Re: [Intel-gfx] [PATCH v3 06/12] drm/ttm: Add a generic TTM memcpy move for page-based iomem

[Matthew Auld <matthew.william.auld@gmail.com>]

On Tue, 25 May 2021 at 10:32, Thomas Hellström
<thomas.hellstrom@linux.intel.com> wrote:
>
>
> On 5/25/21 11:18 AM, Matthew Auld wrote:
> > On Fri, 21 May 2021 at 16:33, Thomas Hellström
> > <thomas.hellstrom@linux.intel.com> wrote:
> >> The internal ttm_bo_util memcpy uses ioremap functionality, and while it
> >> probably might be possible to use it for copying in- and out of
> >> sglist represented io memory, using io_mem_reserve() / io_mem_free()
> >> callbacks, that would cause problems with fault().
> >> Instead, implement a method mapping page-by-page using kmap_local()
> >> semantics. As an additional benefit we then avoid the occasional global
> >> TLB flushes of ioremap() and consuming ioremap space, elimination of a
> >> critical point of failure and with a slight change of semantics we could
> >> also push the memcpy out async for testing and async driver development
> >> purposes.
> >>
> >> A special linear iomem iterator is introduced internally to mimic the
> >> old ioremap behaviour for code-paths that can't immediately be ported
> >> over. This adds to the code size and should be considered a temporary
> >> solution.
> >>
> >> Looking at the code we have a lot of checks for iomap tagged pointers.
> >> Ideally we should extend the core memremap functions to also accept
> >> uncached memory and kmap_local functionality. Then we could strip a
> >> lot of code.
> >>
> >> Cc: Christian König <christian.koenig@amd.com>
> >> Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> >> ---
> >> v3:
> >> - Split up in various TTM files and addressed review comments by
> >>    Christian König. Tested and fixed legacy iomap memcpy path on i915.
> >> ---
> >>   drivers/gpu/drm/ttm/ttm_bo_util.c  | 278 ++++++++++-------------------
> >>   drivers/gpu/drm/ttm/ttm_module.c   |  35 ++++
> >>   drivers/gpu/drm/ttm/ttm_resource.c | 166 +++++++++++++++++
> >>   drivers/gpu/drm/ttm/ttm_tt.c       |  42 +++++
> >>   include/drm/ttm/ttm_bo_driver.h    |  28 +++
> >>   include/drm/ttm/ttm_caching.h      |   2 +
> >>   include/drm/ttm/ttm_kmap_iter.h    |  61 +++++++
> >>   include/drm/ttm/ttm_resource.h     |  61 +++++++
> >>   include/drm/ttm/ttm_tt.h           |  16 ++
> >>   9 files changed, 508 insertions(+), 181 deletions(-)
> >>   create mode 100644 include/drm/ttm/ttm_kmap_iter.h
> >>
> >> diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
> >> index ae8b61460724..912cbe8e60a2 100644
> >> --- a/drivers/gpu/drm/ttm/ttm_bo_util.c
> >> +++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
> >> @@ -72,190 +72,126 @@ void ttm_mem_io_free(struct ttm_device *bdev,
> >>          mem->bus.addr = NULL;
> >>   }
> >>
> >> -static int ttm_resource_ioremap(struct ttm_device *bdev,
> >> -                              struct ttm_resource *mem,
> >> -                              void **virtual)
> >> +/**
> >> + * ttm_move_memcpy - Helper to perform a memcpy ttm move operation.
> >> + * @bo: The struct ttm_buffer_object.
> >> + * @new_mem: The struct ttm_resource we're moving to (copy destination).
> >> + * @new_iter: A struct ttm_kmap_iter representing the destination resource.
> >> + * @src_iter: A struct ttm_kmap_iter representing the source resource.
> >> + *
> >> + * This function is intended to be able to move out async under a
> >> + * dma-fence if desired.
