Hi Bjorn, Suman, and others
Do you have any comments regarding this patch?
BR
Fabien
> -----Original Message-----
> From: Fabien DESSENNE <fabien.dessenne@xxxxxx>
> Sent: mercredi 11 septembre 2019 15:57
> To: Ohad Ben-Cohen <ohad@xxxxxxxxxx>; Bjorn Andersson
> <bjorn.andersson@xxxxxxxxxx>; Suman Anna <s-anna@xxxxxx>; Jonathan Corbet
> <corbet@xxxxxxx>; linux-remoteproc@xxxxxxxxxxxxxxx; linux-
> doc@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Cc: Fabien DESSENNE <fabien.dessenne@xxxxxx>; linux-stm32@st-md-
> mailman.stormreply.com
> Subject: [PATCH v3] hwspinlock: allow sharing of hwspinlocks
>
> Allow several clients to request (hwspin_lock_request_specific()) the same lock.
> In addition to that, protect a given lock from being locked
> (hwspin_trylock{_...}()) by more that one client at a time.
>
> Since the RAW and IN_ATOMIC modes do not implement that protection (unlike
> the default, IRQ and IRQSTATE modes that make use of spin_lock{_irq,
> _irqsave}), protect __hwspin_trylock with the atomic bitop test_and_set_bit().
> This bitop is atomic (SMP-safe), does not disable neither preemption nor
> interrupts, hence it preserves the RAW and IN_ATOMIC modes constraints.
>
> Signed-off-by: Fabien Dessenne <fabien.dessenne@xxxxxx>
> ---
> Changes since v2:
> - Drop the DeviceTree-based implementation.
> - Do not let the choice between exclusive and shared usage : locks are
> always shared.
> - Add a protection (atomic bitop) working in any modes to allow safe
> sharing between clients.
>
> Changes since v1:
> - Removed useless 'status = "okay"' from stm32mp157c.dtsi
> ---
> Documentation/hwspinlock.txt | 9 ++-
> drivers/hwspinlock/hwspinlock_core.c | 98 +++++++++++++++++++++++------
> ---
> drivers/hwspinlock/hwspinlock_internal.h | 4 ++
> 3 files changed, 81 insertions(+), 30 deletions(-)
>
> diff --git a/Documentation/hwspinlock.txt b/Documentation/hwspinlock.txt index
> 6f03713..5f6f660 100644
> --- a/Documentation/hwspinlock.txt
> +++ b/Documentation/hwspinlock.txt
> @@ -53,9 +53,8 @@ Should be called from a process context (might sleep).
>
> struct hwspinlock *hwspin_lock_request_specific(unsigned int id);
>
> -Assign a specific hwspinlock id and return its address, or NULL -if that
> hwspinlock is already in use. Usually board code will -be calling this function in
> order to reserve specific hwspinlock
> +Assign a specific hwspinlock id and return its address. Usually board
> +code will be calling this function in order to reserve specific
> +hwspinlock
> ids for predefined purposes.
>
> Should be called from a process context (might sleep).
> @@ -449,11 +448,15 @@ of which represents a single hardware lock::
> * struct hwspinlock - this struct represents a single hwspinlock instance
> * @bank: the hwspinlock_device structure which owns this lock
> * @lock: initialized and used by hwspinlock core
> + * @is_locked: whether this lock is currently locked
> + * @reqcount: number of users having requested this lock
> * @priv: private data, owned by the underlying platform-specific
> hwspinlock drv
> */
> struct hwspinlock {
> struct hwspinlock_device *bank;
> spinlock_t lock;
> + unsigned long is_locked;
> + unsigned int reqcount;
> void *priv;
> };
>
> diff --git a/drivers/hwspinlock/hwspinlock_core.c
> b/drivers/hwspinlock/hwspinlock_core.c
> index 8862445..e9d3de10 100644
> --- a/drivers/hwspinlock/hwspinlock_core.c
> +++ b/drivers/hwspinlock/hwspinlock_core.c
> @@ -29,6 +29,7 @@
>
> /* radix tree tags */
> #define HWSPINLOCK_UNUSED (0) /* tags an hwspinlock as unused */
> +#define HWSPINLOCK_DYN_ASSIGN (1) /* dynamically assigned
> hwspinlock */
>
> /*
> * A radix tree is used to maintain the available hwspinlock instances.
> @@ -96,14 +97,25 @@ int __hwspin_trylock(struct hwspinlock *hwlock, int
> mode, unsigned long *flags)
> BUG_ON(!flags && mode == HWLOCK_IRQSTATE);
>
> /*
> + * Check if the lock is already taken by another context on the local
> + * cpu.
