Re: [PATCH 3/6] drm/ttm: Support partial buffer mappings for ttm_bo_vmap()

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Hi

Am 14.06.24 um 16:33 schrieb Christian König:
Am 14.06.24 um 15:21 schrieb Thomas Zimmermann:
Add offset and size parameters to ttm_bo_vmap() to allow for partial
mappings of a buffer object. This brings the functionality on par with
ttm_bo_kmap().

Well the long term plan was to remove this functionality from ttm_bo_kmap() and nuke that function sooner or later.

What exactly is the use case for partial mappings?

I don't have a use case; except for streamlining the DRM internals.

For the drivers, xe uses partial mappings in i915_gem_object_read_from_page(). But struct iosys_map to map the whole buffer and do memcpys within the range. See patch 6 for that. I think it could do without partial mappings. Vmwgfx uses a local mappings at [1], but as the nearby comment says, this could be a TTM helper. Or maybe TTM could provide a dedicated ttm_bo_kmap_local_page() for temporary mappings like this one. There's also [2], which looks like a candidate for a possible ttm_bo_kmap_local_page(). And in vmwgfx, there's the memcpy at [3], which could be replaced with ttm_bo_vmap() plus iosys_map helpers. I think that's it. Best regards Thomas [1] https://elixir.bootlin.com/linux/v6.9/source/drivers/gpu/drm/vmwgfx/vmwgfx_cotable.c#L457 [2] https://elixir.bootlin.com/linux/v6.9/source/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c#L418 [3] https://elixir.bootlin.com/linux/v6.9/source/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c#L430

Regards,
Christian.


Callers pass the byte offset and size within the buffer object and
receive a page-aligned mapping of the buffer object's memory for the
specified area.

Also update all callers of ttm_bo_vmap() for the new parameters. As
before, existing callers map the buffer object's complete memory.

