/* SPDX-License-Identifier: GPL-2.0 OR MIT */
/**************************************************************************
 *
 * Copyright (c) 2006-2009 VMware, Inc., Palo Alto, CA., USA
 * All Rights Reserved.
 *
 * 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, sub license, 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 (including the
 * next paragraph) 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 NON-INFRINGEMENT. IN NO EVENT SHALL
 * THE COPYRIGHT HOLDERS, AUTHORS AND/OR ITS SUPPLIERS 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.
 *
 **************************************************************************/
/*
 * Authors: Thomas Hellstrom <thellstrom-at-vmware-dot-com>
 */

#define pr_fmt(fmt) "[TTM] " fmt

#include <linux/export.h>

#include <drm/ttm/ttm_bo.h>
#include <drm/ttm/ttm_placement.h>
#include <drm/ttm/ttm_tt.h>

#include <drm/drm_drv.h>
#include <drm/drm_managed.h>

#ifdef __linux__

static vm_fault_t ttm_bo_vm_fault_idle(struct ttm_buffer_object *bo,
                                struct vm_fault *vmf)
{
        long err = 0;

        /*
         * Quick non-stalling check for idle.
         */
        if (dma_resv_test_signaled(bo->base.resv, DMA_RESV_USAGE_KERNEL))
                return 0;

        /*
         * If possible, avoid waiting for GPU with mmap_lock
         * held.  We only do this if the fault allows retry and this
         * is the first attempt.
         */
        if (fault_flag_allow_retry_first(vmf->flags)) {
                if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
                        return VM_FAULT_RETRY;

                drm_gem_object_get(&bo->base);
                mmap_read_unlock(vmf->vma->vm_mm);
                (void)dma_resv_wait_timeout(bo->base.resv,
                                            DMA_RESV_USAGE_KERNEL, true,
                                            MAX_SCHEDULE_TIMEOUT);
                dma_resv_unlock(bo->base.resv);
                drm_gem_object_put(&bo->base);
                return VM_FAULT_RETRY;
        }

        /*
         * Ordinary wait.
         */
        err = dma_resv_wait_timeout(bo->base.resv, DMA_RESV_USAGE_KERNEL, true,
                                    MAX_SCHEDULE_TIMEOUT);
        if (unlikely(err < 0)) {
                return (err != -ERESTARTSYS) ? VM_FAULT_SIGBUS :
                        VM_FAULT_NOPAGE;
        }

        return 0;
}

static unsigned long ttm_bo_io_mem_pfn(struct ttm_buffer_object *bo,
                                       unsigned long page_offset)
{
        struct ttm_device *bdev = bo->bdev;

        if (bdev->funcs->io_mem_pfn)
                return bdev->funcs->io_mem_pfn(bo, page_offset);

        return (bo->resource->bus.offset >> PAGE_SHIFT) + page_offset;
}

/**
 * ttm_bo_vm_reserve - Reserve a buffer object in a retryable vm callback
 * @bo: The buffer object
 * @vmf: The fault structure handed to the callback
 *
 * vm callbacks like fault() and *_mkwrite() allow for the mmap_lock to be dropped
 * during long waits, and after the wait the callback will be restarted. This
 * is to allow other threads using the same virtual memory space concurrent
 * access to map(), unmap() completely unrelated buffer objects. TTM buffer
 * object reservations sometimes wait for GPU and should therefore be
 * considered long waits. This function reserves the buffer object interruptibly
 * taking this into account. Starvation is avoided by the vm system not
 * allowing too many repeated restarts.
 * This function is intended to be used in customized fault() and _mkwrite()
 * handlers.
 *
 * Return:
 *    0 on success and the bo was reserved.
 *    VM_FAULT_RETRY if blocking wait.
 *    VM_FAULT_NOPAGE if blocking wait and retrying was not allowed.
 */
vm_fault_t ttm_bo_vm_reserve(struct ttm_buffer_object *bo,
                             struct vm_fault *vmf)
{
        /*
         * Work around locking order reversal in fault / nopfn
         * between mmap_lock and bo_reserve: Perform a trylock operation
         * for reserve, and if it fails, retry the fault after waiting
         * for the buffer to become unreserved.
         */
        if (unlikely(!dma_resv_trylock(bo->base.resv))) {
                /*
                 * If the fault allows retry and this is the first
                 * fault attempt, we try to release the mmap_lock
                 * before waiting
                 */
                if (fault_flag_allow_retry_first(vmf->flags)) {
                        if (!(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) {
                                drm_gem_object_get(&bo->base);
                                mmap_read_unlock(vmf->vma->vm_mm);
                                if (!dma_resv_lock_interruptible(bo->base.resv,
                                                                 NULL))
                                        dma_resv_unlock(bo->base.resv);
                                drm_gem_object_put(&bo->base);
                        }

