dma-mapping: remove an outdated comment from dma-map-ops.h

The "/* CONFIG_ARCH_HAS_DMA_COHERENCE_H */" was an description about the
ARCH_HAS_DMA_COHERENCE_H configure option, but it has been removed

dma-mapping: remove an outdated comment from dma-map-ops.h

The "/* CONFIG_ARCH_HAS_DMA_COHERENCE_H */" was an description about the
ARCH_HAS_DMA_COHERENCE_H configure option, but it has been removed since
the dma_default_coherent variable was lifted from the mips architecture
to the driver core. Therefore it doesn't match any compile guard now.
Just remove it.

Fixes: 6d4e9a8efe3d ("driver core: lift dma_default_coherent into common code")
Signed-off-by: Sui Jingfeng <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>

show more ...

dma-mapping: fix vmap and mmap of noncontiougs allocations

Commit b5c58b2fdc42 ("dma-mapping: direct calls for dma-iommu") switched
to use direct calls to dma-iommu, but missed the dma_vmap_nonconti

dma-mapping: fix vmap and mmap of noncontiougs allocations

Commit b5c58b2fdc42 ("dma-mapping: direct calls for dma-iommu") switched
to use direct calls to dma-iommu, but missed the dma_vmap_noncontiguous,
dma_vunmap_noncontiguous and dma_mmap_noncontiguous behavior keyed off the
presence of the alloc_noncontiguous method.

Fix this by removing the now unused alloc_noncontiguous and
free_noncontiguous methods and moving the vmapping and mmaping of the
noncontiguous allocations into the iommu code, as it is the only provider
of actually noncontiguous allocations.

Fixes: b5c58b2fdc42 ("dma-mapping: direct calls for dma-iommu")
Reported-by: Xi Ruoyao <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Leon Romanovsky <[email protected]>
Tested-by: Xi Ruoyao <[email protected]>

show more ...

dma-mapping: clearly mark DMA ops as an architecture feature

DMA ops are a helper for architectures and not for drivers to override
the DMA implementation.

Unfortunately driver authors keep ignorin

dma-mapping: clearly mark DMA ops as an architecture feature

DMA ops are a helper for architectures and not for drivers to override
the DMA implementation.

Unfortunately driver authors keep ignoring this. Make the fact more
clear by renaming the symbol to ARCH_HAS_DMA_OPS and having the two drivers
overriding their dma_ops depend on that. These drivers should probably be
marked broken, but we can give them a bit of a grace period for that.

Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Thomas Gleixner <[email protected]>
Acked-by: Sakari Ailus <[email protected]> # for IPU6
Acked-by: Robin Murphy <[email protected]>

show more ...

dma-mapping: direct calls for dma-iommu

Directly call into dma-iommu just like we have been doing for dma-direct
for a while. This avoids the indirect call overhead for IOMMU ops and
removes the ne

dma-mapping: direct calls for dma-iommu

Directly call into dma-iommu just like we have been doing for dma-direct
for a while. This avoids the indirect call overhead for IOMMU ops and
removes the need to have DMA ops entirely for many common configurations.

Signed-off-by: Leon Romanovsky <[email protected]>
Signed-off-by: Leon Romanovsky <[email protected]>
Acked-by: Greg Kroah-Hartman <[email protected]>
Acked-by: Robin Murphy <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>

show more ...

dma: fix DMA sync for drivers not calling dma_set_mask*()

There are several reports that the DMA sync shortcut broke non-coherent
devices.
dev->dma_need_sync is false after the &device allocation an

dma: fix DMA sync for drivers not calling dma_set_mask*()

There are several reports that the DMA sync shortcut broke non-coherent
devices.
dev->dma_need_sync is false after the &device allocation and if a driver
didn't call dma_set_mask*(), it will still be false even if the device
is not DMA-coherent and thus needs synchronizing. Due to historical
reasons, there's still a lot of drivers not calling it.
Invert the boolean, so that the sync will be performed by default and
the shortcut will be enabled only when calling dma_set_mask*().

Reported-by: Steven Price <[email protected]>
Closes: https://lore.kernel.org/lkml/[email protected]
Reported-by: Marek Szyprowski <[email protected]>
Closes: https://lore.kernel.org/lkml/[email protected]
Fixes: f406c8e4b770. ("dma: avoid redundant calls for sync operations")
Signed-off-by: Alexander Lobakin <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>
Tested-by: Steven Price <[email protected]>
Tested-by: Marek Szyprowski <[email protected]>

show more ...

dma: avoid redundant calls for sync operations

Quite often, devices do not need dma_sync operations on x86_64 at least.
Indeed, when dev_is_dma_coherent(dev) is true and
dev_use_swiotlb(dev) is fals

dma: avoid redundant calls for sync operations

Quite often, devices do not need dma_sync operations on x86_64 at least.
Indeed, when dev_is_dma_coherent(dev) is true and
dev_use_swiotlb(dev) is false, iommu_dma_sync_single_for_cpu()
and friends do nothing.

However, indirectly calling them when CONFIG_RETPOLINE=y consumes about
10% of cycles on a cpu receiving packets from softirq at ~100Gbit rate.
Even if/when CONFIG_RETPOLINE is not set, there is a cost of about 3%.