Signed-off-by: Thomas Zimmermann <tzimmermann@xxxxxxx>
---
  drivers/gpu/drm/drm_gem_ttm_helper.c  |  2 +-
  drivers/gpu/drm/drm_gem_vram_helper.c |  2 +-
  drivers/gpu/drm/loongson/lsdc_gem.c   |  2 +-
  drivers/gpu/drm/qxl/qxl_object.c      |  2 +-
  drivers/gpu/drm/ttm/ttm_bo_util.c     | 21 +++++++++++++++------
  drivers/gpu/drm/xe/xe_lrc.c           |  2 +-
  drivers/gpu/drm/xe/xe_vm.c            |  2 +-
  include/drm/ttm/ttm_bo.h              |  4 +++-
  8 files changed, 24 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem_ttm_helper.c b/drivers/gpu/drm/drm_gem_ttm_helper.c
index 3734aa2d1c5b5..f26b7c9077a68 100644
--- a/drivers/gpu/drm/drm_gem_ttm_helper.c
+++ b/drivers/gpu/drm/drm_gem_ttm_helper.c
@@ -67,7 +67,7 @@ int drm_gem_ttm_vmap(struct drm_gem_object *gem,
  {
      struct ttm_buffer_object *bo = drm_gem_ttm_of_gem(gem);
  -    return ttm_bo_vmap(bo, map);
+    return ttm_bo_vmap(bo, 0, gem->size, map);
  }
  EXPORT_SYMBOL(drm_gem_ttm_vmap);
  diff --git a/drivers/gpu/drm/drm_gem_vram_helper.c b/drivers/gpu/drm/drm_gem_vram_helper.c
index 6027584406af6..1670f9a459a9d 100644
--- a/drivers/gpu/drm/drm_gem_vram_helper.c
+++ b/drivers/gpu/drm/drm_gem_vram_helper.c
@@ -398,7 +398,7 @@ int drm_gem_vram_vmap(struct drm_gem_vram_object *gbo, struct iosys_map *map)
       * no mapping present.
       */
      if (iosys_map_is_null(&gbo->map)) {
-        ret = ttm_bo_vmap(&gbo->bo, &gbo->map);
+        ret = ttm_bo_vmap(&gbo->bo, 0, gbo->bo.base.size, &gbo->map);
          if (ret)
              return ret;
      }
diff --git a/drivers/gpu/drm/loongson/lsdc_gem.c b/drivers/gpu/drm/loongson/lsdc_gem.c
index a720d8f532093..f709960c781b9 100644
--- a/drivers/gpu/drm/loongson/lsdc_gem.c
+++ b/drivers/gpu/drm/loongson/lsdc_gem.c
@@ -77,7 +77,7 @@ static int lsdc_gem_object_vmap(struct drm_gem_object *obj, struct iosys_map *ma
          return ret;
      }
  -    ret = ttm_bo_vmap(tbo, &lbo->map);
+    ret = ttm_bo_vmap(tbo, 0, tbo->base.size, &lbo->map);
      if (ret) {
          drm_err(obj->dev, "ttm bo vmap failed\n");
          lsdc_bo_unpin(lbo);
diff --git a/drivers/gpu/drm/qxl/qxl_object.c b/drivers/gpu/drm/qxl/qxl_object.c
index 5893e27a7ae50..9f06d5e26a32c 100644
--- a/drivers/gpu/drm/qxl/qxl_object.c
+++ b/drivers/gpu/drm/qxl/qxl_object.c
@@ -164,7 +164,7 @@ int qxl_bo_vmap_locked(struct qxl_bo *bo, struct iosys_map *map)
          goto out;
      }
  -    r = ttm_bo_vmap(&bo->tbo, &bo->map);
+    r = ttm_bo_vmap(&bo->tbo, 0, bo->tbo.base.size, &bo->map);
      if (r) {
          qxl_bo_unpin_locked(bo);
          return r;
diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
index a9df0deff2deb..31f9772f05dac 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_util.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
@@ -457,17 +457,23 @@ EXPORT_SYMBOL(ttm_bo_kunmap);
   * ttm_bo_vmap
   *
   * @bo: The buffer object.
+ * @offset: Byte offset into the buffer.
+ * @size: Number of bytes to map.
   * @map: pointer to a struct iosys_map representing the map.
   *
   * Sets up a kernel virtual mapping, using ioremap or vmap to the
   * data in the buffer object. The parameter @map returns the virtual
   * address as struct iosys_map. Unmap the buffer with ttm_bo_vunmap().
+ * The address stored in @map will be aligned to the next lower page
+ * boundaries.
   *
   * Returns
   * -ENOMEM: Out of memory.
   * -EINVAL: Invalid range.
   */
-int ttm_bo_vmap(struct ttm_buffer_object *bo, struct iosys_map *map)
+int ttm_bo_vmap(struct ttm_buffer_object *bo,
+        unsigned long offset, unsigned long size,
+        struct iosys_map *map)
  {
      struct ttm_resource *mem = bo->resource;
      int ret;
@@ -483,18 +489,18 @@ int ttm_bo_vmap(struct ttm_buffer_object *bo, struct iosys_map *map)
          u16 alloc_flags;
            if (mem->bus.addr) {
-            vaddr_iomem = (void __iomem *)mem->bus.addr;
