linux-stable/include/drm/ttm/ttm_kmap_iter.h
Thomas Hellström 3bf3710e37 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
2021-06-07 16:07:08 +02:00

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1.8 KiB
C

/* 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__ */