> >> + */
> >> +void ttm_move_memcpy(struct ttm_buffer_object *bo,
> >> +                    struct ttm_resource *dst_mem,
> >> +                    struct ttm_kmap_iter *dst_iter,
> >> +                    struct ttm_kmap_iter *src_iter)
> >>   {
> >> -       int ret;
> >> -       void *addr;
> >> -
> >> -       *virtual = NULL;
> >> -       ret = ttm_mem_io_reserve(bdev, mem);
> >> -       if (ret || !mem->bus.is_iomem)
> >> -               return ret;
> >> +       const struct ttm_kmap_iter_ops *dst_ops = dst_iter->ops;
> >> +       const struct ttm_kmap_iter_ops *src_ops = src_iter->ops;
> >> +       struct ttm_tt *ttm = bo->ttm;
> >> +       struct dma_buf_map src_map, dst_map;
> >> +       pgoff_t i;
> >>
> >> -       if (mem->bus.addr) {
> >> -               addr = mem->bus.addr;
> >> -       } else {
> >> -               size_t bus_size = (size_t)mem->num_pages << PAGE_SHIFT;
> >> +       /* Single TTM move. NOP */
> >> +       if (dst_ops->maps_tt && src_ops->maps_tt)
> >> +               return;
> >>
> >> -               if (mem->bus.caching == ttm_write_combined)
> >> -                       addr = ioremap_wc(mem->bus.offset, bus_size);
> >> -#ifdef CONFIG_X86
> >> -               else if (mem->bus.caching == ttm_cached)
> >> -                       addr = ioremap_cache(mem->bus.offset, bus_size);
> >> -#endif
> >> -               else
> >> -                       addr = ioremap(mem->bus.offset, bus_size);
> >> -               if (!addr) {
> >> -                       ttm_mem_io_free(bdev, mem);
> >> -                       return -ENOMEM;
> >> +       /* Don't move nonexistent data. Clear destination instead. */
> >> +       if (src_ops->maps_tt && (!ttm || !ttm_tt_is_populated(ttm))) {
> >> +               if (ttm && !(ttm->page_flags & TTM_PAGE_FLAG_ZERO_ALLOC))
> >> +                       return;
> >> +
> >> +               for (i = 0; i < dst_mem->num_pages; ++i) {
> >> +                       dst_ops->map_local(dst_iter, &dst_map, i);
> >> +                       if (dst_map.is_iomem)
> >> +                               memset_io(dst_map.vaddr_iomem, 0, PAGE_SIZE);
> >> +                       else
> >> +                               memset(dst_map.vaddr, 0, PAGE_SIZE);
> >> +                       if (dst_ops->unmap_local)
> >> +                               dst_ops->unmap_local(dst_iter, &dst_map);
> >>                  }
> >> +               return;
> >>          }
> >> -       *virtual = addr;
> >> -       return 0;
> >> -}
> >> -
> >> -static void ttm_resource_iounmap(struct ttm_device *bdev,
> >> -                               struct ttm_resource *mem,
> >> -                               void *virtual)
> >> -{
> >> -       if (virtual && mem->bus.addr == NULL)
> >> -               iounmap(virtual);
> >> -       ttm_mem_io_free(bdev, mem);
> >> -}
> >> -
> >> -static int ttm_copy_io_page(void *dst, void *src, unsigned long page)
> >> -{
> >> -       uint32_t *dstP =
> >> -           (uint32_t *) ((unsigned long)dst + (page << PAGE_SHIFT));
> >> -       uint32_t *srcP =
> >> -           (uint32_t *) ((unsigned long)src + (page << PAGE_SHIFT));
> >> -
> >> -       int i;
> >> -       for (i = 0; i < PAGE_SIZE / sizeof(uint32_t); ++i)
> >> -               iowrite32(ioread32(srcP++), dstP++);
> >> -       return 0;
> >> -}
> >> -
> >> -static int ttm_copy_io_ttm_page(struct ttm_tt *ttm, void *src,
> >> -                               unsigned long page,
> >> -                               pgprot_t prot)
> >> -{
> >> -       struct page *d = ttm->pages[page];
> >> -       void *dst;
> >> -
> >> -       if (!d)
> >> -               return -ENOMEM;
> >> -
> >> -       src = (void *)((unsigned long)src + (page << PAGE_SHIFT));
> >> -       dst = kmap_atomic_prot(d, prot);
> >> -       if (!dst)
> >> -               return -ENOMEM;
> >> -