                        return VM_FAULT_RETRY;
                }

                if (dma_resv_lock_interruptible(bo->base.resv, NULL))
                        return VM_FAULT_NOPAGE;
        }

        /*
         * Refuse to fault imported pages. This should be handled
         * (if at all) by redirecting mmap to the exporter.
         */
        if (bo->ttm && (bo->ttm->page_flags & TTM_TT_FLAG_EXTERNAL)) {
                if (!(bo->ttm->page_flags & TTM_TT_FLAG_EXTERNAL_MAPPABLE)) {
                        dma_resv_unlock(bo->base.resv);
                        return VM_FAULT_SIGBUS;
                }
        }

        return 0;
}
EXPORT_SYMBOL(ttm_bo_vm_reserve);

/**
 * ttm_bo_vm_fault_reserved - TTM fault helper
 * @vmf: The struct vm_fault given as argument to the fault callback
 * @prot: The page protection to be used for this memory area.
 * @num_prefault: Maximum number of prefault pages. The caller may want to
 * specify this based on madvice settings and the size of the GPU object
 * backed by the memory.
 *
 * This function inserts one or more page table entries pointing to the
 * memory backing the buffer object, and then returns a return code
 * instructing the caller to retry the page access.
 *
 * Return:
 *   VM_FAULT_NOPAGE on success or pending signal
 *   VM_FAULT_SIGBUS on unspecified error
 *   VM_FAULT_OOM on out-of-memory
 *   VM_FAULT_RETRY if retryable wait
 */
vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
                                    pgprot_t prot,
                                    pgoff_t num_prefault)
{
        struct vm_area_struct *vma = vmf->vma;
        struct ttm_buffer_object *bo = vma->vm_private_data;
        struct ttm_device *bdev = bo->bdev;
        unsigned long page_offset;
        unsigned long page_last;
        unsigned long pfn;
        struct ttm_tt *ttm = NULL;
        struct vm_page *page;
        int err;
        pgoff_t i;
        vm_fault_t ret = VM_FAULT_NOPAGE;
        unsigned long address = vmf->address;

        /*
         * Wait for buffer data in transit, due to a pipelined
         * move.
         */
        ret = ttm_bo_vm_fault_idle(bo, vmf);
        if (unlikely(ret != 0))
                return ret;

        err = ttm_mem_io_reserve(bdev, bo->resource);
        if (unlikely(err != 0))
                return VM_FAULT_SIGBUS;

        page_offset = ((address - vma->vm_start) >> PAGE_SHIFT) +
                vma->vm_pgoff - drm_vma_node_start(&bo->base.vma_node);
        page_last = vma_pages(vma) + vma->vm_pgoff -
                drm_vma_node_start(&bo->base.vma_node);

        if (unlikely(page_offset >= PFN_UP(bo->base.size)))
                return VM_FAULT_SIGBUS;

        prot = ttm_io_prot(bo, bo->resource, prot);
        if (!bo->resource->bus.is_iomem) {
                struct ttm_operation_ctx ctx = {
                        .interruptible = true,
                        .no_wait_gpu = false,
                };

                ttm = bo->ttm;
                err = ttm_bo_populate(bo, &ctx);
                if (err) {
                        if (err == -EINTR || err == -ERESTARTSYS ||
                            err == -EAGAIN)
                                return VM_FAULT_NOPAGE;

