On Mon, Jun 22, 2026 at 10:51:59AM +0200, Wolfram Sang wrote: > Renesas R-Car SoCs have their spinlocks inside a unit called MFIS. Up to > R-Car Gen4, there was only one MFIS unit on the SoC. Gen5, though, has > multiple instances and, thus, multiple spinlock providers. The spinlocks > are meant for specific cases (AP<->AP, AP<->RT, AP<->SCP...). For > development on these systems, it is helpful to have an overview of > registered spinlocks in debugfs. This series adds support for that. The > first two patches update the radix-tree header to support more lock > types. The third patch fixes a missing RCU annotation for the slot > pointer. The fourth patch finally adds the desired functionality. > > Because the radix tree seems to have no dedicated tree nor maintainer, I > suggest that all these patches go in via hwspinlock. This also keeps the > dependencies zero.
The radix tree is deprecated. I don't want to add any new functionality to it. Here's a replacement patch to convert hwspinlock to use an XArray instead of a radix tree. Compile tested only. >From 8ec88ed466e8153f546f7e8e69193cd5389488ee Mon Sep 17 00:00:00 2001 From: "Matthew Wilcox (Oracle)" <[email protected]> Date: Mon, 22 Jun 2026 09:38:30 -0400 Subject: [PATCH] hwspinlock: Convert to XArray The radix tree is deprecated. The XArray uses the same data structure with a nicer interface. The hwspinlock_tree_lock is not needed as the spinlock built into the XArray is sufficient for all these cases. hwspin_lock_register_single() used to always return 0. Its caller thinks it can return an errno, so I believe this to be a bug and so I have restored its ability to return an error. Signed-off-by: Matthew Wilcox (Oracle) <[email protected]> --- drivers/hwspinlock/hwspinlock_core.c | 133 ++++++++++----------------- 1 file changed, 50 insertions(+), 83 deletions(-) diff --git a/drivers/hwspinlock/hwspinlock_core.c b/drivers/hwspinlock/hwspinlock_core.c index cc8e952a6772..1dd68b8410dd 100644 --- a/drivers/hwspinlock/hwspinlock_core.c +++ b/drivers/hwspinlock/hwspinlock_core.c @@ -16,7 +16,7 @@ #include <linux/types.h> #include <linux/err.h> #include <linux/jiffies.h> -#include <linux/radix-tree.h> +#include <linux/xarray.h> #include <linux/hwspinlock.h> #include <linux/pm_runtime.h> #include <linux/mutex.h> @@ -27,34 +27,21 @@ /* retry delay used in atomic context */ #define HWSPINLOCK_RETRY_DELAY_US 100 -/* radix tree tags */ -#define HWSPINLOCK_UNUSED (0) /* tags an hwspinlock as unused */ +/* XArray search mark */ +#define HWSPINLOCK_UNUSED XA_MARK_0 /* marks a hwspinlock as unused */ /* - * A radix tree is used to maintain the available hwspinlock instances. + * An XArray is used to maintain the available hwspinlock instances. * The tree associates hwspinlock pointers with their integer key id, * and provides easy-to-use API which makes the hwspinlock core code simple * and easy to read. * - * Radix trees are quick on lookups, and reasonably efficient in terms of + * XArrays are quick on lookups, and reasonably efficient in terms of * storage, especially with high density usages such as this framework * requires (a continuous range of integer keys, beginning with zero, is - * used as the ID's of the hwspinlock instances). - * - * The radix tree API supports tagging items in the tree, which this - * framework uses to mark unused hwspinlock instances (see the - * HWSPINLOCK_UNUSED tag above). As a