> >> -       memcpy_fromio(dst, src, PAGE_SIZE);
> >> -
> >> -       kunmap_atomic(dst);
> >> -
> >> -       return 0;
> >> -}
> >> -
> >> -static int ttm_copy_ttm_io_page(struct ttm_tt *ttm, void *dst,
> >> -                               unsigned long page,
> >> -                               pgprot_t prot)
> >> -{
> >> -       struct page *s = ttm->pages[page];
> >> -       void *src;
> >> -
> >> -       if (!s)
> >> -               return -ENOMEM;
> >> -
> >> -       dst = (void *)((unsigned long)dst + (page << PAGE_SHIFT));
> >> -       src = kmap_atomic_prot(s, prot);
> >> -       if (!src)
> >> -               return -ENOMEM;
> >>
> >> -       memcpy_toio(dst, src, PAGE_SIZE);
> >> -
> >> -       kunmap_atomic(src);
> >> +       for (i = 0; i < dst_mem->num_pages; ++i) {
> >> +               dst_ops->map_local(dst_iter, &dst_map, i);
> >> +               src_ops->map_local(src_iter, &src_map, i);
> >> +
> >> +               if (!src_map.is_iomem && !dst_map.is_iomem) {
> >> +                       memcpy(dst_map.vaddr, src_map.vaddr, PAGE_SIZE);
> >> +               } else if (!src_map.is_iomem) {
> >> +                       dma_buf_map_memcpy_to(&dst_map, src_map.vaddr,
> >> +                                             PAGE_SIZE);
> >> +               } else if (!dst_map.is_iomem) {
> >> +                       memcpy_fromio(dst_map.vaddr, src_map.vaddr_iomem,
> >> +                                     PAGE_SIZE);
> >> +               } else {
> >> +                       int j;
> >> +                       u32 __iomem *src = src_map.vaddr_iomem;
> >> +                       u32 __iomem *dst = dst_map.vaddr_iomem;
> >>
> >> -       return 0;
> >> +                       for (j = 0; j < (PAGE_SIZE >> 2); ++j)
> > IMO PAGE_SIZE / sizeof(u32) is easier to understand.
>
> OK, will fix.
>
>
> >
> >> +                               iowrite32(ioread32(src++), dst++);
> >> +               }
> >> +               if (src_ops->unmap_local)
> >> +                       src_ops->unmap_local(src_iter, &src_map);
> >> +               if (dst_ops->unmap_local)
> >> +                       dst_ops->unmap_local(dst_iter, &dst_map);
> >> +       }
> >>   }
> >> +EXPORT_SYMBOL(ttm_move_memcpy);
> >>
> >>   int ttm_bo_move_memcpy(struct ttm_buffer_object *bo,
> >>                         struct ttm_operation_ctx *ctx,
> >> -                      struct ttm_resource *new_mem)
> >> +                      struct ttm_resource *dst_mem)
> >>   {
> >>          struct ttm_device *bdev = bo->bdev;
> >> -       struct ttm_resource_manager *man = ttm_manager_type(bdev, new_mem->mem_type);
> >> +       struct ttm_resource_manager *dst_man =
> >> +               ttm_manager_type(bo->bdev, dst_mem->mem_type);
> >>          struct ttm_tt *ttm = bo->ttm;
> >> -       struct ttm_resource *old_mem = &bo->mem;
> >> -       struct ttm_resource old_copy = *old_mem;
> >> -       void *old_iomap;
> >> -       void *new_iomap;
> >> +       struct ttm_resource *src_mem = &bo->mem;
> >> +       struct ttm_resource_manager *src_man =
> >> +               ttm_manager_type(bdev, src_mem->mem_type);
> >> +       struct ttm_resource src_copy = *src_mem;
> >> +       union {
> >> +               struct ttm_kmap_iter_tt tt;
> >> +               struct ttm_kmap_iter_linear_io io;
> >> +       } _dst_iter, _src_iter;
> >> +       struct ttm_kmap_iter *dst_iter, *src_iter;
> >>          int ret;
> >> -       unsigned long i;
> >>
> >> -       ret = ttm_bo_wait_ctx(bo, ctx);
> >> -       if (ret)
> >> -               return ret;
> >> -
> >> -       ret = ttm_resource_ioremap(bdev, old_mem, &old_iomap);
> >> -       if (ret)
> >> -               return ret;
> >> -       ret = ttm_resource_ioremap(bdev, new_mem, &new_iomap);
> >> -       if (ret)
> >> -               goto out;
> >> -
> >> -       /*
> >> -        * Single TTM move. NOP.