                        pr_debug("TTM fault hit %pe.\n", ERR_PTR(err));
                        return VM_FAULT_SIGBUS;
                }
        } else {
                /* Iomem should not be marked encrypted */
                prot = pgprot_decrypted(prot);
        }

        /*
         * Speculatively prefault a number of pages. Only error on
         * first page.
         */
        for (i = 0; i < num_prefault; ++i) {
                if (bo->resource->bus.is_iomem) {
                        pfn = ttm_bo_io_mem_pfn(bo, page_offset);
                } else {
                        page = ttm->pages[page_offset];
                        if (unlikely(!page && i == 0)) {
                                return VM_FAULT_OOM;
                        } else if (unlikely(!page)) {
                                break;
                        }
                        pfn = page_to_pfn(page);
                }

                /*
                 * Note that the value of @prot at this point may differ from
                 * the value of @vma->vm_page_prot in the caching- and
                 * encryption bits. This is because the exact location of the
                 * data may not be known at mmap() time and may also change
                 * at arbitrary times while the data is mmap'ed.
                 * See vmf_insert_pfn_prot() for a discussion.
                 */
                ret = vmf_insert_pfn_prot(vma, address, pfn, prot);

                /* Never error on prefaulted PTEs */
                if (unlikely((ret & VM_FAULT_ERROR))) {
                        if (i == 0)
                                return VM_FAULT_NOPAGE;
                        else
                                break;
                }

                address += PAGE_SIZE;
                if (unlikely(++page_offset >= page_last))
                        break;
        }
        return ret;
}
EXPORT_SYMBOL(ttm_bo_vm_fault_reserved);

static void ttm_bo_release_dummy_page(struct drm_device *dev, void *res)
{
        struct page *dummy_page = (struct page *)res;

        __free_page(dummy_page);
}

vm_fault_t ttm_bo_vm_dummy_page(struct vm_fault *vmf, pgprot_t prot)
{
        struct vm_area_struct *vma = vmf->vma;
        struct ttm_buffer_object *bo = vma->vm_private_data;
        struct drm_device *ddev = bo->base.dev;
        vm_fault_t ret = VM_FAULT_NOPAGE;
        unsigned long address;
        unsigned long pfn;
        struct page *page;

        /* Allocate new dummy page to map all the VA range in this VMA to it*/
        page = alloc_page(GFP_KERNEL | __GFP_ZERO);
        if (!page)
                return VM_FAULT_OOM;

        /* Set the page to be freed using drmm release action */
        if (drmm_add_action_or_reset(ddev, ttm_bo_release_dummy_page, page))
                return VM_FAULT_OOM;

        pfn = page_to_pfn(page);

        /* Prefault the entire VMA range right away to avoid further faults */
        for (address = vma->vm_start; address < vma->vm_end;
             address += PAGE_SIZE)
                ret = vmf_insert_pfn_prot(vma, address, pfn, prot);

        return ret;
}
EXPORT_SYMBOL(ttm_bo_vm_dummy_page);

vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
{
        struct vm_area_struct *vma = vmf->vma;
        pgprot_t prot;
        struct ttm_buffer_object *bo = vma->vm_private_data;
        struct drm_device *ddev = bo->base.dev;
        vm_fault_t ret;
        int idx;

        ret = ttm_bo_vm_reserve(bo, vmf);
        if (ret)
                return ret;

        prot = vma->vm_page_prot;
        if (drm_dev_enter(ddev, &idx)) {
                ret = ttm_bo_vm_fault_reserved(vmf, prot, TTM_BO_VM_NUM_PREFAULT);
                drm_dev_exit(idx);
        } else {
                ret = ttm_bo_vm_dummy_page(vmf, prot);
        }
        if (ret == VM_FAULT_RETRY && !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT))
                return ret;

        dma_resv_unlock(bo->base.resv);

        return ret;
}
EXPORT_SYMBOL(ttm_bo_vm_fault);

#else /* !__linux__ */

static vm_fault_t ttm_bo_vm_fault_idle(struct ttm_buffer_object *bo,
    struct uvm_faultinfo *ufi)
{
        long err = 0;

