xref: /linux-5.19.10/drivers/gpu/drm/drm_gem_atomic_helper.c

// SPDX-License-Identifier: GPL-2.0-or-later

#include <linux/dma-resv.h>
#include <linux/dma-fence-chain.h>

#include <drm/drm_atomic_state_helper.h>
#include <drm/drm_atomic_uapi.h>
#include <drm/drm_gem.h>
#include <drm/drm_gem_atomic_helper.h>
#include <drm/drm_gem_framebuffer_helper.h>
#include <drm/drm_simple_kms_helper.h>

#include "drm_internal.h"

/**
 * DOC: overview
 *
 * The GEM atomic helpers library implements generic atomic-commit
 * functions for drivers that use GEM objects. Currently, it provides
 * synchronization helpers, and plane state and framebuffer BO mappings
 * for planes with shadow buffers.
 *
 * Before scanout, a plane's framebuffer needs to be synchronized with
 * possible writers that draw into the framebuffer. All drivers should
 * call drm_gem_plane_helper_prepare_fb() from their implementation of
 * struct &drm_plane_helper.prepare_fb . It sets the plane's fence from
 * the framebuffer so that the DRM core can synchronize access automatically.
 *
 * drm_gem_plane_helper_prepare_fb() can also be used directly as
 * implementation of prepare_fb. For drivers based on
 * struct drm_simple_display_pipe, drm_gem_simple_display_pipe_prepare_fb()
 * provides equivalent functionality.
 *
 * .. code-block:: c
 *
 *	#include <drm/drm_gem_atomic_helper.h>
 *
 *	struct drm_plane_helper_funcs driver_plane_helper_funcs = {
 *		...,
 *		. prepare_fb = drm_gem_plane_helper_prepare_fb,
 *	};
 *
 *	struct drm_simple_display_pipe_funcs driver_pipe_funcs = {
 *		...,
 *		. prepare_fb = drm_gem_simple_display_pipe_prepare_fb,
 *	};
 *
 * A driver using a shadow buffer copies the content of the shadow buffers
 * into the HW's framebuffer memory during an atomic update. This requires
 * a mapping of the shadow buffer into kernel address space. The mappings
 * cannot be established by commit-tail functions, such as atomic_update,
 * as this would violate locking rules around dma_buf_vmap().
 *
 * The helpers for shadow-buffered planes establish and release mappings,
 * and provide struct drm_shadow_plane_state, which stores the plane's mapping
 * for commit-tail functions.
 *
 * Shadow-buffered planes can easily be enabled by using the provided macros
 * %DRM_GEM_SHADOW_PLANE_FUNCS and %DRM_GEM_SHADOW_PLANE_HELPER_FUNCS.
 * These macros set up the plane and plane-helper callbacks to point to the
 * shadow-buffer helpers.
 *
 * .. code-block:: c
 *
 *	#include <drm/drm_gem_atomic_helper.h>
 *
 *	struct drm_plane_funcs driver_plane_funcs = {
 *		...,
 *		DRM_GEM_SHADOW_PLANE_FUNCS,
 *	};
 *
 *	struct drm_plane_helper_funcs driver_plane_helper_funcs = {
 *		...,
 *		DRM_GEM_SHADOW_PLANE_HELPER_FUNCS,
 *	};
 *
 * In the driver's atomic-update function, shadow-buffer mappings are available
 * from the plane state. Use to_drm_shadow_plane_state() to upcast from
 * struct drm_plane_state.
 *
 * .. code-block:: c
 *
 *	void driver_plane_atomic_update(struct drm_plane *plane,
 *					struct drm_plane_state *old_plane_state)
 *	{
 *		struct drm_plane_state *plane_state = plane->state;
 *		struct drm_shadow_plane_state *shadow_plane_state =
 *			to_drm_shadow_plane_state(plane_state);
 *
 *		// access shadow buffer via shadow_plane_state->map
 *	}
 *
 * A mapping address for each of the framebuffer's buffer object is stored in
 * struct &drm_shadow_plane_state.map. The mappings are valid while the state
 * is being used.
 *
 * Drivers that use struct drm_simple_display_pipe can use
 * %DRM_GEM_SIMPLE_DISPLAY_PIPE_SHADOW_PLANE_FUNCS to initialize the rsp
 * callbacks. Access to shadow-buffer mappings is similar to regular
 * atomic_update.
 *
 * .. code-block:: c
 *
 *	struct drm_simple_display_pipe_funcs driver_pipe_funcs = {
 *		...,
 *		DRM_GEM_SIMPLE_DISPLAY_PIPE_SHADOW_PLANE_FUNCS,
 *	};
 *
 *	void driver_pipe_enable(struct drm_simple_display_pipe *pipe,
 *				struct drm_crtc_state *crtc_state,
 *				struct drm_plane_state *plane_state)
 *	{
 *		struct drm_shadow_plane_state *shadow_plane_state =
 *			to_drm_shadow_plane_state(plane_state);
 *
 *		// access shadow buffer via shadow_plane_state->map
 *	}
 */