> >> -        */
> >> -       if (old_iomap == NULL && new_iomap == NULL)
> >> -               goto out2;
> >> -
> >> -       /*
> >> -        * Don't move nonexistent data. Clear destination instead.
> >> -        */
> >> -       if (old_iomap == NULL &&
> >> -           (ttm == NULL || (!ttm_tt_is_populated(ttm) &&
> >> -                            !(ttm->page_flags & TTM_PAGE_FLAG_SWAPPED)))) {
> >> -               memset_io(new_iomap, 0, new_mem->num_pages*PAGE_SIZE);
> >> -               goto out2;
> >> -       }
> >> -
> >> -       /*
> >> -        * TTM might be null for moves within the same region.
> >> -        */
> >> -       if (ttm) {
> >> +       if (ttm && ((ttm->page_flags & TTM_PAGE_FLAG_SWAPPED) ||
> >> +                   dst_man->use_tt)) {
> >>                  ret = ttm_tt_populate(bdev, ttm, ctx);
> >>                  if (ret)
> >> -                       goto out1;
> >> +                       return ret;
> >>          }
> >>
> >> -       for (i = 0; i < new_mem->num_pages; ++i) {
> >> -               if (old_iomap == NULL) {
> >> -                       pgprot_t prot = ttm_io_prot(bo, old_mem, PAGE_KERNEL);
> >> -                       ret = ttm_copy_ttm_io_page(ttm, new_iomap, i,
> >> -                                                  prot);
> >> -               } else if (new_iomap == NULL) {
> >> -                       pgprot_t prot = ttm_io_prot(bo, new_mem, PAGE_KERNEL);
> >> -                       ret = ttm_copy_io_ttm_page(ttm, old_iomap, i,
> >> -                                                  prot);
> >> -               } else {
> >> -                       ret = ttm_copy_io_page(new_iomap, old_iomap, i);
> >> -               }
> >> -               if (ret)
> >> -                       goto out1;
> >> +       dst_iter = ttm_kmap_iter_linear_io_init(&_dst_iter.io, bdev, dst_mem);
> >> +       if (PTR_ERR(dst_iter) == -EINVAL && dst_man->use_tt)
> >> +               dst_iter = ttm_kmap_iter_tt_init(&_dst_iter.tt, bo->ttm);
> >> +       if (IS_ERR(dst_iter))
> >> +               return PTR_ERR(dst_iter);
> >> +
> >> +       src_iter = ttm_kmap_iter_linear_io_init(&_src_iter.io, bdev, src_mem);
> >> +       if (PTR_ERR(src_iter) == -EINVAL && src_man->use_tt)
> >> +               src_iter = ttm_kmap_iter_tt_init(&_src_iter.tt, bo->ttm);
> >> +       if (IS_ERR(src_iter)) {
> >> +               ret = PTR_ERR(src_iter);
> >> +               goto out_src_iter;
> >>          }
> >> -       mb();
> >> -out2:
> >> -       old_copy = *old_mem;
> >>
> >> -       ttm_bo_assign_mem(bo, new_mem);
> >> -
> >> -       if (!man->use_tt)
> >> -               ttm_bo_tt_destroy(bo);
> >> +       ttm_move_memcpy(bo, dst_mem, dst_iter, src_iter);
> >> +       src_copy = *src_mem;
> >> +       ttm_bo_move_sync_cleanup(bo, dst_mem);
> >>
> >> -out1:
> >> -       ttm_resource_iounmap(bdev, old_mem, new_iomap);
> >> -out:
> >> -       ttm_resource_iounmap(bdev, &old_copy, old_iomap);
> >> +       if (!src_iter->ops->maps_tt)
> >> +               ttm_kmap_iter_linear_io_fini(&_src_iter.io, bdev, &src_copy);
> >> +out_src_iter:
> >> +       if (!dst_iter->ops->maps_tt)
> >> +               ttm_kmap_iter_linear_io_fini(&_dst_iter.io, bdev, dst_mem);
> >>
> >> -       /*
> >> -        * On error, keep the mm node!