> + * Calling atomic test_and_set_bit_lock() ensures that hwspinlock is
> + * SMP-safe (so we can take it from additional contexts on the local
> + * host) in any mode, even those where we do not make use of the local
> + * spinlock.
> + */
> +
> + if (test_and_set_bit_lock(0, &hwlock->is_locked))
> + return -EBUSY;
> +
> + /*
> * This spin_lock{_irq, _irqsave} serves three purposes:
> *
> * 1. Disable preemption, in order to minimize the period of time
> * in which the hwspinlock is taken. This is important in order
> * to minimize the possible polling on the hardware interconnect
> * by a remote user of this lock.
> - * 2. Make the hwspinlock SMP-safe (so we can take it from
> - * additional contexts on the local host).
> + * 2. Make the hwspinlock SMP-safe.
> * 3. Ensure that in_atomic/might_sleep checks catch potential
> * problems with hwspinlock usage (e.g. scheduler checks like
> * 'scheduling while atomic' etc.)
> @@ -124,9 +136,9 @@ int __hwspin_trylock(struct hwspinlock *hwlock, int
> mode, unsigned long *flags)
> break;
> }
>
> - /* is lock already taken by another context on the local cpu ? */
> + /* sanity check (this shouldn't happen) */
> if (!ret)
> - return -EBUSY;
> + goto clear;
>
> /* try to take the hwspinlock device */
> ret = hwlock->bank->ops->trylock(hwlock);
> @@ -149,7 +161,7 @@ int __hwspin_trylock(struct hwspinlock *hwlock, int
> mode, unsigned long *flags)
> break;
> }
>
> - return -EBUSY;
> + goto clear;
> }
>
> /*
> @@ -165,6 +177,11 @@ int __hwspin_trylock(struct hwspinlock *hwlock, int
> mode, unsigned long *flags)
> mb();
>
> return 0;
> +
> +clear:
> + /* Clear is_locked */
> + clear_bit_unlock(0, &hwlock->is_locked);
> + return -EBUSY;
> }
> EXPORT_SYMBOL_GPL(__hwspin_trylock);
>
> @@ -299,6 +316,9 @@ void __hwspin_unlock(struct hwspinlock *hwlock, int
> mode, unsigned long *flags)
> spin_unlock(&hwlock->lock);
> break;
> }
> +
> + /* Clear is_locked set while locking */
> + clear_bit_unlock(0, &hwlock->is_locked);
> }
> EXPORT_SYMBOL_GPL(__hwspin_unlock);
>
> @@ -504,7 +524,9 @@ int hwspin_lock_register(struct hwspinlock_device *bank,
> struct device *dev,
> hwlock = &bank->lock[i];
>
> spin_lock_init(&hwlock->lock);
> + clear_bit(0, &hwlock->is_locked);
> hwlock->bank = bank;
> + hwlock->reqcount = 0;
>
> ret = hwspin_lock_register_single(hwlock, base_id + i);
> if (ret)
> @@ -664,12 +686,16 @@ static int __hwspin_lock_request(struct hwspinlock
> *hwlock)
> return ret;
> }
>
> - /* mark hwspinlock as used, should not fail */
> - tmp = radix_tree_tag_clear(&hwspinlock_tree, hwlock_to_id(hwlock),
> - HWSPINLOCK_UNUSED);
> + /* update reqcount */
> + if (!hwlock->reqcount++) {
> + /* first request, 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);
> + /* self-sanity check that should never fail */
> + WARN_ON(tmp != hwlock);
> + }
>
> return ret;
> }
> @@ -706,7 +732,7 @@ EXPORT_SYMBOL_GPL(hwspin_lock_get_id);
> */
> struct hwspinlock *hwspin_lock_request(void) {
> - struct hwspinlock *hwlock;
> + struct hwspinlock *hwlock, *tmp;
> int ret;
>
> mutex_lock(&hwspinlock_tree_lock);
> @@ -728,6 +754,13 @@ struct hwspinlock *hwspin_lock_request(void)
> if (ret < 0)
> hwlock = NULL;
>
> + /* mark this hwspinlock as dynamically assigned */
> + tmp = radix_tree_tag_set(&hwspinlock_tree, hwlock_to_id(hwlock),
> + HWSPINLOCK_DYN_ASSIGN);
> +
> + /* self-sanity check which should never fail */
> + WARN_ON(tmp != hwlock);