        /*
         * Quick non-stalling check for idle.
         */
        if (dma_resv_test_signaled(bo->base.resv, DMA_RESV_USAGE_KERNEL))
                return 0;

#ifdef __linux__
        /*
         * If possible, avoid waiting for GPU with mmap_lock
         * held.  We only do this if the fault allows retry and this
         * is the first attempt.
         */
        if (fault_flag_allow_retry_first(vmf->flags)) {
                if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
                        return VM_FAULT_RETRY;

                ttm_bo_get(bo);
                mmap_read_unlock(vmf->vma->vm_mm);
                (void) dma_fence_wait(bo->moving, true);
                (void)dma_resv_wait_timeout(bo->base.resv,
                                            DMA_RESV_USAGE_KERNEL, true,
                                            MAX_SCHEDULE_TIMEOUT);
                dma_resv_unlock(bo->base.resv);
                ttm_bo_put(bo);
                return VM_FAULT_RETRY;
        }
#endif

        /*
         * Ordinary wait.
         */
        err = dma_resv_wait_timeout(bo->base.resv, DMA_RESV_USAGE_KERNEL, true,
                                    MAX_SCHEDULE_TIMEOUT);
        if (unlikely(err < 0)) {
                return (err != -ERESTARTSYS) ? VM_FAULT_SIGBUS :
                        VM_FAULT_NOPAGE;
        }

        return 0;
}

static unsigned long ttm_bo_io_mem_pfn(struct ttm_buffer_object *bo,
                                       unsigned long page_offset)
{
        struct ttm_device *bdev = bo->bdev;

        if (bdev->funcs->io_mem_pfn)
                return bdev->funcs->io_mem_pfn(bo, page_offset);

        return (bo->resource->bus.offset >> PAGE_SHIFT) + page_offset;
}

/**
 * ttm_bo_vm_reserve - Reserve a buffer object in a retryable vm callback
 * @bo: The buffer object
 * @vmf: The fault structure handed to the callback
 *
 * vm callbacks like fault() and *_mkwrite() allow for the mmap_lock to be dropped
 * during long waits, and after the wait the callback will be restarted. This
 * is to allow other threads using the same virtual memory space concurrent
 * access to map(), unmap() completely unrelated buffer objects. TTM buffer
 * object reservations sometimes wait for GPU and should therefore be
 * considered long waits. This function reserves the buffer object interruptibly
 * taking this into account. Starvation is avoided by the vm system not
 * allowing too many repeated restarts.
 * This function is intended to be used in customized fault() and _mkwrite()
 * handlers.
 *
 * Return:
 *    0 on success and the bo was reserved.
 *    VM_FAULT_RETRY if blocking wait.
 *    VM_FAULT_NOPAGE if blocking wait and retrying was not allowed.
 */
vm_fault_t ttm_bo_vm_reserve(struct ttm_buffer_object *bo)
{
        /*
         * Work around locking order reversal in fault / nopfn
         * between mmap_lock and bo_reserve: Perform a trylock operation
         * for reserve, and if it fails, retry the fault after waiting
         * for the buffer to become unreserved.
         */
        if (unlikely(!dma_resv_trylock(bo->base.resv))) {
#ifdef __linux__
                /*
                 * If the fault allows retry and this is the first
                 * fault attempt, we try to release the mmap_lock
                 * before waiting
                 */
                if (fault_flag_allow_retry_first(vmf->flags)) {
                        if (!(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) {
                                ttm_bo_get(bo);
                                mmap_read_unlock(vmf->vma->vm_mm);
                                if (!dma_resv_lock_interruptible(bo->base.resv,
                                                                 NULL))
                                        dma_resv_unlock(bo->base.resv);
                                ttm_bo_put(bo);
                        }

                        return VM_FAULT_RETRY;
                }
#endif

                if (dma_resv_lock_interruptible(bo->base.resv, NULL))
                        return VM_FAULT_NOPAGE;
        }

