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dma-mapping: add a dma_ops_bypass flag to struct device
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Several IOMMU drivers have a bypass mode where they can use a direct
mapping if the devices DMA mask is large enough.  Add generic support
to the core dma-mapping code to do that to switch those drivers to
a common solution.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
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Christoph Hellwig committed Jul 19, 2020
1 parent 2f9237d commit d35834c
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Showing 3 changed files with 68 additions and 22 deletions.
8 changes: 8 additions & 0 deletions include/linux/device.h
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Original file line number Diff line number Diff line change
Expand Up @@ -523,6 +523,11 @@ struct dev_links_info {
* sync_state() callback.
* @dma_coherent: this particular device is dma coherent, even if the
* architecture supports non-coherent devices.
* @dma_ops_bypass: If set to %true then the dma_ops are bypassed for the
* streaming DMA operations (->map_* / ->unmap_* / ->sync_*),
* and optionall (if the coherent mask is large enough) also
* for dma allocations. This flag is managed by the dma ops
* instance from ->dma_supported.
*
* At the lowest level, every device in a Linux system is represented by an
* instance of struct device. The device structure contains the information
Expand Down Expand Up @@ -623,6 +628,9 @@ struct device {
defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU_ALL)
bool dma_coherent:1;
#endif
#ifdef CONFIG_DMA_OPS_BYPASS
bool dma_ops_bypass : 1;
#endif
};

static inline struct device *kobj_to_dev(struct kobject *kobj)
Expand Down
8 changes: 8 additions & 0 deletions kernel/dma/Kconfig
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,14 @@ config HAS_DMA
config DMA_OPS
bool

#
# IOMMU drivers that can bypass the IOMMU code and optionally use the direct
# mapping fast path should select this option and set the dma_ops_bypass
# flag in struct device where applicable
#
config DMA_OPS_BYPASS
bool

config NEED_SG_DMA_LENGTH
bool

Expand Down
74 changes: 52 additions & 22 deletions kernel/dma/mapping.c
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Original file line number Diff line number Diff line change
Expand Up @@ -105,9 +105,35 @@ void *dmam_alloc_attrs(struct device *dev, size_t size, dma_addr_t *dma_handle,
}
EXPORT_SYMBOL(dmam_alloc_attrs);

static inline bool dma_is_direct(const struct dma_map_ops *ops)
static bool dma_go_direct(struct device *dev, dma_addr_t mask,
const struct dma_map_ops *ops)
{
return likely(!ops);
if (likely(!ops))
return true;
#ifdef CONFIG_DMA_OPS_BYPASS
if (dev->dma_ops_bypass)
return min_not_zero(mask, dev->bus_dma_limit) >=
dma_direct_get_required_mask(dev);
#endif
return false;
}


/*
* Check if the devices uses a direct mapping for streaming DMA operations.
* This allows IOMMU drivers to set a bypass mode if the DMA mask is large
* enough.
*/
static inline bool dma_alloc_direct(struct device *dev,
const struct dma_map_ops *ops)
{
return dma_go_direct(dev, dev->coherent_dma_mask, ops);
}

static inline bool dma_map_direct(struct device *dev,
const struct dma_map_ops *ops)
{
return dma_go_direct(dev, *dev->dma_mask, ops);
}

dma_addr_t dma_map_page_attrs(struct device *dev, struct page *page,
Expand All @@ -118,7 +144,7 @@ dma_addr_t dma_map_page_attrs(struct device *dev, struct page *page,
dma_addr_t addr;

BUG_ON(!valid_dma_direction(dir));
if (dma_is_direct(ops))
if (dma_map_direct(dev, ops))
addr = dma_direct_map_page(dev, page, offset, size, dir, attrs);
else
addr = ops->map_page(dev, page, offset, size, dir, attrs);
Expand All @@ -134,7 +160,7 @@ void dma_unmap_page_attrs(struct device *dev, dma_addr_t addr, size_t size,
const struct dma_map_ops *ops = get_dma_ops(dev);