> >> -        */
> >> -       if (!ret)
> >> -               ttm_resource_free(bo, &old_copy);
> >>          return ret;
> >>   }
> >>   EXPORT_SYMBOL(ttm_bo_move_memcpy);
> >> @@ -336,27 +272,7 @@ pgprot_t ttm_io_prot(struct ttm_buffer_object *bo, struct ttm_resource *res,
> >>          man = ttm_manager_type(bo->bdev, res->mem_type);
> >>          caching = man->use_tt ? bo->ttm->caching : res->bus.caching;
> >>
> >> -       /* Cached mappings need no adjustment */
> >> -       if (caching == ttm_cached)
> >> -               return tmp;
> >> -
> >> -#if defined(__i386__) || defined(__x86_64__)
> >> -       if (caching == ttm_write_combined)
> >> -               tmp = pgprot_writecombine(tmp);
> >> -       else if (boot_cpu_data.x86 > 3)
> >> -               tmp = pgprot_noncached(tmp);
> >> -#endif
> >> -#if defined(__ia64__) || defined(__arm__) || defined(__aarch64__) || \
> >> -    defined(__powerpc__) || defined(__mips__)
> >> -       if (caching == ttm_write_combined)
> >> -               tmp = pgprot_writecombine(tmp);
> >> -       else
> >> -               tmp = pgprot_noncached(tmp);
> >> -#endif
> >> -#if defined(__sparc__)
> >> -       tmp = pgprot_noncached(tmp);
> >> -#endif
> >> -       return tmp;
> >> +       return ttm_prot_from_caching(caching, tmp);
> >>   }
> >>   EXPORT_SYMBOL(ttm_io_prot);
> >>
> >> diff --git a/drivers/gpu/drm/ttm/ttm_module.c b/drivers/gpu/drm/ttm/ttm_module.c
> >> index 56b0efdba1a9..997c458f68a9 100644
> >> --- a/drivers/gpu/drm/ttm/ttm_module.c
> >> +++ b/drivers/gpu/drm/ttm/ttm_module.c
> >> @@ -31,12 +31,47 @@
> >>    */
> >>   #include <linux/module.h>
> >>   #include <linux/device.h>
> >> +#include <linux/pgtable.h>
> >>   #include <linux/sched.h>
> >>   #include <linux/debugfs.h>
> >>   #include <drm/drm_sysfs.h>
> >> +#include <drm/ttm/ttm_caching.h>
> >>
> >>   #include "ttm_module.h"
> >>
> >> +/**
> >> + * ttm_prot_from_caching - Modify the page protection according to the
> >> + * ttm cacing mode
> >> + * @caching: The ttm caching mode
> >> + * @tmp: The original page protection
> >> + *
> >> + * Return: The modified page protection
> >> + */
> >> +pgprot_t ttm_prot_from_caching(enum ttm_caching caching, pgprot_t tmp)
> >> +{
> >> +       /* Cached mappings need no adjustment */
> >> +       if (caching == ttm_cached)
> >> +               return tmp;
> >> +
> >> +#if defined(__i386__) || defined(__x86_64__)
> >> +       if (caching == ttm_write_combined)
> >> +               tmp = pgprot_writecombine(tmp);
> >> +       else if (boot_cpu_data.x86 > 3)
> >> +               tmp = pgprot_noncached(tmp);
> >> +#endif
> >> +#if defined(__ia64__) || defined(__arm__) || defined(__aarch64__) || \
> >> +       defined(__powerpc__) || defined(__mips__)
> >> +       if (caching == ttm_write_combined)
> >> +               tmp = pgprot_writecombine(tmp);
> >> +       else
> >> +               tmp = pgprot_noncached(tmp);
> >> +#endif
> >> +#if defined(__sparc__)
> >> +       tmp = pgprot_noncached(tmp);
> >> +#endif
> >> +       return tmp;
> >> +}
> >> +
> >>   struct dentry *ttm_debugfs_root;
> >>