+            vaddr_iomem = (u8 __iomem *)mem->bus.addr + offset;
              alloc_flags = ttm_bo_map_premapped;
          } else if (mem->bus.caching == ttm_write_combined) {
-            vaddr_iomem = ioremap_wc(mem->bus.offset, bo->base.size);
+            vaddr_iomem = ioremap_wc(mem->bus.offset + offset, size);
              alloc_flags = ttm_bo_map_iomap;
  #ifdef CONFIG_X86
          } else if (mem->bus.caching == ttm_cached) {
-            vaddr_iomem = ioremap_cache(mem->bus.offset, bo->base.size); +            vaddr_iomem = ioremap_cache(mem->bus.offset + offset, size);
              alloc_flags = ttm_bo_map_iomap;
  #endif
          } else {
-            vaddr_iomem = ioremap(mem->bus.offset, bo->base.size);
+            vaddr_iomem = ioremap(mem->bus.offset + offset, size);
              alloc_flags = ttm_bo_map_iomap;
          }
  @@ -510,6 +516,9 @@ int ttm_bo_vmap(struct ttm_buffer_object *bo, struct iosys_map *map)
              .no_wait_gpu = false
          };
          struct ttm_tt *ttm = bo->ttm;
+        unsigned long start_page = offset >> PAGE_SHIFT;
+        unsigned long aligned_size = size + (offset - (start_page << PAGE_SHIFT)); +        unsigned long num_pages = DIV_ROUND_UP(aligned_size, PAGE_SIZE);
          pgprot_t prot;
          void *vaddr;
          u16 alloc_flags;
@@ -523,7 +532,7 @@ int ttm_bo_vmap(struct ttm_buffer_object *bo, struct iosys_map *map)
           * or to make the buffer object look contiguous.
           */
          prot = ttm_io_prot(bo, mem, PAGE_KERNEL);
-        vaddr = vmap(ttm->pages, ttm->num_pages, 0, prot);
+        vaddr = vmap(ttm->pages + start_page, num_pages, 0, prot);
          if (!vaddr)
              return -ENOMEM;
          alloc_flags = ttm_bo_map_vmap;
diff --git a/drivers/gpu/drm/xe/xe_lrc.c b/drivers/gpu/drm/xe/xe_lrc.c
index c1bb85d2e243f..3a68fe6d592ed 100644
--- a/drivers/gpu/drm/xe/xe_lrc.c
+++ b/drivers/gpu/drm/xe/xe_lrc.c
@@ -1595,7 +1595,7 @@ void xe_lrc_snapshot_capture_delayed(struct xe_lrc_snapshot *snapshot)
          goto put_bo;
        xe_bo_lock(bo, false);
-    if (!ttm_bo_vmap(&bo->ttm, &src)) {
+    if (!ttm_bo_vmap(&bo->ttm, 0, bo->ttm.base.size, &src)) {
          xe_map_memcpy_from(xe_bo_device(bo),
                     snapshot->lrc_snapshot, &src, snapshot->lrc_offset,
                     snapshot->lrc_size);
diff --git a/drivers/gpu/drm/xe/xe_vm.c b/drivers/gpu/drm/xe/xe_vm.c
index 99bf7412475c0..81306c32f5d09 100644
--- a/drivers/gpu/drm/xe/xe_vm.c
+++ b/drivers/gpu/drm/xe/xe_vm.c
@@ -3485,7 +3485,7 @@ void xe_vm_snapshot_capture_delayed(struct xe_vm_snapshot *snap)
            if (bo) {
              xe_bo_lock(bo, false);
-            err = ttm_bo_vmap(&bo->ttm, &src);
+            err = ttm_bo_vmap(&bo->ttm, 0, bo->ttm.base.size, &src);
              if (!err) {
                  xe_map_memcpy_from(xe_bo_device(bo),
                             snap->snap[i].data,
diff --git a/include/drm/ttm/ttm_bo.h b/include/drm/ttm/ttm_bo.h
index 6ccf96c91f3ae..c421ffe3563b1 100644
--- a/include/drm/ttm/ttm_bo.h
+++ b/include/drm/ttm/ttm_bo.h
@@ -375,7 +375,9 @@ int ttm_bo_init_validate(struct ttm_device *bdev, struct ttm_buffer_object *bo,   int ttm_bo_kmap(struct ttm_buffer_object *bo, unsigned long start_page,
          unsigned long num_pages, struct ttm_bo_kmap_obj *map);
  void ttm_bo_kunmap(struct ttm_bo_kmap_obj *map);
-int ttm_bo_vmap(struct ttm_buffer_object *bo, struct iosys_map *map);
+int ttm_bo_vmap(struct ttm_buffer_object *bo,
+        unsigned long offset, unsigned long size,
+        struct iosys_map *map);
  void ttm_bo_vunmap(struct ttm_buffer_object *bo, struct iosys_map *map);   int ttm_bo_mmap_obj(struct vm_area_struct *vma, struct ttm_buffer_object *bo);   int ttm_bo_swapout(struct ttm_buffer_object *bo, struct ttm_operation_ctx *ctx,


--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)




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