BUG_ON(!valid_dma_direction(dir));
if (dma_is_direct(ops))
if (dma_map_direct(dev, ops))
dma_direct_unmap_page(dev, addr, size, dir, attrs);
else if (ops->unmap_page)
ops->unmap_page(dev, addr, size, dir, attrs);
Expand All @@ -153,7 +179,7 @@ int dma_map_sg_attrs(struct device *dev, struct scatterlist *sg, int nents,
int ents;

BUG_ON(!valid_dma_direction(dir));
if (dma_is_direct(ops))
if (dma_map_direct(dev, ops))
ents = dma_direct_map_sg(dev, sg, nents, dir, attrs);
else
ents = ops->map_sg(dev, sg, nents, dir, attrs);
Expand All @@ -172,7 +198,7 @@ void dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sg,

BUG_ON(!valid_dma_direction(dir));
debug_dma_unmap_sg(dev, sg, nents, dir);
if (dma_is_direct(ops))
if (dma_map_direct(dev, ops))
dma_direct_unmap_sg(dev, sg, nents, dir, attrs);
else if (ops->unmap_sg)
ops->unmap_sg(dev, sg, nents, dir, attrs);
Expand All @@ -191,7 +217,7 @@ dma_addr_t dma_map_resource(struct device *dev, phys_addr_t phys_addr,
if (WARN_ON_ONCE(pfn_valid(PHYS_PFN(phys_addr))))
return DMA_MAPPING_ERROR;

if (dma_is_direct(ops))
if (dma_map_direct(dev, ops))
addr = dma_direct_map_resource(dev, phys_addr, size, dir, attrs);
else if (ops->map_resource)
addr = ops->map_resource(dev, phys_addr, size, dir, attrs);
Expand All @@ -207,7 +233,7 @@ void dma_unmap_resource(struct device *dev, dma_addr_t addr, size_t size,
const struct dma_map_ops *ops = get_dma_ops(dev);

BUG_ON(!valid_dma_direction(dir));
if (!dma_is_direct(ops) && ops->unmap_resource)
if (!dma_map_direct(dev, ops) && ops->unmap_resource)
ops->unmap_resource(dev, addr, size, dir, attrs);
debug_dma_unmap_resource(dev, addr, size, dir);
}
Expand All @@ -219,7 +245,7 @@ void dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr, size_t size,
const struct dma_map_ops *ops = get_dma_ops(dev);

BUG_ON(!valid_dma_direction(dir));
if (dma_is_direct(ops))
if (dma_map_direct(dev, ops))
dma_direct_sync_single_for_cpu(dev, addr, size, dir);
else if (ops->sync_single_for_cpu)
ops->sync_single_for_cpu(dev, addr, size, dir);
Expand All @@ -233,7 +259,7 @@ void dma_sync_single_for_device(struct device *dev, dma_addr_t addr,
const struct dma_map_ops *ops = get_dma_ops(dev);

BUG_ON(!valid_dma_direction(dir));
if (dma_is_direct(ops))
if (dma_map_direct(dev, ops))
dma_direct_sync_single_for_device(dev, addr, size, dir);
else if (ops->sync_single_for_device)
ops->sync_single_for_device(dev, addr, size, dir);
Expand All @@ -247,7 +273,7 @@ void dma_sync_sg_for_cpu(struct device *dev, struct scatterlist *sg,
const struct dma_map_ops *ops = get_dma_ops(dev);

BUG_ON(!valid_dma_direction(dir));
if (dma_is_direct(ops))
if (dma_map_direct(dev, ops))
dma_direct_sync_sg_for_cpu(dev, sg, nelems, dir);
else if (ops->sync_sg_for_cpu)
ops->sync_sg_for_cpu(dev, sg, nelems, dir);
Expand All @@ -261,7 +287,7 @@ void dma_sync_sg_for_device(struct device *dev, struct scatterlist *sg,
const struct dma_map_ops *ops = get_dma_ops(dev);