> >>   static int __init ttm_init(void)
> >> diff --git a/drivers/gpu/drm/ttm/ttm_resource.c b/drivers/gpu/drm/ttm/ttm_resource.c
> >> index 59e2b7157e41..e05ae7e3d477 100644
> >> --- a/drivers/gpu/drm/ttm/ttm_resource.c
> >> +++ b/drivers/gpu/drm/ttm/ttm_resource.c
> >> @@ -22,6 +22,10 @@
> >>    * Authors: Christian König
> >>    */
> >>
> >> +#include <linux/dma-buf-map.h>
> >> +#include <linux/io-mapping.h>
> >> +#include <linux/scatterlist.h>
> >> +
> >>   #include <drm/ttm/ttm_resource.h>
> >>   #include <drm/ttm/ttm_bo_driver.h>
> >>
> >> @@ -147,3 +151,165 @@ void ttm_resource_manager_debug(struct ttm_resource_manager *man,
> >>                  man->func->debug(man, p);
> >>   }
> >>   EXPORT_SYMBOL(ttm_resource_manager_debug);
> >> +
> >> +static void ttm_kmap_iter_iomap_map_local(struct ttm_kmap_iter *iter,
> >> +                                         struct dma_buf_map *dmap,
> >> +                                         pgoff_t i)
> >> +{
> >> +       struct ttm_kmap_iter_iomap *iter_io =
> >> +               container_of(iter, typeof(*iter_io), base);
> >> +       void __iomem *addr;
> >> +
> >> +retry:
> >> +       while (i >= iter_io->cache.end) {
> >> +               iter_io->cache.sg = iter_io->cache.sg ?
> >> +                       sg_next(iter_io->cache.sg) : iter_io->st->sgl;
> >> +               iter_io->cache.i = iter_io->cache.end;
> >> +               iter_io->cache.end += sg_dma_len(iter_io->cache.sg) >>
> >> +                       PAGE_SHIFT;
> >> +               iter_io->cache.offs = sg_dma_address(iter_io->cache.sg) -
> >> +                       iter_io->start;
> >> +       }
> >> +
> >> +       if (i < iter_io->cache.i) {
> >> +               iter_io->cache.end = 0;
> >> +               iter_io->cache.sg = NULL;
> >> +               goto retry;
> >> +       }
> >> +
> >> +       addr = io_mapping_map_local_wc(iter_io->iomap, iter_io->cache.offs +
> >> +                                      (((resource_size_t)i - iter_io->cache.i)
> >> +                                       << PAGE_SHIFT));
> >> +       dma_buf_map_set_vaddr_iomem(dmap, addr);
> >> +}
> >> +
> >> +static void ttm_kmap_iter_iomap_unmap_local(struct ttm_kmap_iter *iter,
> >> +                                           struct dma_buf_map *map)
> >> +{
> >> +       io_mapping_unmap_local(map->vaddr_iomem);
> >> +}
> >> +
> >> +static const struct ttm_kmap_iter_ops ttm_kmap_iter_io_ops = {
> >> +       .map_local =  ttm_kmap_iter_iomap_map_local,
> >> +       .unmap_local = ttm_kmap_iter_iomap_unmap_local,
> >> +       .maps_tt = false,
> >> +};
> >> +
> >> +/**
> >> + * ttm_kmap_iter_iomap_init - Initialize a struct ttm_kmap_iter_iomap
> >> + * @iter_io: The struct ttm_kmap_iter_iomap to initialize.
> >> + * @iomap: The struct io_mapping representing the underlying linear io_memory.
> >> + * @st: sg_table into @iomap, representing the memory of the struct
> >> + * ttm_resource.
> >> + * @start: Offset that needs to be subtracted from @st to make
> >> + * sg_dma_address(st->sgl) - @start == 0 for @iomap start.
> >> + *
> >> + * Return: Pointer to the embedded struct ttm_kmap_iter.