        /*
         * Refuse to fault imported pages. This should be handled
         * (if at all) by redirecting mmap to the exporter.
         */
        if (bo->ttm && (bo->ttm->page_flags & TTM_TT_FLAG_EXTERNAL)) {
                if (!(bo->ttm->page_flags & TTM_TT_FLAG_EXTERNAL_MAPPABLE)) {
                        dma_resv_unlock(bo->base.resv);
                        return VM_FAULT_SIGBUS;
                }
        }

        return 0;
}

vm_fault_t ttm_bo_vm_fault_reserved(struct uvm_faultinfo *ufi,
                                    vaddr_t vaddr,
                                    pgoff_t num_prefault,
                                    pgoff_t fault_page_size)
{
        struct uvm_object *uobj = ufi->entry->object.uvm_obj;
        struct ttm_buffer_object *bo = (struct ttm_buffer_object *)uobj;
        struct ttm_device *bdev = bo->bdev;
        unsigned long page_offset;
        unsigned long page_last;
        unsigned long pfn;
        struct ttm_tt *ttm = NULL;
        struct vm_page *page;
        bus_addr_t addr;
        paddr_t paddr;
        vm_prot_t prot;
        int pmap_flags;
        int err;
        pgoff_t i;
        vm_fault_t ret = VM_FAULT_NOPAGE;
        unsigned long address = (unsigned long)vaddr;

        /*
         * Wait for buffer data in transit, due to a pipelined
         * move.
         */
        ret = ttm_bo_vm_fault_idle(bo, ufi);
        if (unlikely(ret != 0))
                return ret;
        ret = VM_FAULT_NOPAGE;

        err = ttm_mem_io_reserve(bdev, bo->resource);
        if (unlikely(err != 0))
                return VM_FAULT_SIGBUS;

        page_offset = ((address - ufi->entry->start) >> PAGE_SHIFT) +
            drm_vma_node_start(&bo->base.vma_node) - (ufi->entry->offset >> PAGE_SHIFT);
        page_last = ((ufi->entry->end - ufi->entry->start) >> PAGE_SHIFT) +
            drm_vma_node_start(&bo->base.vma_node) - (ufi->entry->offset >> PAGE_SHIFT);

        if (unlikely(page_offset >= PFN_UP(bo->base.size)))
                return VM_FAULT_SIGBUS;

        prot = ufi->entry->protection;
        pmap_flags = ttm_io_prot(bo, bo->resource, 0);
        if (!bo->resource->bus.is_iomem) {
                struct ttm_operation_ctx ctx = {
                        .interruptible = true,
                        .no_wait_gpu = false,
                };

                ttm = bo->ttm;
                err = ttm_bo_populate(bo, &ctx);
                if (err) {
                        if (err == -EINTR || err == -ERESTARTSYS ||
                            err == -EAGAIN)
                                return VM_FAULT_NOPAGE;

                        pr_debug("TTM fault hit %pe.\n", ERR_PTR(err));
                        return VM_FAULT_SIGBUS;
                }
        }

#ifdef __linux__
        /* We don't prefault on huge faults. Yet. */
        if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) && fault_page_size != 1)
                return ttm_bo_vm_insert_huge(vmf, bo, page_offset,
                                             fault_page_size, prot);
#endif

        /*
         * Speculatively prefault a number of pages. Only error on
         * first page.
         */
        for (i = 0; i < num_prefault; ++i) {
                if (bo->resource->bus.is_iomem) {
                        pfn = ttm_bo_io_mem_pfn(bo, page_offset);
                        addr = pfn << PAGE_SHIFT;
                        paddr = bus_space_mmap(bdev->memt, addr, 0, prot, 0);
                } else {
                        page = ttm->pages[page_offset];
                        if (unlikely(!page && i == 0)) {
                                return VM_FAULT_OOM;
                        } else if (unlikely(!page)) {
                                break;
                        }
                        paddr = VM_PAGE_TO_PHYS(page);
                }

                err = pmap_enter(ufi->orig_map->pmap, address,
                    paddr | pmap_flags, prot, PMAP_CANFAIL | prot);

