[PATCH v2 06/17] Revert "driver core: fw_devlink: Add support for batching fwnode parsing"

Saravana Kannan
2020-11-21T02:03:12Z

This reverts commit 716a7a25969003d82ab738179c3f1068a120ed11.

The fw_devlink_pause/resume() APIs added by the commit being reverted
were a first cut attempt at optimizing boot time. But these APIs don't
fully solve the problem and are very fragile (can only be used for the
top level devices being added). This series replaces them with a much
better optimization that works for all device additions and also has the
benefit of reducing the complexity of the firmware (DT, EFI) specific
code and abstracting out common code to driver core.

Signed-off-by: Saravana Kannan <saravanak@google.com>
---
drivers/base/base.h | 1 -
drivers/base/core.c | 116 +++--------------------------------------
drivers/base/dd.c | 8 ---
include/linux/fwnode.h | 2 -
4 files changed, 7 insertions(+), 120 deletions(-)

diff --git a/drivers/base/base.h b/drivers/base/base.h
index c3562adf4789..91cfb8405abd 100644
--- a/drivers/base/base.h
+++ b/drivers/base/base.h
@@ -156,7 +156,6 @@ 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;
diff --git a/drivers/base/core.c b/drivers/base/core.c
index e6bb4bf4f19d..401fa7e3505c 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -50,9 +50,6 @@ 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);
@@ -758,7 +755,7 @@ 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 || fw_devlink_is_permissive())
+ else if (ret != -ENODEV)
dev->links.need_for_probe = false;
}
mutex_unlock(&wfs_lock);
@@ -1442,116 +1439,17 @@ static void fw_devlink_link_device(struct device *dev)
{
int fw_ret;

- if (!fw_devlink_flags)
- return;
-
- 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;
+ device_link_add_missing_supplier_links();

- /*
- * 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) {
+ if (fw_devlink_flags && fwnode_has_op(dev->fwnode, add_links)) {
fw_ret = fwnode_call_int_op(dev->fwnode, add_links, dev);
- if (fw_ret == -ENODEV && fw_devlink_is_permissive())
- fw_ret = -EAGAIN;
- } else {
- fw_ret = -ENODEV;
+ 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)
- 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;
diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index b4be35fa7fda..148e81969e04 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -163,14 +163,6 @@ 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;
diff --git a/include/linux/fwnode.h b/include/linux/fwnode.h
index 9506f8ec0974..e0abafbb17f8 100644
--- a/include/linux/fwnode.h
+++ b/include/linux/fwnode.h
@@ -171,7 +171,5 @@ 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
--
2.29.2.454.gaff20da3a2-goog