore.kernel.org/r/20200515053500.215929-4-saravanak@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Saravana Kannan 2020-05-14 22:34:59 -07:00 committed by Greg Kroah-Hartman
parent 5f5377eadd
commit 716a7a2596
4 changed files with 120 additions and 7 deletions

View File

@ -153,6 +153,7 @@ extern char *make_class_name(const char *name, struct kobject *kobj);
extern int devres_release_all(struct device *dev);
extern void device_block_probing(void);
extern void device_unblock_probing(void);
extern void driver_deferred_probe_force_trigger(void);
/* /sys/devices directory */
extern struct kset *devices_kset;

View File

@ -49,6 +49,9 @@ static LIST_HEAD(wait_for_suppliers);
static DEFINE_MUTEX(wfs_lock);
static LIST_HEAD(deferred_sync);
static unsigned int defer_sync_state_count = 1;
static unsigned int defer_fw_devlink_count;
static DEFINE_MUTEX(defer_fw_devlink_lock);
static bool fw_devlink_is_permissive(void);
#ifdef CONFIG_SRCU
static DEFINE_MUTEX(device_links_lock);
@ -527,7 +530,7 @@ static void device_link_add_missing_supplier_links(void)
int ret = fwnode_call_int_op(dev->fwnode, add_links, dev);
if (!ret)
list_del_init(&dev->links.needs_suppliers);
else if (ret != -ENODEV)
else if (ret != -ENODEV || fw_devlink_is_permissive())
dev->links.need_for_probe = false;
}
mutex_unlock(&wfs_lock);
@ -1177,17 +1180,116 @@ static void fw_devlink_link_device(struct device *dev)
{
int fw_ret;
device_link_add_missing_supplier_links();
if (!fw_devlink_flags)
return;
if (fw_devlink_flags && fwnode_has_op(dev->fwnode, add_links)) {
mutex_lock(&defer_fw_devlink_lock);
if (!defer_fw_devlink_count)
device_link_add_missing_supplier_links();
/*
* The device's fwnode not having add_links() doesn't affect if other
* consumers can find this device as a supplier. So, this check is
* intentionally placed after device_link_add_missing_supplier_links().
*/
if (!fwnode_has_op(dev->fwnode, add_links))
goto out;
/*
* If fw_devlink is being deferred, assume all devices have mandatory
* suppliers they need to link to later. Then, when the fw_devlink is
* resumed, all these devices will get a chance to try and link to any
* suppliers they have.
*/
if (!defer_fw_devlink_count) {
fw_ret = fwnode_call_int_op(dev->fwnode, add_links, dev);
if (fw_ret == -ENODEV && !fw_devlink_is_permissive())
device_link_wait_for_mandatory_supplier(dev);
else if (fw_ret)
device_link_wait_for_optional_supplier(dev);
if (fw_ret == -ENODEV && fw_devlink_is_permissive())
fw_ret = -EAGAIN;
} else {
fw_ret = -ENODEV;
}
if (fw_ret == -ENODEV)
device_link_wait_for_mandatory_supplier(dev);
else if (fw_ret)
device_link_wait_for_optional_supplier(dev);
out:
mutex_unlock(&defer_fw_devlink_lock);
}
/**
* fw_devlink_pause - Pause parsing of fwnode to create device links
*
* Calling this function defers any fwnode parsing to create device links until
* fw_devlink_resume() is called. Both these functions are ref counted and the
* caller needs to match the calls.
*
* While fw_devlink is paused:
* - Any device that is added won't have its fwnode parsed to create device
* links.
* - The probe of the device will also be deferred during this period.
* - Any devices that were already added, but waiting for suppliers won't be
* able to link to newly added devices.
*
* Once fw_devlink_resume():
* - All the fwnodes that was not parsed will be parsed.
* - All the devices that were deferred probing will be reattempted if they
* aren't waiting for any more suppliers.
*
* This pair of functions, is mainly meant to optimize the parsing of fwnodes
* when a lot of devices that need to link to each other are added in a short
* interval of time. For example, adding all the top level devices in a system.
*
* For example, if N devices are added and:
* - All the consumers are added before their suppliers
* - All the suppliers of the N devices are part of the N devices
*
* Then:
*
* - With the use of fw_devlink_pause() and fw_devlink_resume(), each device
* will only need one parsing of its fwnode because it is guaranteed to find
* all the supplier devices already registered and ready to link to. It won't
* have to do another pass later to find one or more suppliers it couldn't
* find in the first parse of the fwnode. So, we'll only need O(N) fwnode
* parses.
*
* - Without the use of fw_devlink_pause() and fw_devlink_resume(), we would
* end up doing O(N^2) parses of fwnodes because every device that's added is
* guaranteed to trigger a parse of the fwnode of every device added before
* it. This O(N^2) parse is made worse by the fact that when a fwnode of a
* device is parsed, all it descendant devices might need to have their
* fwnodes parsed too (even if the devices themselves aren't added).
*/
void fw_devlink_pause(void)
{
mutex_lock(&defer_fw_devlink_lock);
defer_fw_devlink_count++;
mutex_unlock(&defer_fw_devlink_lock);
}
/** fw_devlink_resume - Resume parsing of fwnode to create device links
*
* This function is used in conjunction with fw_devlink_pause() and is ref
* counted. See documentation for fw_devlink_pause() for more details.
*/
void fw_devlink_resume(void)
{
mutex_lock(&defer_fw_devlink_lock);
if (!defer_fw_devlink_count) {
WARN(true, "Unmatched fw_devlink pause/resume!");
goto out;
}
defer_fw_devlink_count--;
if (defer_fw_devlink_count)
goto out;
device_link_add_missing_supplier_links();
driver_deferred_probe_force_trigger();
out:
mutex_unlock(&defer_fw_devlink_lock);
}
/* Device links support end. */
int (*platform_notify)(struct device *dev) = NULL;

View File

@ -160,6 +160,14 @@ static bool driver_deferred_probe_enable = false;
* again.
*/
static void driver_deferred_probe_trigger(void)
{
if (!driver_deferred_probe_enable)
return;
driver_deferred_probe_force_trigger();
}
void driver_deferred_probe_force_trigger(void)
{
if (!driver_deferred_probe_enable)
return;

View File

@ -171,5 +171,7 @@ struct fwnode_operations {
#define get_dev_from_fwnode(fwnode) get_device((fwnode)->dev)
extern u32 fw_devlink_get_flags(void);
void fw_devlink_pause(void);
void fw_devlink_resume(void);
#endif