                /* Never error on prefaulted PTEs */
                if (unlikely(err)) {
                        ret = VM_FAULT_OOM;
                        if (i == 0)
                                return VM_FAULT_NOPAGE;
                        else
                                break;
                }

                address += PAGE_SIZE;
                if (unlikely(++page_offset >= page_last))
                        break;
        }
        pmap_update(ufi->orig_map->pmap);
        return ret;
}
EXPORT_SYMBOL(ttm_bo_vm_fault_reserved);

int
ttm_bo_vm_fault(struct uvm_faultinfo *ufi, vaddr_t vaddr, vm_page_t *pps,
    int npages, int centeridx, vm_fault_t fault_type,
    vm_prot_t access_type, int flags)
{
        struct uvm_object *uobj = ufi->entry->object.uvm_obj;
        struct ttm_buffer_object *bo = (struct ttm_buffer_object *)uobj;
        vm_fault_t ret;

        ret = ttm_bo_vm_reserve(bo);
        if (ret) {
                goto out;
        }

        ret = ttm_bo_vm_fault_reserved(ufi, vaddr, TTM_BO_VM_NUM_PREFAULT, 1);
        dma_resv_unlock(bo->base.resv);
out:
        switch (ret) {
        case VM_FAULT_NOPAGE:
                ret = 0;
                break;
        case VM_FAULT_RETRY:
                ret = ERESTART;
                break;
        default:
                ret = EACCES;
                break;
        }
        uvmfault_unlockall(ufi, NULL, uobj);
        return ret;
}
EXPORT_SYMBOL(ttm_bo_vm_fault);

#endif /* !__linux__ */

#ifdef notyet
void ttm_bo_vm_open(struct vm_area_struct *vma)
{
        struct ttm_buffer_object *bo = vma->vm_private_data;

        WARN_ON(bo->bdev->dev_mapping != vma->vm_file->f_mapping);

        drm_gem_object_get(&bo->base);
}
EXPORT_SYMBOL(ttm_bo_vm_open);

void ttm_bo_vm_close(struct vm_area_struct *vma)
{
        struct ttm_buffer_object *bo = vma->vm_private_data;

        drm_gem_object_put(&bo->base);
        vma->vm_private_data = NULL;
}
EXPORT_SYMBOL(ttm_bo_vm_close);

static int ttm_bo_vm_access_kmap(struct ttm_buffer_object *bo,
                                 unsigned long offset,
                                 uint8_t *buf, int len, int write)
{
        unsigned long page = offset >> PAGE_SHIFT;
        unsigned long bytes_left = len;
        int ret;

        /* Copy a page at a time, that way no extra virtual address
         * mapping is needed
         */
        offset -= page << PAGE_SHIFT;
        do {
                unsigned long bytes = min(bytes_left, PAGE_SIZE - offset);
                struct ttm_bo_kmap_obj map;
                void *ptr;
                bool is_iomem;

                ret = ttm_bo_kmap(bo, page, 1, &map);
                if (ret)
                        return ret;

                ptr = (uint8_t *)ttm_kmap_obj_virtual(&map, &is_iomem) + offset;
                WARN_ON_ONCE(is_iomem);
                if (write)
                        memcpy(ptr, buf, bytes);
                else
                        memcpy(buf, ptr, bytes);
                ttm_bo_kunmap(&map);

                page++;
                buf += bytes;
                bytes_left -= bytes;
                offset = 0;
        } while (bytes_left);

        return len;
}

/**
 * ttm_bo_access - Helper to access a buffer object
 *
 * @bo: ttm buffer object
 * @offset: access offset into buffer object
 * @buf: pointer to caller memory to read into or write from
 * @len: length of access
 * @write: write access
 *
 * Utility function to access a buffer object. Useful when buffer object cannot
 * be easily mapped (non-contiguous, non-visible, etc...). Should not directly
 * be exported to user space via a peak / poke interface.
 *
 * Returns:
 * @len if successful, negative error code on failure.
 */
int ttm_bo_access(struct ttm_buffer_object *bo, unsigned long offset,
                  void *buf, int len, int write)
{
        int ret;

        if (len < 1 || (offset + len) > bo->base.size)
                return -EIO;

        ret = ttm_bo_reserve(bo, true, false, NULL);
        if (ret)
                return ret;

        if (!bo->resource) {
                ret = -ENODATA;
                goto unlock;
        }