result, the process of querying the - * tree, looking for an unused hwspinlock instance, is now reduced to a - * single radix tree API call. - */ -static RADIX_TREE(hwspinlock_tree, GFP_KERNEL); - -/* - * Synchronization of access to the tree is achieved using this mutex, - * as the radix-tree API requires that users provide all synchronisation. - * A mutex is needed because we're using non-atomic radix tree allocations. + * used as the ID of the hwspinlock instances). */ -static DEFINE_MUTEX(hwspinlock_tree_lock); +static DEFINE_XARRAY(hwspinlocks); /** @@ -369,10 +356,9 @@ of_hwspin_lock_simple_xlate(const struct of_phandle_args *hwlock_spec) */ int of_hwspin_lock_get_id(struct device_node *np, int index) { + XA_STATE(xas, &hwspinlocks, 0); struct of_phandle_args args; struct hwspinlock *hwlock; - struct radix_tree_iter iter; - void **slot; int id; int ret; @@ -389,15 +375,9 @@ int of_hwspin_lock_get_id(struct device_node *np, int index) /* Find the hwspinlock device: we need its base_id */ ret = -EPROBE_DEFER; rcu_read_lock(); - radix_tree_for_each_slot(slot, &hwspinlock_tree, &iter, 0) { - hwlock = radix_tree_deref_slot(slot); - if (unlikely(!hwlock)) - continue; - if (radix_tree_deref_retry(hwlock)) { - slot = radix_tree_iter_retry(&iter); + xas_for_each(&xas, hwlock, ULONG_MAX) { + if (xas_retry(&xas, hwlock)) continue; - } - if (device_match_of_node(hwlock->bank->dev, args.np)) { ret = 0; break; @@ -452,51 +432,47 @@ EXPORT_SYMBOL_GPL(of_hwspin_lock_get_id_byname); static int hwspin_lock_register_single(struct hwspinlock *hwlock, int id) { - struct hwspinlock *tmp; + XA_STATE(xas, &hwspinlocks, id); + struct hwspinlock *existing; int ret; - mutex_lock(&hwspinlock_tree_lock); - - ret = radix_tree_insert(&hwspinlock_tree, id, hwlock); - if (ret) { - if (ret == -EEXIST) - pr_err("hwspinlock id %d already exists!\n", id); - goto out; + xas_lock(&xas); + existing = xas_load(&xas); + if (existing) { + pr_err("hwspinlock id %d already exists!\n", id); + xas_set_err(&xas, -EBUSY); } + xas_store(&xas, hwlock); /* mark this hwspinlock as available */ - tmp = radix_tree_tag_set(&hwspinlock_tree, id, HWSPINLOCK_UNUSED); + xas_set_mark(&xas, HWSPINLOCK_UNUSED); + ret = xas_error(&xas); + xas_unlock(&xas); - /* self-sanity check which should never fail */ - WARN_ON(tmp != hwlock); - -out: - mutex_unlock(&hwspinlock_tree_lock); - return 0; + return ret; } static struct hwspinlock *hwspin_lock_unregister_single(unsigned int id) { + XA_STATE(xas, &hwspinlocks, id); struct hwspinlock *hwlock = NULL; - int ret; + bool marked; - mutex_lock(&hwspinlock_tree_lock); + xas_lock(&xas); - /* make sure the hwspinlock is not in use (tag is set) */ - ret = radix_tree_tag_get(&hwspinlock_tree, id, HWSPINLOCK_UNUSED); - if (ret == 0) { + /* make sure the hwspinlock is not in use (mark is set) */ + marked = xas_get_mark(&xas, HWSPINLOCK_UNUSED); + if (!marked) { pr_err("hwspinlock %d still in use (or not present)\n", id); goto out; } - hwlock = radix_tree_delete(&hwspinlock_tree, id); - if (!hwlock) { - pr_err("failed to delete hwspinlock %d\n", id); - goto out; - } + hwlock = xas_store(&xas, NULL); + if (!hwlock) + pr_err("hwspinlock %d already deleted\n", id); out: - mutex_unlock(&hwspinlock_tree_lock); + xas_unlock(&xas); return hwlock; } @@ -667,19 +643,20 @@ EXPORT_SYMBOL_GPL(devm_hwspin_lock_register); /** * __hwspin_lock_request() - tag an hwspinlock as used and power it up + * @xas: XArray state * @hwlock: the target hwspinlock * * This is an internal function that prepares an hwspinlock instance * before it is given to the user. The function assumes that - * hwspinlock_tree_lock is taken. + * the xarray lock is held. * * Returns: %0 or positive to indicate success, and a negative value to * indicate an error (with the appropriate error code) */ -static int __hwspin_lock_request(struct hwspinlock *hwlock) +static int __hwspin_lock_request(struct xa_state *xas, + struct hwspinlock *hwlock) { struct device *dev = hwlock->bank->dev; - struct hwspinlock *tmp; int ret; /* prevent underlying implementation from being removed */ @@ -697,16 +674,9 @@ static int __hwspin_lock_request(struct hwspinlock *hwlock) return ret; } - ret = 0; + xas_clear_mark(xas, HWSPINLOCK_UNUSED); - /* mark hwspinlock as used, should not fail */ - tmp = radix_tree_tag_clear(&hwspinlock_tree, hwlock_to_id(hwlock), - HWSPINLOCK_UNUSED); - - /* self-sanity check that should never fail */ - WARN_ON(tmp != hwlock); - - return ret; + return 0; } /** @@ -724,13 +694,14 @@ static int __hwspin_lock_request(struct hwspinlock *hwlock) */ struct hwspinlock *hwspin_lock_request_specific(unsigned int id) { + XA_STATE(xas, &hwspinlocks, id); struct hwspinlock *hwlock; int ret; - mutex_lock(&hwspinlock_tree_lock); + xas_lock(&xas); /* make sure this hwspinlock exists */ - hwlock = radix_tree_lookup(&hwspinlock_tree, id); + hwlock = xas_load(&xas); if (!hwlock) { pr_warn("hwspinlock %u does not exist\n", id); goto out; @@ -740,7 +711,7 @@ struct hwspinlock *hwspin_lock_request_specific(unsigned int id) WARN_ON(hwlock_to_id(hwlock) != id); /* make sure this hwspinlock is unused */ - ret = radix_tree_tag_get(&hwspinlock_tree, id, HWSPINLOCK_UNUSED); + ret = xas_get_mark(&xas, HWSPINLOCK_UNUSED); if (ret == 0) { pr_warn("hwspinlock %u is already in use\n", id); hwlock = NULL; @@ -748,12 +719,12 @@ struct hwspinlock *hwspin_lock_request_specific(unsigned int id) } /* mark as used and power up */ - ret = __hwspin_lock_request(hwlock); + ret = __hwspin_lock_request(&xas, hwlock); if (ret < 0) hwlock = NULL; out: - mutex_unlock(&hwspinlock_tree_lock); + xas_unlock(&xas); return hwlock; } EXPORT_SYMBOL_GPL(hwspin_lock_request_specific); @@ -772,8 +743,8 @@ EXPORT_SYMBOL_GPL(hwspin_lock_request_specific); */ int hwspin_lock_free(struct hwspinlock *hwlock) { + XA_STATE(xas, &hwspinlocks, 0); struct device *dev; - struct hwspinlock *tmp; int ret; if (!hwlock) { @@ -782,11 +753,11 @@ int hwspin_lock_free(struct hwspinlock *hwlock) } dev = hwlock->bank->dev; - mutex_lock(&hwspinlock_tree_lock); + xas_lock(&xas); + xas_set(&xas, hwlock_to_id(hwlock)); /* make sure the hwspinlock is used */ - ret = radix_tree_tag_get(&hwspinlock_tree, hwlock_to_id(hwlock), - HWSPINLOCK_UNUSED); + ret = xas_get_mark(&xas, HWSPINLOCK_UNUSED); if (ret == 1) { dev_err(dev, "%s: hwlock is already free\n", __func__); dump_stack(); @@ -798,16 +769,12 @@ int hwspin_lock_free(struct hwspinlock *hwlock) pm_runtime_put(dev); /* mark this hwspinlock as available */ - tmp = radix_tree_tag_set(&hwspinlock_tree, hwlock_to_id(hwlock), - HWSPINLOCK_UNUSED); - - /* sanity check (this shouldn't happen) */ - WARN_ON(tmp != hwlock); + xas_set_mark(&xas, HWSPINLOCK_UNUSED); module_put(dev->driver->owner); out: - mutex_unlock(&hwspinlock_tree_lock); + xas_unlock(&xas); return ret; } EXPORT_SYMBOL_GPL(hwspin_lock_free); -- 2.47.3