/*
 * Plane Helpers
 */

/**
 * drm_gem_plane_helper_prepare_fb() - Prepare a GEM backed framebuffer
 * @plane: Plane
 * @state: Plane state the fence will be attached to
 *
 * This function extracts the exclusive fence from &drm_gem_object.resv and
 * attaches it to plane state for the atomic helper to wait on. This is
 * necessary to correctly implement implicit synchronization for any buffers
 * shared as a struct &dma_buf. This function can be used as the
 * &drm_plane_helper_funcs.prepare_fb callback.
 *
 * There is no need for &drm_plane_helper_funcs.cleanup_fb hook for simple
 * GEM based framebuffer drivers which have their buffers always pinned in
 * memory.
 *
 * This function is the default implementation for GEM drivers of
 * &drm_plane_helper_funcs.prepare_fb if no callback is provided.
 */
int drm_gem_plane_helper_prepare_fb(struct drm_plane *plane,
				    struct drm_plane_state *state)
{
	struct dma_fence *fence = dma_fence_get(state->fence);
	enum dma_resv_usage usage;
	size_t i;
	int ret;

	if (!state->fb)
		return 0;

	/*
	 * Only add the kernel fences here if there is already a fence set via
	 * explicit fencing interfaces on the atomic ioctl.
	 *
	 * This way explicit fencing can be used to overrule implicit fencing,
	 * which is important to make explicit fencing use-cases work: One
	 * example is using one buffer for 2 screens with different refresh
	 * rates. Implicit fencing will clamp rendering to the refresh rate of
	 * the slower screen, whereas explicit fence allows 2 independent
	 * render and display loops on a single buffer. If a driver allows
	 * obeys both implicit and explicit fences for plane updates, then it
	 * will break all the benefits of explicit fencing.
	 */
	usage = fence ? DMA_RESV_USAGE_KERNEL : DMA_RESV_USAGE_WRITE;

	for (i = 0; i < state->fb->format->num_planes; ++i) {
		struct drm_gem_object *obj = drm_gem_fb_get_obj(state->fb, i);
		struct dma_fence *new;

		if (WARN_ON_ONCE(!obj))
			continue;

		ret = dma_resv_get_singleton(obj->resv, usage, &new);
		if (ret)
			goto error;

		if (new && fence) {
			struct dma_fence_chain *chain = dma_fence_chain_alloc();

			if (!chain) {
				ret = -ENOMEM;
				goto error;
			}

			dma_fence_chain_init(chain, fence, new, 1);
			fence = &chain->base;

		} else if (new) {
			fence = new;
		}
	}

	dma_fence_put(state->fence);
	state->fence = fence;
	return 0;

error:
	dma_fence_put(fence);
	return ret;
}
EXPORT_SYMBOL_GPL(drm_gem_plane_helper_prepare_fb);

