drm/suballoc: Extract amdgpu_sa.c as generic suballocation helper

Suballocating a buffer object is something that is not driver-specific
and useful for many drivers.

Use a slightly modified version of amdgpu_sa.c

v2:
- Style cleanups.
- Added / Modified documentation.
- Use u64 for the sizes and offset. The code dates back to 2012 and
  using unsigned int will probably soon come back to bite us.
  We can consider size_t as well for better 32-bit efficiency.
- Add and document gfp, intr and align arguments to drm_suballoc_new().
- Use drm_printer for debug output.

v3:
- Remove stale author info (Christian König)

v4:
- Avoid 64-bit integer divisions (kernel test robot <lkp@intel.com>)
- Use size_t rather than u64 for the managed range. (Thomas)
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Co-developed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Acked-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Acked-by: Alex Deucher <alexdeucher@gmail.com>
Acked-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230224095152.30134-2-thomas.hellstrom@linux.intel.com

drivers/gpu/drm/Kconfig

@@ -231,6 +231,10 @@ config DRM_GEM_SHMEM_HELPER
 	help
 	  Choose this if you need the GEM shmem helper functions
 
+config DRM_SUBALLOC_HELPER
+	tristate
+	depends on DRM
+
 config DRM_SCHED
 	tristate
 	depends on DRM

drivers/gpu/drm/Makefile

@@ -88,6 +88,9 @@ obj-$(CONFIG_DRM_GEM_DMA_HELPER) += drm_dma_helper.o
 drm_shmem_helper-y := drm_gem_shmem_helper.o
 obj-$(CONFIG_DRM_GEM_SHMEM_HELPER) += drm_shmem_helper.o
 
+drm_suballoc_helper-y := drm_suballoc.o
+obj-$(CONFIG_DRM_SUBALLOC_HELPER) += drm_suballoc_helper.o
+
 drm_vram_helper-y := drm_gem_vram_helper.o
 obj-$(CONFIG_DRM_VRAM_HELPER) += drm_vram_helper.o
 

include/drm/drm_suballoc.h

+/* SPDX-License-Identifier: GPL-2.0 OR MIT */
+/*
+ * Copyright 2011 Red Hat Inc.
+ * Copyright © 2022 Intel Corporation
+ */
+#ifndef _DRM_SUBALLOC_H_
+#define _DRM_SUBALLOC_H_
+
+#include <drm/drm_mm.h>
+
+#include <linux/dma-fence.h>
+#include <linux/types.h>
+
+#define DRM_SUBALLOC_MAX_QUEUES 32
+/**
+ * struct drm_suballoc_manager - fenced range allocations
+ * @wq: Wait queue for sleeping allocations on contention.
+ * @hole: Pointer to first hole node.
+ * @olist: List of allocated ranges.
+ * @flist: Array[fence context hash] of queues of fenced allocated ranges.
+ * @size: Size of the managed range.
+ * @align: Default alignment for the managed range.
+ */
+struct drm_suballoc_manager {
+	wait_queue_head_t wq;
+	struct list_head *hole;
+	struct list_head olist;
+	struct list_head flist[DRM_SUBALLOC_MAX_QUEUES];
+	size_t size;
+	size_t align;
+};
+
+/**
+ * struct drm_suballoc - Sub-allocated range
+ * @olist: List link for list of allocated ranges.
+ * @flist: List linkk for the manager fenced allocated ranges queues.
+ * @manager: The drm_suballoc_manager.
+ * @soffset: Start offset.
+ * @eoffset: End offset + 1 so that @eoffset - @soffset = size.
+ * @dma_fence: The fence protecting the allocation.
+ */
+struct drm_suballoc {
+	struct list_head olist;
+	struct list_head flist;
+	struct drm_suballoc_manager *manager;
+	size_t soffset;
+	size_t eoffset;
+	struct dma_fence *fence;
+};
+
+void drm_suballoc_manager_init(struct drm_suballoc_manager *sa_manager,
+			       size_t size, size_t align);
+
+void drm_suballoc_manager_fini(struct drm_suballoc_manager *sa_manager);
+
+struct drm_suballoc *
+drm_suballoc_new(struct drm_suballoc_manager *sa_manager, size_t size,
+		 gfp_t gfp, bool intr, size_t align);
+
+void drm_suballoc_free(struct drm_suballoc *sa, struct dma_fence *fence);
+
+/**
+ * drm_suballoc_soffset - Range start.
+ * @sa: The struct drm_suballoc.
+ *
+ * Return: The start of the allocated range.
+ */
+static inline size_t drm_suballoc_soffset(struct drm_suballoc *sa)
+{
+	return sa->soffset;
+}
+
+/**
+ * drm_suballoc_eoffset - Range end.
+ * @sa: The struct drm_suballoc.
+ *
+ * Return: The end of the allocated range + 1.
+ */
+static inline size_t drm_suballoc_eoffset(struct drm_suballoc *sa)
+{
+	return sa->eoffset;
+}
+
+/**
+ * drm_suballoc_size - Range size.
+ * @sa: The struct drm_suballoc.
+ *
+ * Return: The size of the allocated range.
+ */
+static inline size_t drm_suballoc_size(struct drm_suballoc *sa)
+{
+	return sa->eoffset - sa->soffset;
+}
+
+#ifdef CONFIG_DEBUG_FS
+void drm_suballoc_dump_debug_info(struct drm_suballoc_manager *sa_manager,
+				  struct drm_printer *p,
+				  unsigned long long suballoc_base);
+#else
+static inline void
+drm_suballoc_dump_debug_info(struct drm_suballoc_manager *sa_manager,
+			     struct drm_printer *p,
+			     unsigned long long suballoc_base)
+{ }
+
+#endif
+
+#endif /* _DRM_SUBALLOC_H_ */