drm/ttm: Add a generic TTM memcpy move for page-based iomem

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>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://lore.kernel.org/r/20210602083818.241793-4-thomas.hellstrom@linux.intel.com

1 files changed, 45 insertions, 0 deletions

diff --git a/drivers/gpu/drm/ttm/ttm_tt.c b/drivers/gpu/drm/ttm/ttm_tt.c
index 682c840c9a51..24031a8acd2d 100644
--- a/drivers/gpu/drm/ttm/ttm_tt.c
+++ b/drivers/gpu/drm/ttm/ttm_tt.c
@@ -433,3 +433,48 @@ void ttm_tt_mgr_init(unsigned long num_pages, unsigned long num_dma32_pages)
 	if (!ttm_dma32_pages_limit)
 		ttm_dma32_pages_limit = num_dma32_pages;
 }
+
+static void ttm_kmap_iter_tt_map_local(struct ttm_kmap_iter *iter,
+				       struct dma_buf_map *dmap,
+				       pgoff_t i)
+{
+	struct ttm_kmap_iter_tt *iter_tt =
+		container_of(iter, typeof(*iter_tt), base);
+
+	dma_buf_map_set_vaddr(dmap, kmap_local_page_prot(iter_tt->tt->pages[i],
+							 iter_tt->prot));
+}
+
+static void ttm_kmap_iter_tt_unmap_local(struct ttm_kmap_iter *iter,
+					 struct dma_buf_map *map)
+{
+	kunmap_local(map->vaddr);
+}
+
+static const struct ttm_kmap_iter_ops ttm_kmap_iter_tt_ops = {
+	.map_local = ttm_kmap_iter_tt_map_local,
+	.unmap_local = ttm_kmap_iter_tt_unmap_local,
+	.maps_tt = true,
+};
+
+/**
+ * ttm_kmap_iter_tt_init - Initialize a struct ttm_kmap_iter_tt
+ * @iter_tt: The struct ttm_kmap_iter_tt to initialize.
+ * @tt: Struct ttm_tt holding page pointers of the struct ttm_resource.
+ *
+ * Return: Pointer to the embedded struct ttm_kmap_iter.
+ */
+struct ttm_kmap_iter *
+ttm_kmap_iter_tt_init(struct ttm_kmap_iter_tt *iter_tt,
+		      struct ttm_tt *tt)
+{
+	iter_tt->base.ops = &ttm_kmap_iter_tt_ops;
+	iter_tt->tt = tt;
+	if (tt)
+		iter_tt->prot = ttm_prot_from_caching(tt->caching, PAGE_KERNEL);
+	else
+		iter_tt->prot = PAGE_KERNEL;
+
+	return &iter_tt->base;
+}
+EXPORT_SYMBOL(ttm_kmap_iter_tt_init);