Re: [PATCH v4 05/10] drm/ttm: Add vmap/vunmap to TTM and TTM GEM helpers

Christian König <christian.koenig@xxxxxxx> · Mon, 19 Oct 2020 11:45:05 +0200

Hi Thomas,

[SNIP]
   +int ttm_bo_vmap(struct ttm_buffer_object *bo, struct dma_buf_map *map)
+{
+    struct ttm_resource *mem = &bo->mem;
+    int ret;
+
+    ret = ttm_mem_io_reserve(bo->bdev, mem);
+    if (ret)
+        return ret;
+
+    if (mem->bus.is_iomem) {
+        void __iomem *vaddr_iomem;
+        unsigned long size = bo->num_pages << PAGE_SHIFT;
Please use uint64_t here and make sure to cast bo->num_pages before
shifting.
I thought the rule of thumb is to use u64 in source code. Yet TTM only
uses uint*_t types. Is there anything special about TTM?

My last status is that you can use both and my personal preference is to 
use the uint*_t types because they are part of a higher level standard.

We have an unit tests of allocating a 8GB BO and that should work on a
32bit machine as well :)

+
+        if (mem->bus.addr)
+            vaddr_iomem = (void *)(((u8 *)mem->bus.addr));
I after reading the patch again, I realized that this is the
'ttm_bo_map_premapped' case and it's missing from _vunmap(). I see two
options here: ignore this case in _vunmap(), or do an ioremap()
unconditionally. Which one is preferable?

ioremap would be very very bad, so we should just do nothing.

Thanks,
Christian.


Best regards
Thomas

+        else if (mem->placement & TTM_PL_FLAG_WC)
I've just nuked the TTM_PL_FLAG_WC flag in drm-misc-next. There is a new
mem->bus.caching enum as replacement.

+            vaddr_iomem = ioremap_wc(mem->bus.offset, size);
+        else
+            vaddr_iomem = ioremap(mem->bus.offset, size);
+
+        if (!vaddr_iomem)
+            return -ENOMEM;
+
+        dma_buf_map_set_vaddr_iomem(map, vaddr_iomem);
+
+    } else {
+        struct ttm_operation_ctx ctx = {
+            .interruptible = false,
+            .no_wait_gpu = false
+        };
+        struct ttm_tt *ttm = bo->ttm;
+        pgprot_t prot;
+        void *vaddr;
+
+        BUG_ON(!ttm);
I think we can drop this, populate will just crash badly anyway.

+
+        ret = ttm_tt_populate(bo->bdev, ttm, &ctx);
+        if (ret)
+            return ret;
+
+        /*
+         * We need to use vmap to get the desired page protection
+         * or to make the buffer object look contiguous.
+         */
+        prot = ttm_io_prot(mem->placement, PAGE_KERNEL);
The calling convention has changed on drm-misc-next as well, but should
be trivial to adapt.

Regards,
Christian.

+        vaddr = vmap(ttm->pages, bo->num_pages, 0, prot);
+        if (!vaddr)
+            return -ENOMEM;
+
+        dma_buf_map_set_vaddr(map, vaddr);
+    }
+
+    return 0;
+}
+EXPORT_SYMBOL(ttm_bo_vmap);
+
+void ttm_bo_vunmap(struct ttm_buffer_object *bo, struct dma_buf_map
*map)
+{
+    if (dma_buf_map_is_null(map))
+        return;
+
+    if (map->is_iomem)
+        iounmap(map->vaddr_iomem);
+    else
+        vunmap(map->vaddr);
+    dma_buf_map_clear(map);
+
+    ttm_mem_io_free(bo->bdev, &bo->mem);
+}
+EXPORT_SYMBOL(ttm_bo_vunmap);
+
   static int ttm_bo_wait_free_node(struct ttm_buffer_object *bo,
                    bool dst_use_tt)
   {

