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, 61 insertions, 0 deletions

diff --git a/include/drm/ttm/ttm_kmap_iter.h b/include/drm/ttm/ttm_kmap_iter.h
new file mode 100644
index 000000000000..8bb00fd39d6c
--- /dev/null
+++ b/include/drm/ttm/ttm_kmap_iter.h
@@ -0,0 +1,61 @@
+/* SPDX-License-Identifier: MIT */
+/*
+ * Copyright © 2021 Intel Corporation
+ */
+#ifndef __TTM_KMAP_ITER_H__
+#define __TTM_KMAP_ITER_H__
+
+#include <linux/types.h>
+
+struct ttm_kmap_iter;
+struct dma_buf_map;
+
+/**
+ * struct ttm_kmap_iter_ops - Ops structure for a struct
+ * ttm_kmap_iter.
+ * @maps_tt: Whether the iterator maps TT memory directly, as opposed
+ * mapping a TT through an aperture. Both these modes have
+ * struct ttm_resource_manager::use_tt set, but the latter typically
+ * returns is_iomem == true from ttm_mem_io_reserve.
+ */
+struct ttm_kmap_iter_ops {
+	/**
+	 * kmap_local() - Map a PAGE_SIZE part of the resource using
+	 * kmap_local semantics.
+	 * @res_iter: Pointer to the struct ttm_kmap_iter representing
+	 * the resource.
+	 * @dmap: The struct dma_buf_map holding the virtual address after
+	 * the operation.
+	 * @i: The location within the resource to map. PAGE_SIZE granularity.
+	 */
+	void (*map_local)(struct ttm_kmap_iter *res_iter,
+			  struct dma_buf_map *dmap, pgoff_t i);
+	/**
+	 * unmap_local() - Unmap a PAGE_SIZE part of the resource previously
+	 * mapped using kmap_local.
+	 * @res_iter: Pointer to the struct ttm_kmap_iter representing
+	 * the resource.
+	 * @dmap: The struct dma_buf_map holding the virtual address after
+	 * the operation.
+	 */
+	void (*unmap_local)(struct ttm_kmap_iter *res_iter,
+			    struct dma_buf_map *dmap);
+	bool maps_tt;
+};
+
+/**
+ * struct ttm_kmap_iter - Iterator for kmap_local type operations on a
+ * resource.
+ * @ops: Pointer to the operations struct.
+ *
+ * This struct is intended to be embedded in a resource-specific specialization
+ * implementing operations for the resource.
+ *
+ * Nothing stops us from extending the operations to vmap, vmap_pfn etc,
+ * replacing some or parts of the ttm_bo_util. cpu-map functionality.
+ */
+struct ttm_kmap_iter {
+	const struct ttm_kmap_iter_ops *ops;
+};
+
+#endif /* __TTM_KMAP_ITER_H__ */