/**
 * drm_gem_simple_display_pipe_prepare_fb - prepare_fb helper for &drm_simple_display_pipe
 * @pipe: Simple display pipe
 * @plane_state: Plane state
 *
 * This function uses drm_gem_plane_helper_prepare_fb() to extract the fences
 * from &drm_gem_object.resv and attaches them to the plane state for the atomic
 * helper to wait on. This is necessary to correctly implement implicit
 * synchronization for any buffers shared as a struct &dma_buf. Drivers can use
 * this as their &drm_simple_display_pipe_funcs.prepare_fb callback.
 *
 * See drm_gem_plane_helper_prepare_fb() for a discussion of implicit and
 * explicit fencing in atomic modeset updates.
 */
int drm_gem_simple_display_pipe_prepare_fb(struct drm_simple_display_pipe *pipe,
					   struct drm_plane_state *plane_state)
{
	return drm_gem_plane_helper_prepare_fb(&pipe->plane, plane_state);
}
EXPORT_SYMBOL(drm_gem_simple_display_pipe_prepare_fb);

/*
 * Shadow-buffered Planes
 */

/**
 * __drm_gem_duplicate_shadow_plane_state - duplicates shadow-buffered plane state
 * @plane: the plane
 * @new_shadow_plane_state: the new shadow-buffered plane state
 *
 * This function duplicates shadow-buffered plane state. This is helpful for drivers
 * that subclass struct drm_shadow_plane_state.
 *
 * The function does not duplicate existing mappings of the shadow buffers.
 * Mappings are maintained during the atomic commit by the plane's prepare_fb
 * and cleanup_fb helpers. See drm_gem_prepare_shadow_fb() and drm_gem_cleanup_shadow_fb()
 * for corresponding helpers.
 */
void
__drm_gem_duplicate_shadow_plane_state(struct drm_plane *plane,
				       struct drm_shadow_plane_state *new_shadow_plane_state)
{
	__drm_atomic_helper_plane_duplicate_state(plane, &new_shadow_plane_state->base);
}
EXPORT_SYMBOL(__drm_gem_duplicate_shadow_plane_state);

/**
 * drm_gem_duplicate_shadow_plane_state - duplicates shadow-buffered plane state
 * @plane: the plane
 *
 * This function implements struct &drm_plane_funcs.atomic_duplicate_state for
 * shadow-buffered planes. It assumes the existing state to be of type
 * struct drm_shadow_plane_state and it allocates the new state to be of this
 * type.
 *
 * The function does not duplicate existing mappings of the shadow buffers.
 * Mappings are maintained during the atomic commit by the plane's prepare_fb
 * and cleanup_fb helpers. See drm_gem_prepare_shadow_fb() and drm_gem_cleanup_shadow_fb()
 * for corresponding helpers.
 *
 * Returns:
 * A pointer to a new plane state on success, or NULL otherwise.
 */
struct drm_plane_state *
drm_gem_duplicate_shadow_plane_state(struct drm_plane *plane)
{
	struct drm_plane_state *plane_state = plane->state;
	struct drm_shadow_plane_state *new_shadow_plane_state;

	if (!plane_state)
		return NULL;

	new_shadow_plane_state = kzalloc(sizeof(*new_shadow_plane_state), GFP_KERNEL);
	if (!new_shadow_plane_state)
		return NULL;
	__drm_gem_duplicate_shadow_plane_state(plane, new_shadow_plane_state);

	return &new_shadow_plane_state->base;
}
EXPORT_SYMBOL(drm_gem_duplicate_shadow_plane_state);

/**
 * __drm_gem_destroy_shadow_plane_state - cleans up shadow-buffered plane state
 * @shadow_plane_state: the shadow-buffered plane state
 *
 * This function cleans up shadow-buffered plane state. Helpful for drivers that
 * subclass struct drm_shadow_plane_state.
 */
void __drm_gem_destroy_shadow_plane_state(struct drm_shadow_plane_state *shadow_plane_state)
{
	__drm_atomic_helper_plane_destroy_state(&shadow_plane_state->base);
}
EXPORT_SYMBOL(__drm_gem_destroy_shadow_plane_state);

