/*
* Copyright (C) 2014 Red Hat
* Author: Rob Clark <robdclark@gmail.com>
*
* Permission is hereby granted, free of charge, to any person obtaining a
* copy of this software and associated documentation files (the "Software"),
* to deal in the Software without restriction, including without limitation
* the rights to use, copy, modify, merge, publish, distribute, sublicense,
* and/or sell copies of the Software, and to permit persons to whom the
* Software is furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
* OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
* ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
* OTHER DEALINGS IN THE SOFTWARE.
*/
#include <drm/drmP.h>
#include <drm/drm_crtc.h>
#include <drm/drm_modeset_lock.h>
/**
* DOC: kms locking
*
* As KMS moves toward more fine grained locking, and atomic ioctl where
* userspace can indirectly control locking order, it becomes necessary
* to use ww_mutex and acquire-contexts to avoid deadlocks. But because
* the locking is more distributed around the driver code, we want a bit
* of extra utility/tracking out of our acquire-ctx. This is provided
* by drm_modeset_lock / drm_modeset_acquire_ctx.
*
* For basic principles of ww_mutex, see: Documentation/ww-mutex-design.txt
*
* The basic usage pattern is to:
*
* drm_modeset_acquire_init(&ctx)
* retry:
* foreach (lock in random_ordered_set_of_locks) {
* ret = drm_modeset_lock(lock, &ctx)
* if (ret == -EDEADLK) {
* drm_modeset_backoff(&ctx);
* goto retry;
* }
* }
*
* ... do stuff ...
*
* drm_modeset_drop_locks(&ctx);
* drm_modeset_acquire_fini(&ctx);
*/
/**
* drm_modeset_acquire_init - initialize acquire context
* @ctx: the acquire context
* @flags: for future
*/
void drm_modeset_acquire_init(struct drm_modeset_acquire_ctx *ctx,
uint32_t flags)
{
ww_acquire_init(&ctx->ww_ctx, &crtc_ww_class);
INIT_LIST_HEAD(&ctx->locked);
}
EXPORT_SYMBOL(drm_modeset_acquire_init);
/**
* drm_modeset_acquire_fini - cleanup acquire context
* @ctx: the acquire context
*/
void drm_modeset_acquire_fini(struct drm_modeset_acquire_ctx *ctx)
{
ww_acquire_fini(&ctx->ww_ctx);
}
EXPORT_SYMBOL(drm_modeset_acquire_fini);
/**
* drm_modeset_drop_locks - drop all locks
* @ctx: the acquire context
*
* Drop all locks currently held against this acquire context.
*/
void drm_modeset_drop_locks(struct drm_modeset_acquire_ctx *ctx)
{
WARN_ON(ctx->contended);
while (!list_empty(&ctx->locked)) {
struct drm_modeset_lock *lock;
lock = list_first_entry(&ctx->locked,
struct drm_modeset_lock, head);
drm_modeset_unlock(lock);
}
}
EXPORT_SYMBOL(drm_modeset_drop_locks);
static inline int modeset_lock(struct drm_modeset_lock *lock,
struct drm_modeset_acquire_ctx *ctx,
bool interruptible, bool slow)
{
int ret;
WARN_ON(ctx->contended);
if (interruptible && slow) {
ret = ww_mutex_lock_slow_interruptible(&lock->mutex, &ctx->ww_ctx);
} else if (interruptible) {
ret = ww_mutex_lock_interruptible(&lock->mutex, &ctx->ww_ctx);
} else if (slow) {
ww_mutex_lock_slow(&lock->mutex, &ctx->ww_ctx);
ret = 0;
} else {
ret = ww_mutex_lock(&lock->mutex, &ctx->ww_ctx);
}
if (!ret) {
WARN_ON(!list_empty(&lock->head));
list_add(&lock->head, &ctx->locked);
} else if (ret == -EALREADY) {
/* we already hold the lock.. this is fine. For atomic
* we will need to be able to drm_modeset_lock() things
* without having to keep track of what is already locked
* or not.
*/
ret = 0;
} else if (ret == -EDEADLK) {
ctx->contended = lock;
}
return ret;
}
static int modeset_backoff(struct drm_modeset_acquire_ctx *ctx,
bool interruptible)
{
struct drm_modeset_lock *contended = ctx->contended;
ctx->contended = NULL;
if (WARN_ON(!contended))
return 0;
drm_modeset_drop_locks(ctx);
return modeset_lock(contended, ctx, interruptible, true);
}
/**
* drm_modeset_backoff - deadlock avoidance backoff
* @ctx: the acquire context
*
* If deadlock is detected (ie. drm_modeset_lock() returns -EDEADLK),
* you must call this function to drop all currently held locks and
* block until the contended lock becomes available.
*/
void drm_modeset_backoff(struct drm_modeset_acquire_ctx *ctx)
{
modeset_backoff(ctx, false);
}
EXPORT_SYMBOL(drm_modeset_backoff);
/**
* drm_modeset_backoff_interruptible - deadlock avoidance backoff
* @ctx: the acquire context
*
* Interruptible version of drm_modeset_backoff()
*/
int drm_modeset_backoff_interruptible(struct drm_modeset_acquire_ctx *ctx)
{
return modeset_backoff(ctx, true);
}
EXPORT_SYMBOL(drm_modeset_backoff_interruptible);
/**
* drm_modeset_lock - take modeset lock
* @lock: lock to take
* @ctx: acquire ctx
*
* If ctx is not NULL, then its ww acquire context is used and the
* lock will be tracked by the context and can be released by calling
* drm_modeset_drop_locks(). If -EDEADLK is returned, this means a
* deadlock scenario has been detected and it is an error to attempt
* to take any more locks without first calling drm_modeset_backoff().
*/
int drm_modeset_lock(struct drm_modeset_lock *lock,
struct drm_modeset_acquire_ctx *ctx)
{
if (ctx)
return modeset_lock(lock, ctx, false, false);
ww_mutex_lock(&lock->mutex, NULL);
return 0;
}
EXPORT_SYMBOL(drm_modeset_lock);
/**
* drm_modeset_lock_interruptible - take modeset lock
* @lock: lock to take
* @ctx: acquire ctx
*
* Interruptible version of drm_modeset_lock()
*/
int drm_modeset_lock_interruptible(struct drm_modeset_lock *lock,
struct drm_modeset_acquire_ctx *ctx)
{
if (ctx)
return modeset_lock(lock, ctx, true, false);
return ww_mutex_lock_interruptible(&lock->mutex, NULL);
}
EXPORT_SYMBOL(drm_modeset_lock_interruptible);
/**
* drm_modeset_unlock - drop modeset lock
* @lock: lock to release
*/
void drm_modeset_unlock(struct drm_modeset_lock *lock)
{
list_del_init(&lock->head);
ww_mutex_unlock(&lock->mutex);
}
EXPORT_SYMBOL(drm_modeset_unlock);
/* Temporary.. until we have sufficiently fine grained locking, there
* are a couple scenarios where it is convenient to grab all crtc locks.
* It is planned to remove this:
*/
int drm_modeset_lock_all_crtcs(struct drm_device *dev,
struct drm_modeset_acquire_ctx *ctx)
{
struct drm_mode_config *config = &dev->mode_config;
struct drm_crtc *crtc;
int ret = 0;
list_for_each_entry(crtc, &config->crtc_list, head) {
ret = drm_modeset_lock(&crtc->mutex, ctx);
if (ret)
return ret;
}
return 0;
}
EXPORT_SYMBOL(drm_modeset_lock_all_crtcs);