drm_exec.c | Explore in Territory

// SPDX-License-Identifier: GPL-2.0 OR MIT

#include <drm/drm_exec.h>
#include <drm/drm_gem.h>
#include <linux/dma-resv.h>

/**
 * DOC: Overview
 *
 * This component mainly abstracts the retry loop necessary for locking
 * multiple GEM objects while preparing hardware operations (e.g. command
 * submissions, page table updates etc..).
 *
 * If a contention is detected while locking a GEM object the cleanup procedure
 * unlocks all previously locked GEM objects and locks the contended one first
 * before locking any further objects.
 *
 * After an object is locked fences slots can optionally be reserved on the
 * dma_resv object inside the GEM object.
 *
 * A typical usage pattern should look like this::
 *
 *	struct drm_gem_object *obj;
 *	struct drm_exec exec;
 *	unsigned long index;
 *	int ret;
 *
 *	drm_exec_init(&exec, DRM_EXEC_INTERRUPTIBLE_WAIT);
 *	drm_exec_until_all_locked(&exec) {
 *		ret = drm_exec_prepare_obj(&exec, boA, 1);
 *		drm_exec_retry_on_contention(&exec);
 *		if (ret)
 *			goto error;
 *
 *		ret = drm_exec_prepare_obj(&exec, boB, 1);
 *		drm_exec_retry_on_contention(&exec);
 *		if (ret)
 *			goto error;
 *	}
 *
 *	drm_exec_for_each_locked_object(&exec, index, obj) {
 *		dma_resv_add_fence(obj->resv, fence, DMA_RESV_USAGE_READ);
 *		...
 *	}
 *	drm_exec_fini(&exec);
 *
 * See struct dma_exec for more details.
 */

/* Dummy value used to initially enter the retry loop */
#define DRM_EXEC_DUMMY …

/* Unlock all objects and drop references */
static void drm_exec_unlock_all(struct drm_exec *exec)
{ … }

/**
 * drm_exec_init - initialize a drm_exec object
 * @exec: the drm_exec object to initialize
 * @flags: controls locking behavior, see DRM_EXEC_* defines
 * @nr: the initial # of objects
 *
 * Initialize the object and make sure that we can track locked objects.
 *
 * If nr is non-zero then it is used as the initial objects table size.
 * In either case, the table will grow (be re-allocated) on demand.
 */
void drm_exec_init(struct drm_exec *exec, u32 flags, unsigned nr)
{ … }
EXPORT_SYMBOL(…);

/**
 * drm_exec_fini - finalize a drm_exec object
 * @exec: the drm_exec object to finalize
 *
 * Unlock all locked objects, drop the references to objects and free all memory
 * used for tracking the state.
 */
void drm_exec_fini(struct drm_exec *exec)
{ … }
EXPORT_SYMBOL(…);

/**
 * drm_exec_cleanup - cleanup when contention is detected
 * @exec: the drm_exec object to cleanup
 *
 * Cleanup the current state and return true if we should stay inside the retry
 * loop, false if there wasn't any contention detected and we can keep the
 * objects locked.
 */
bool drm_exec_cleanup(struct drm_exec *exec)
{ … }
EXPORT_SYMBOL(…);

/* Track the locked object in the array */
static int drm_exec_obj_locked(struct drm_exec *exec,
			       struct drm_gem_object *obj)
{ … }

/* Make sure the contended object is locked first */
static int drm_exec_lock_contended(struct drm_exec *exec)
{ … }

/**
 * drm_exec_lock_obj - lock a GEM object for use
 * @exec: the drm_exec object with the state
 * @obj: the GEM object to lock
 *
 * Lock a GEM object for use and grab a reference to it.
 *
 * Returns: -EDEADLK if a contention is detected, -EALREADY when object is
 * already locked (can be suppressed by setting the DRM_EXEC_IGNORE_DUPLICATES
 * flag), -ENOMEM when memory allocation failed and zero for success.
 */
int drm_exec_lock_obj(struct drm_exec *exec, struct drm_gem_object *obj)
{ … }
EXPORT_SYMBOL(…);

/**
 * drm_exec_unlock_obj - unlock a GEM object in this exec context
 * @exec: the drm_exec object with the state
 * @obj: the GEM object to unlock
 *
 * Unlock the GEM object and remove it from the collection of locked objects.
 * Should only be used to unlock the most recently locked objects. It's not time
 * efficient to unlock objects locked long ago.
 */
void drm_exec_unlock_obj(struct drm_exec *exec, struct drm_gem_object *obj)
{ … }
EXPORT_SYMBOL(…);

/**
 * drm_exec_prepare_obj - prepare a GEM object for use
 * @exec: the drm_exec object with the state
 * @obj: the GEM object to prepare
 * @num_fences: how many fences to reserve
 *
 * Prepare a GEM object for use by locking it and reserving fence slots.
 *
 * Returns: -EDEADLK if a contention is detected, -EALREADY when object is
 * already locked, -ENOMEM when memory allocation failed and zero for success.
 */
int drm_exec_prepare_obj(struct drm_exec *exec, struct drm_gem_object *obj,
			 unsigned int num_fences)
{ … }
EXPORT_SYMBOL(…);

/**
 * drm_exec_prepare_array - helper to prepare an array of objects
 * @exec: the drm_exec object with the state
 * @objects: array of GEM object to prepare
 * @num_objects: number of GEM objects in the array
 * @num_fences: number of fences to reserve on each GEM object
 *
 * Prepares all GEM objects in an array, aborts on first error.
 * Reserves @num_fences on each GEM object after locking it.
 *
 * Returns: -EDEADLOCK on contention, -EALREADY when object is already locked,
 * -ENOMEM when memory allocation failed and zero for success.
 */
int drm_exec_prepare_array(struct drm_exec *exec,
			   struct drm_gem_object **objects,
			   unsigned int num_objects,
			   unsigned int num_fences)
{ … }
EXPORT_SYMBOL(…);

MODULE_DESCRIPTION(…) …;
MODULE_LICENSE(…) …;
linux/drivers/gpu/drm/drm_exec.c