/**
 * drm_gem_destroy_shadow_plane_state - deletes shadow-buffered plane state
 * @plane: the plane
 * @plane_state: the plane state of type struct drm_shadow_plane_state
 *
 * This function implements struct &drm_plane_funcs.atomic_destroy_state
 * for shadow-buffered planes. It expects that mappings of shadow buffers
 * have been released already.
 */
void drm_gem_destroy_shadow_plane_state(struct drm_plane *plane,
					struct drm_plane_state *plane_state)
{
	struct drm_shadow_plane_state *shadow_plane_state =
		to_drm_shadow_plane_state(plane_state);

	__drm_gem_destroy_shadow_plane_state(shadow_plane_state);
	kfree(shadow_plane_state);
}
EXPORT_SYMBOL(drm_gem_destroy_shadow_plane_state);

/**
 * __drm_gem_reset_shadow_plane - resets a shadow-buffered plane
 * @plane: the plane
 * @shadow_plane_state: the shadow-buffered plane state
 *
 * This function resets state for shadow-buffered planes. Helpful
 * for drivers that subclass struct drm_shadow_plane_state.
 */
void __drm_gem_reset_shadow_plane(struct drm_plane *plane,
				  struct drm_shadow_plane_state *shadow_plane_state)
{
	__drm_atomic_helper_plane_reset(plane, &shadow_plane_state->base);
}
EXPORT_SYMBOL(__drm_gem_reset_shadow_plane);

/**
 * drm_gem_reset_shadow_plane - resets a shadow-buffered plane
 * @plane: the plane
 *
 * This function implements struct &drm_plane_funcs.reset_plane for
 * shadow-buffered planes. It assumes the current plane state to be
 * of type struct drm_shadow_plane and it allocates the new state of
 * this type.
 */
void drm_gem_reset_shadow_plane(struct drm_plane *plane)
{
	struct drm_shadow_plane_state *shadow_plane_state;

	if (plane->state) {
		drm_gem_destroy_shadow_plane_state(plane, plane->state);
		plane->state = NULL; /* must be set to NULL here */
	}

	shadow_plane_state = kzalloc(sizeof(*shadow_plane_state), GFP_KERNEL);
	if (!shadow_plane_state)
		return;
	__drm_gem_reset_shadow_plane(plane, shadow_plane_state);
}
EXPORT_SYMBOL(drm_gem_reset_shadow_plane);

/**
 * drm_gem_prepare_shadow_fb - prepares shadow framebuffers
 * @plane: the plane
 * @plane_state: the plane state of type struct drm_shadow_plane_state
 *
 * This function implements struct &drm_plane_helper_funcs.prepare_fb. It
 * maps all buffer objects of the plane's framebuffer into kernel address
 * space and stores them in &struct drm_shadow_plane_state.map. The
 * framebuffer will be synchronized as part of the atomic commit.
 *
 * See drm_gem_cleanup_shadow_fb() for cleanup.
 *
 * Returns:
 * 0 on success, or a negative errno code otherwise.
 */
int drm_gem_prepare_shadow_fb(struct drm_plane *plane, struct drm_plane_state *plane_state)
{
	struct drm_shadow_plane_state *shadow_plane_state = to_drm_shadow_plane_state(plane_state);
	struct drm_framebuffer *fb = plane_state->fb;
	int ret;

	if (!fb)
		return 0;

	ret = drm_gem_plane_helper_prepare_fb(plane, plane_state);
	if (ret)
		return ret;

	return drm_gem_fb_vmap(fb, shadow_plane_state->map, shadow_plane_state->data);
}
EXPORT_SYMBOL(drm_gem_prepare_shadow_fb);

/**
 * drm_gem_cleanup_shadow_fb - releases shadow framebuffers
 * @plane: the plane
 * @plane_state: the plane state of type struct drm_shadow_plane_state
 *
 * This function implements struct &drm_plane_helper_funcs.cleanup_fb.
 * This function unmaps all buffer objects of the plane's framebuffer.
 *
 * See drm_gem_prepare_shadow_fb() for more information.
 */
void drm_gem_cleanup_shadow_fb(struct drm_plane *plane, struct drm_plane_state *plane_state)
{
	struct drm_shadow_plane_state *shadow_plane_state = to_drm_shadow_plane_state(plane_state);
	struct drm_framebuffer *fb = plane_state->fb;

	if (!fb)
		return;

	drm_gem_fb_vunmap(fb, shadow_plane_state->map);
}
EXPORT_SYMBOL(drm_gem_cleanup_shadow_fb);