diff --git a/include/drm/drm_gem_ttm_helper.h
b/include/drm/drm_gem_ttm_helper.h
index 118cef76f84f..7c6d874910b8 100644
--- a/include/drm/drm_gem_ttm_helper.h
+++ b/include/drm/drm_gem_ttm_helper.h
@@ -10,11 +10,17 @@
   #include <drm/ttm/ttm_bo_api.h>
   #include <drm/ttm/ttm_bo_driver.h>
   +struct dma_buf_map;
+
   #define drm_gem_ttm_of_gem(gem_obj) \
       container_of(gem_obj, struct ttm_buffer_object, base)
     void drm_gem_ttm_print_info(struct drm_printer *p, unsigned int
indent,
                   const struct drm_gem_object *gem);
+int drm_gem_ttm_vmap(struct drm_gem_object *gem,
+             struct dma_buf_map *map);
+void drm_gem_ttm_vunmap(struct drm_gem_object *gem,
+            struct dma_buf_map *map);
   int drm_gem_ttm_mmap(struct drm_gem_object *gem,
                struct vm_area_struct *vma);
   diff --git a/include/drm/ttm/ttm_bo_api.h
b/include/drm/ttm/ttm_bo_api.h
index 37102e45e496..2c59a785374c 100644
--- a/include/drm/ttm/ttm_bo_api.h
+++ b/include/drm/ttm/ttm_bo_api.h
@@ -48,6 +48,8 @@ struct ttm_bo_global;
     struct ttm_bo_device;
   +struct dma_buf_map;
+
   struct drm_mm_node;
     struct ttm_placement;
@@ -494,6 +496,32 @@ int ttm_bo_kmap(struct ttm_buffer_object *bo,
unsigned long start_page,
    */
   void ttm_bo_kunmap(struct ttm_bo_kmap_obj *map);
   +/**
+ * ttm_bo_vmap
+ *
+ * @bo: The buffer object.
+ * @map: pointer to a struct dma_buf_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 dma_buf_map. Unmap the buffer with ttm_bo_vunmap().
+ *
+ * Returns
+ * -ENOMEM: Out of memory.
+ * -EINVAL: Invalid range.
+ */
+int ttm_bo_vmap(struct ttm_buffer_object *bo, struct dma_buf_map *map);
+
+/**
+ * ttm_bo_vunmap
+ *
+ * @bo: The buffer object.
+ * @map: Object describing the map to unmap.
+ *
+ * Unmaps a kernel map set up by ttm_bo_vmap().
+ */
+void ttm_bo_vunmap(struct ttm_buffer_object *bo, struct dma_buf_map
*map);
+
   /**
    * ttm_bo_mmap_obj - mmap memory backed by a ttm buffer object.
    *
diff --git a/include/linux/dma-buf-map.h b/include/linux/dma-buf-map.h
index fd1aba545fdf..2e8bbecb5091 100644
--- a/include/linux/dma-buf-map.h
+++ b/include/linux/dma-buf-map.h
@@ -45,6 +45,12 @@
    *
    *    dma_buf_map_set_vaddr(&map. 0xdeadbeaf);
    *
+ * To set an address in I/O memory, use dma_buf_map_set_vaddr_iomem().
+ *
+ * .. code-block:: c
+ *
+ *    dma_buf_map_set_vaddr_iomem(&map. 0xdeadbeaf);
+ *
    * Test if a mapping is valid with either dma_buf_map_is_set() or
    * dma_buf_map_is_null().
    *
@@ -118,6 +124,20 @@ static inline void dma_buf_map_set_vaddr(struct
dma_buf_map *map, void *vaddr)
       map->is_iomem = false;
   }
   +/**
+ * dma_buf_map_set_vaddr_iomem - Sets a dma-buf mapping structure to
an address in I/O memory
+ * @map:        The dma-buf mapping structure
+ * @vaddr_iomem:    An I/O-memory address
+ *
+ * Sets the address and the I/O-memory flag.
+ */
+static inline void dma_buf_map_set_vaddr_iomem(struct dma_buf_map *map,
+                           void __iomem *vaddr_iomem)
+{
+    map->vaddr_iomem = vaddr_iomem;
+    map->is_iomem = true;
+}
+
   /**
    * dma_buf_map_is_equal - Compares two dma-buf mapping structures
for equality
    * @lhs:    The dma-buf mapping structure
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