BUG_ON(!valid_dma_direction(dir));
if (dma_is_direct(ops))
if (dma_map_direct(dev, ops))
dma_direct_sync_sg_for_device(dev, sg, nelems, dir);
else if (ops->sync_sg_for_device)
ops->sync_sg_for_device(dev, sg, nelems, dir);
Expand Down Expand Up @@ -302,7 +328,7 @@ int dma_get_sgtable_attrs(struct device *dev, struct sg_table *sgt,
{
const struct dma_map_ops *ops = get_dma_ops(dev);

if (dma_is_direct(ops))
if (dma_alloc_direct(dev, ops))
return dma_direct_get_sgtable(dev, sgt, cpu_addr, dma_addr,
size, attrs);
if (!ops->get_sgtable)
Expand Down Expand Up @@ -372,7 +398,7 @@ bool dma_can_mmap(struct device *dev)
{
const struct dma_map_ops *ops = get_dma_ops(dev);

if (dma_is_direct(ops))
if (dma_alloc_direct(dev, ops))
return dma_direct_can_mmap(dev);
return ops->mmap != NULL;
}
Expand All @@ -397,7 +423,7 @@ int dma_mmap_attrs(struct device *dev, struct vm_area_struct *vma,
{
const struct dma_map_ops *ops = get_dma_ops(dev);

if (dma_is_direct(ops))
if (dma_alloc_direct(dev, ops))
return dma_direct_mmap(dev, vma, cpu_addr, dma_addr, size,
attrs);
if (!ops->mmap)
Expand All @@ -410,7 +436,7 @@ u64 dma_get_required_mask(struct device *dev)
{
const struct dma_map_ops *ops = get_dma_ops(dev);

if (dma_is_direct(ops))
if (dma_alloc_direct(dev, ops))
return dma_direct_get_required_mask(dev);
if (ops->get_required_mask)
return ops->get_required_mask(dev);
Expand Down Expand Up @@ -441,7 +467,7 @@ void *dma_alloc_attrs(struct device *dev, size_t size, dma_addr_t *dma_handle,
/* let the implementation decide on the zone to allocate from: */
flag &= ~(__GFP_DMA | __GFP_DMA32 | __GFP_HIGHMEM);

if (dma_is_direct(ops))
if (dma_alloc_direct(dev, ops))
cpu_addr = dma_direct_alloc(dev, size, dma_handle, flag, attrs);
else if (ops->alloc)
cpu_addr = ops->alloc(dev, size, dma_handle, flag, attrs);
Expand Down Expand Up @@ -473,7 +499,7 @@ void dma_free_attrs(struct device *dev, size_t size, void *cpu_addr,
return;

debug_dma_free_coherent(dev, size, cpu_addr, dma_handle);
if (dma_is_direct(ops))
if (dma_alloc_direct(dev, ops))
dma_direct_free(dev, size, cpu_addr, dma_handle, attrs);
else if (ops->free)
ops->free(dev, size, cpu_addr, dma_handle, attrs);
Expand All @@ -484,7 +510,11 @@ int dma_supported(struct device *dev, u64 mask)
{
const struct dma_map_ops *ops = get_dma_ops(dev);

if (dma_is_direct(ops))
/*
* ->dma_supported sets the bypass flag, so we must always call
* into the method here unless the device is truly direct mapped.
*/
if (!ops)
return dma_direct_supported(dev, mask);
if (!ops->dma_supported)
return 1;
Expand Down Expand Up @@ -540,7 +570,7 @@ void dma_cache_sync(struct device *dev, void *vaddr, size_t size,

BUG_ON(!valid_dma_direction(dir));

if (dma_is_direct(ops))
if (dma_alloc_direct(dev, ops))
arch_dma_cache_sync(dev, vaddr, size, dir);
else if (ops->cache_sync)
ops->cache_sync(dev, vaddr, size, dir);
Expand All @@ -552,7 +582,7 @@ size_t dma_max_mapping_size(struct device *dev)
const struct dma_map_ops *ops = get_dma_ops(dev);
size_t size = SIZE_MAX;

if (dma_is_direct(ops))
if (dma_map_direct(dev, ops))
size = dma_direct_max_mapping_size(dev);
else if (ops && ops->max_mapping_size)
size = ops->max_mapping_size(dev);
Expand All @@ -565,7 +595,7 @@ bool dma_need_sync(struct device *dev, dma_addr_t dma_addr)
{
const struct dma_map_ops *ops = get_dma_ops(dev);

if (dma_is_direct(ops))
if (dma_map_direct(dev, ops))
return dma_direct_need_sync(dev, dma_addr);
return ops->sync_single_for_cpu || ops->sync_single_for_device;
}
Expand Down

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