/**
 * drm_gem_simple_kms_prepare_shadow_fb - prepares shadow framebuffers
 * @pipe: the simple display pipe
 * @plane_state: the plane state of type struct drm_shadow_plane_state
 *
 * This function implements struct drm_simple_display_funcs.prepare_fb. It
 * maps all buffer objects of the plane's framebuffer into kernel address
 * space and stores them in struct drm_shadow_plane_state.map. The
 * framebuffer will be synchronized as part of the atomic commit.
 *
 * See drm_gem_simple_kms_cleanup_shadow_fb() for cleanup.
 *
 * Returns:
 * 0 on success, or a negative errno code otherwise.
 */
int drm_gem_simple_kms_prepare_shadow_fb(struct drm_simple_display_pipe *pipe,
					 struct drm_plane_state *plane_state)
{
	return drm_gem_prepare_shadow_fb(&pipe->plane, plane_state);
}
EXPORT_SYMBOL(drm_gem_simple_kms_prepare_shadow_fb);

/**
 * drm_gem_simple_kms_cleanup_shadow_fb - releases shadow framebuffers
 * @pipe: the simple display pipe
 * @plane_state: the plane state of type struct drm_shadow_plane_state
 *
 * This function implements struct drm_simple_display_funcs.cleanup_fb.
 * This function unmaps all buffer objects of the plane's framebuffer.
 *
 * See drm_gem_simple_kms_prepare_shadow_fb().
 */
void drm_gem_simple_kms_cleanup_shadow_fb(struct drm_simple_display_pipe *pipe,
					  struct drm_plane_state *plane_state)
{
	drm_gem_cleanup_shadow_fb(&pipe->plane, plane_state);
}
EXPORT_SYMBOL(drm_gem_simple_kms_cleanup_shadow_fb);

/**
 * drm_gem_simple_kms_reset_shadow_plane - resets a shadow-buffered plane
 * @pipe: the simple display pipe
 *
 * This function implements struct drm_simple_display_funcs.reset_plane
 * for shadow-buffered planes.
 */
void drm_gem_simple_kms_reset_shadow_plane(struct drm_simple_display_pipe *pipe)
{
	drm_gem_reset_shadow_plane(&pipe->plane);
}
EXPORT_SYMBOL(drm_gem_simple_kms_reset_shadow_plane);

/**
 * drm_gem_simple_kms_duplicate_shadow_plane_state - duplicates shadow-buffered plane state
 * @pipe: the simple display pipe
 *
 * This function implements struct drm_simple_display_funcs.duplicate_plane_state
 * for shadow-buffered planes. It does not duplicate existing mappings of the shadow
 * buffers. Mappings are maintained during the atomic commit by the plane's prepare_fb
 * and cleanup_fb helpers.
 *
 * Returns:
 * A pointer to a new plane state on success, or NULL otherwise.
 */
struct drm_plane_state *
drm_gem_simple_kms_duplicate_shadow_plane_state(struct drm_simple_display_pipe *pipe)
{
	return drm_gem_duplicate_shadow_plane_state(&pipe->plane);
}
EXPORT_SYMBOL(drm_gem_simple_kms_duplicate_shadow_plane_state);

/**
 * drm_gem_simple_kms_destroy_shadow_plane_state - resets shadow-buffered plane state
 * @pipe: the simple display pipe
 * @plane_state: the plane state of type struct drm_shadow_plane_state
 *
 * This function implements struct drm_simple_display_funcs.destroy_plane_state
 * for shadow-buffered planes. It expects that mappings of shadow buffers
 * have been released already.
 */
void drm_gem_simple_kms_destroy_shadow_plane_state(struct drm_simple_display_pipe *pipe,
						   struct drm_plane_state *plane_state)
{
	drm_gem_destroy_shadow_plane_state(&pipe->plane, plane_state);
}
EXPORT_SYMBOL(drm_gem_simple_kms_destroy_shadow_plane_state);