> +
> out:
> mutex_unlock(&hwspinlock_tree_lock);
> return hwlock;
> @@ -764,18 +797,19 @@ struct hwspinlock
> *hwspin_lock_request_specific(unsigned int id)
> /* sanity check (this shouldn't happen) */
> WARN_ON(hwlock_to_id(hwlock) != id);
>
> - /* make sure this hwspinlock is unused */
> - ret = radix_tree_tag_get(&hwspinlock_tree, id, HWSPINLOCK_UNUSED);
> - if (ret == 0) {
> - pr_warn("hwspinlock %u is already in use\n", id);
> + /* mark as used and power up */
> + ret = __hwspin_lock_request(hwlock);
> + if (ret < 0) {
> hwlock = NULL;
> goto out;
> }
>
> - /* mark as used and power up */
> - ret = __hwspin_lock_request(hwlock);
> - if (ret < 0)
> - hwlock = NULL;
> + /*
> + * warn if this lock is also used by another client which got this lock
> + * with dynamic assignment using the hwspin_lock_request() API
> + */
> + if (radix_tree_tag_get(&hwspinlock_tree, id,
> HWSPINLOCK_DYN_ASSIGN))
> + pr_warn("hwspinlock %u is shared with a 'dynamic' user\n", id);
>
> out:
> mutex_unlock(&hwspinlock_tree_lock);
> @@ -799,7 +833,7 @@ int hwspin_lock_free(struct hwspinlock *hwlock) {
> struct device *dev;
> struct hwspinlock *tmp;
> - int ret;
> + int ret, id;
>
> if (!hwlock) {
> pr_err("invalid hwlock\n");
> @@ -810,30 +844,40 @@ int hwspin_lock_free(struct hwspinlock *hwlock)
> mutex_lock(&hwspinlock_tree_lock);
>
> /* make sure the hwspinlock is used */
> - ret = radix_tree_tag_get(&hwspinlock_tree, hwlock_to_id(hwlock),
> - HWSPINLOCK_UNUSED);
> + id = hwlock_to_id(hwlock);
> + ret = radix_tree_tag_get(&hwspinlock_tree, id, HWSPINLOCK_UNUSED);
> if (ret == 1) {
> dev_err(dev, "%s: hwlock is already free\n", __func__);
> dump_stack();
> ret = -EINVAL;
> - goto out;
> + goto out_unlock;
> }
>
> /* notify the underlying device that power is not needed */
> ret = pm_runtime_put(dev);
> if (ret < 0)
> - goto out;
> + goto out_unlock;
> +
> + /* update reqcount */
> + if (--hwlock->reqcount)
> + goto out_put;
>
> /* mark this hwspinlock as available */
> - tmp = radix_tree_tag_set(&hwspinlock_tree, hwlock_to_id(hwlock),
> - HWSPINLOCK_UNUSED);
> + tmp = radix_tree_tag_set(&hwspinlock_tree, id,
> HWSPINLOCK_UNUSED);
>
> /* sanity check (this shouldn't happen) */
> WARN_ON(tmp != hwlock);
>
> + /* clear the dynamically assigned tag */
> + tmp = radix_tree_tag_clear(&hwspinlock_tree, id,
> +HWSPINLOCK_DYN_ASSIGN);
> +
> + /* self-sanity check which should never fail */
> + WARN_ON(tmp != hwlock);
> +
> +out_put:
> module_put(dev->driver->owner);
>
> -out:
> +out_unlock:
> mutex_unlock(&hwspinlock_tree_lock);
> return ret;
> }
> diff --git a/drivers/hwspinlock/hwspinlock_internal.h
> b/drivers/hwspinlock/hwspinlock_internal.h
> index 9eb6bd0..a3aae55 100644
> --- a/drivers/hwspinlock/hwspinlock_internal.h
> +++ b/drivers/hwspinlock/hwspinlock_internal.h
> @@ -35,11 +35,15 @@ struct hwspinlock_ops {
> * struct hwspinlock - this struct represents a single hwspinlock instance
> * @bank: the hwspinlock_device structure which owns this lock
> * @lock: initialized and used by hwspinlock core
> + * @is_locked: whether this lock is currently locked
> + * @reqcount: number of users having requested this lock
> * @priv: private data, owned by the underlying platform-specific hwspinlock drv
> */
> struct hwspinlock {
> struct hwspinlock_device *bank;
> spinlock_t lock;
> + unsigned long is_locked;
> + unsigned int reqcount;
> void *priv;
> };
>
> --
> 2.7.4
