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

Thomas Hellström thomas.hellstrom at linux.intel.com
Tue May 25 09:32:40 UTC 2021


On 5/25/21 11:18 AM, Matthew Auld wrote:
> On Fri, 21 May 2021 at 16:33, Thomas Hellström
> <thomas.hellstrom at 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 at amd.com>
>> Signed-off-by: Thomas Hellström <thomas.hellstrom at 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.

/Thomas




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