> >> + */
> >> +struct ttm_kmap_iter *
> >> +ttm_kmap_iter_iomap_init(struct ttm_kmap_iter_iomap *iter_io,
> >> +                        struct io_mapping *iomap,
> >> +                        struct sg_table *st,
> >> +                        resource_size_t start)
> >> +{
> >> +       iter_io->base.ops = &ttm_kmap_iter_io_ops;
> >> +       iter_io->iomap = iomap;
> >> +       iter_io->st = st;
> >> +       iter_io->start = start;
> >> +       memset(&iter_io->cache, 0, sizeof(iter_io->cache));
> >> +
> >> +       return &iter_io->base;
> >> +}
> >> +EXPORT_SYMBOL(ttm_kmap_iter_iomap_init);
> >> +
> >> +/**
> >> + * DOC: Linear io iterator
> >> + *
> >> + * This code should die in the not too near future. Best would be if we could
> >> + * make io-mapping use memremap for all io memory, and have memremap
> >> + * implement a kmap_local functionality. We could then strip a huge amount of
> >> + * code. These linear io iterators are implemented to mimic old functionality,
> >> + * and they don't use kmap_local semantics at all internally. Rather ioremap or
> >> + * friends, and at least on 32-bit they add global TLB flushes and points
> >> + * of failure.
> >> + */
> >> +
> >> +static void ttm_kmap_iter_linear_io_map_local(struct ttm_kmap_iter *iter,
> >> +                                             struct dma_buf_map *dmap,
> >> +                                             pgoff_t i)
> >> +{
> >> +       struct ttm_kmap_iter_linear_io *iter_io =
> >> +               container_of(iter, typeof(*iter_io), base);
> >> +
> >> +       *dmap = iter_io->dmap;
> >> +       dma_buf_map_incr(dmap, i * PAGE_SIZE);
> >> +}
> >> +
> >> +static const struct ttm_kmap_iter_ops ttm_kmap_iter_linear_io_ops = {
> >> +       .map_local =  ttm_kmap_iter_linear_io_map_local,
> >> +       .maps_tt = false,
> >> +};
> >> +
> >> +struct ttm_kmap_iter *
> >> +ttm_kmap_iter_linear_io_init(struct ttm_kmap_iter_linear_io *iter_io,
> >> +                            struct ttm_device *bdev,
> >> +                            struct ttm_resource *mem)
> >> +{
> >> +       int ret;
> >> +
> >> +       ret = ttm_mem_io_reserve(bdev, mem);
> >> +       if (ret)
> >> +               goto out_err;
> >> +       if (!mem->bus.is_iomem) {
> >> +               ret = -EINVAL;
> >> +               goto out_io_free;
> >> +       }
> >> +
> >> +       if (mem->bus.addr) {
> >> +               dma_buf_map_set_vaddr(&iter_io->dmap, mem->bus.addr);
> >> +               iter_io->needs_unmap = false;
> >> +       } else {
> >> +               size_t bus_size = (size_t)mem->num_pages << PAGE_SHIFT;
> >> +
> >> +               iter_io->needs_unmap = true;
> >> +               if (mem->bus.caching == ttm_write_combined)
> >> +                       dma_buf_map_set_vaddr_iomem(&iter_io->dmap,
> >> +                                                   ioremap_wc(mem->bus.offset,
> >> +                                                              bus_size));
> >> +               else if (mem->bus.caching == ttm_cached)
> >> +                       dma_buf_map_set_vaddr(&iter_io->dmap,
> >> +                                             memremap(mem->bus.offset, bus_size,
> >> +                                                      MEMREMAP_WB));
> > The comments in set_vaddr suggest that this is meant for
> > system-memory. Does that actually matter or is it just about not
> > losing the __iomem annotation on platforms where it matters?
>
> Yes, it's the latter. dma_buf_map() is relatively new and the author
> probably didn't think about the case of cached iomem, which is used by,
> for example, vmwgfx.
>
> > Apparently cached device local is a thing. Also should this not be
> > wrapped in CONFIG_X86?
>
> Both dma_buf_map() and memremap are generic, I think, I guess memremap
> would return NULL if it's not supported.

It looks like memremap just wraps ioremap_cache, but since it also
discards the __iomem annotation should we be doing that universally?
Also not sure if ioremap_cache is universally supported, so wrapping
in CONFIG_X86 and falling back to plain ioremap() might be needed? Or
at least that looks like roughly what the previous code was doing? Not
too sure tbh.

>
> /Thomas
>
>