        switch (bo->resource->mem_type) {
        case TTM_PL_SYSTEM:
                fallthrough;
        case TTM_PL_TT:
                ret = ttm_bo_vm_access_kmap(bo, offset, buf, len, write);
                break;
        default:
                if (bo->bdev->funcs->access_memory)
                        ret = bo->bdev->funcs->access_memory
                                (bo, offset, buf, len, write);
                else
                        ret = -EIO;
        }

unlock:
        ttm_bo_unreserve(bo);

        return ret;
}
EXPORT_SYMBOL(ttm_bo_access);

int ttm_bo_vm_access(struct vm_area_struct *vma, unsigned long addr,
                     void *buf, int len, int write)
{
        struct ttm_buffer_object *bo = vma->vm_private_data;
        unsigned long offset = (addr) - vma->vm_start +
                ((vma->vm_pgoff - drm_vma_node_start(&bo->base.vma_node))
                 << PAGE_SHIFT);

        return ttm_bo_access(bo, offset, buf, len, write);
}
EXPORT_SYMBOL(ttm_bo_vm_access);

static const struct vm_operations_struct ttm_bo_vm_ops = {
        .fault = ttm_bo_vm_fault,
        .open = ttm_bo_vm_open,
        .close = ttm_bo_vm_close,
        .access = ttm_bo_vm_access,
};
#endif

void
ttm_bo_vm_reference(struct uvm_object *uobj)
{
        struct ttm_buffer_object *bo =
            (struct ttm_buffer_object *)uobj;

        drm_gem_object_get(&bo->base);
}

void
ttm_bo_vm_detach(struct uvm_object *uobj)
{
        struct ttm_buffer_object *bo = (struct ttm_buffer_object *)uobj;

        drm_gem_object_put(&bo->base);
}

const struct uvm_pagerops ttm_bo_vm_ops = {
        .pgo_fault = ttm_bo_vm_fault,
        .pgo_reference = ttm_bo_vm_reference,
        .pgo_detach = ttm_bo_vm_detach
};

#ifdef __linux__
/**
 * ttm_bo_mmap_obj - mmap memory backed by a ttm buffer object.
 *
 * @vma:       vma as input from the fbdev mmap method.
 * @bo:        The bo backing the address space.
 *
 * Maps a buffer object.
 */
int ttm_bo_mmap_obj(struct vm_area_struct *vma, struct ttm_buffer_object *bo)
{
        /* Enforce no COW since would have really strange behavior with it. */
        if (is_cow_mapping(vma->vm_flags))
                return -EINVAL;

        drm_gem_object_get(&bo->base);

        /*
         * Drivers may want to override the vm_ops field. Otherwise we
         * use TTM's default callbacks.
         */
        if (!vma->vm_ops)
                vma->vm_ops = &ttm_bo_vm_ops;

        /*
         * Note: We're transferring the bo reference to
         * vma->vm_private_data here.
         */

        vma->vm_private_data = bo;

        vm_flags_set(vma, VM_PFNMAP | VM_IO | VM_DONTEXPAND | VM_DONTDUMP);
        return 0;
}
EXPORT_SYMBOL(ttm_bo_mmap_obj);
#else /* !__linux__ */
int ttm_bo_mmap_obj(struct ttm_buffer_object *bo)
{
        /* Enforce no COW since would have really strange behavior with it. */
#ifdef notyet
        if (UVM_ET_ISCOPYONWRITE(entry))
                return -EINVAL;
#endif

        drm_gem_object_get(&bo->base);

        /*
         * Drivers may want to override the vm_ops field. Otherwise we
         * use TTM's default callbacks.
         */
        if (bo->base.uobj.pgops == NULL)
                uvm_obj_init(&bo->base.uobj, &ttm_bo_vm_ops, 1);

        /*
         * Note: We're transferring the bo reference to
         * vma->vm_private_data here.
         */

#ifdef notyet
        vma->vm_private_data = bo;

        vma->vm_flags |= VM_PFNMAP;
        vma->vm_flags |= VM_IO | VM_DONTEXPAND | VM_DONTDUMP;
#endif
        return 0;
}
#endif /* !__linux__ */