Add dev->need_dma_sync boolean and turn it off during the device
initialization (dma_set_mask()) depending on the setup:
dev_is_dma_coherent() for the direct DMA, !(sync_single_for_device ||
sync_single_for_cpu) or the new dma_map_ops flag, %DMA_F_CAN_SKIP_SYNC,
advertised for non-NULL DMA ops.
Then later, if/when swiotlb is used for the first time, the flag
is reset back to on, from swiotlb_tbl_map_single().

On iavf, the UDP trafficgen with XDP_DROP in skb mode test shows
+3-5% increase for direct DMA.

Suggested-by: Christoph Hellwig <[email protected]> # direct DMA shortcut
Co-developed-by: Eric Dumazet <[email protected]>
Signed-off-by: Eric Dumazet <[email protected]>
Signed-off-by: Alexander Lobakin <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>

show more ...

dma-mapping: Simplify arch_setup_dma_ops()

The dma_base, size and iommu arguments are only used by ARM, and can
now easily be deduced from the device itself, so there's no need to pass
them through

dma-mapping: Simplify arch_setup_dma_ops()

The dma_base, size and iommu arguments are only used by ARM, and can
now easily be deduced from the device itself, so there's no need to pass
them through the callchain as well.

Acked-by: Rob Herring <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Reviewed-by: Michael Kelley <[email protected]> # For Hyper-V
Reviewed-by: Jason Gunthorpe <[email protected]>
Tested-by: Hanjun Guo <[email protected]>
Signed-off-by: Robin Murphy <[email protected]>
Acked-by: Catalin Marinas <[email protected]>
Link: https://lore.kernel.org/r/5291c2326eab405b1aa7693aa964e8d3cb7193de.1713523152.git.robin.murphy@arm.com
Signed-off-by: Joerg Roedel <[email protected]>

show more ...

change alloc_pages name in dma_map_ops to avoid name conflicts

After redefining alloc_pages, all uses of that name are being replaced.
Change the conflicting names to prevent preprocessor from repl

change alloc_pages name in dma_map_ops to avoid name conflicts

After redefining alloc_pages, all uses of that name are being replaced.
Change the conflicting names to prevent preprocessor from replacing them
when it's not intended.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Suren Baghdasaryan <[email protected]>
Tested-by: Kees Cook <[email protected]>
Cc: Alexander Viro <[email protected]>
Cc: Alex Gaynor <[email protected]>
Cc: Alice Ryhl <[email protected]>
Cc: Andreas Hindborg <[email protected]>
Cc: Benno Lossin <[email protected]>
Cc: "Björn Roy Baron" <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Dennis Zhou <[email protected]>
Cc: Gary Guo <[email protected]>
Cc: Kent Overstreet <[email protected]>
Cc: Miguel Ojeda <[email protected]>
Cc: Pasha Tatashin <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Wedson Almeida Filho <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

show more ...

dma-debug: make dma_debug_add_bus take a const pointer

The driver core now can handle a const struct bus_type pointer, and the
dma_debug_add_bus() call just passes on the pointer give to it to the
d

dma-debug: make dma_debug_add_bus take a const pointer

The driver core now can handle a const struct bus_type pointer, and the
dma_debug_add_bus() call just passes on the pointer give to it to the
driver core, so make this pointer const as well to allow everyone to use
read-only struct bus_type pointers going forward.

Cc: Christoph Hellwig <[email protected]>
Cc: Marek Szyprowski <[email protected]>
Cc: Robin Murphy <[email protected]>
Cc: <[email protected]>
Reviewed-by: Robin Murphy <[email protected]>
Link: https://lore.kernel.org/r/2023121941-dejected-nugget-681e@gregkh
Signed-off-by: Greg Kroah-Hartman <[email protected]>

show more ...

iommu: Remove struct iommu_ops *iommu from arch_setup_dma_ops()

This is not being used to pass ops, it is just a way to tell if an
iommu driver was probed. These days this can be detected directly v

iommu: Remove struct iommu_ops *iommu from arch_setup_dma_ops()

This is not being used to pass ops, it is just a way to tell if an
iommu driver was probed. These days this can be detected directly via
device_iommu_mapped(). Call device_iommu_mapped() in the two places that
need to check it and remove the iommu parameter everywhere.

Reviewed-by: Jerry Snitselaar <[email protected]>
Reviewed-by: Lu Baolu <[email protected]>
Reviewed-by: Moritz Fischer <[email protected]>
Acked-by: Christoph Hellwig <[email protected]>
Acked-by: Rob Herring <[email protected]>
Tested-by: Hector Martin <[email protected]>
Signed-off-by: Jason Gunthorpe <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Joerg Roedel <[email protected]>

show more ...

iommu: Retire bus ops

With the rest of the API internals converted, it's time to finally
tackle probe_device and how we bootstrap the per-device ops association
to begin with. This ends up being dis

iommu: Retire bus ops

With the rest of the API internals converted, it's time to finally
tackle probe_device and how we bootstrap the per-device ops association
to begin with. This ends up being disappointingly straightforward, since
fwspec users are already doing it in order to find their of_xlate
callback, and it works out that we can easily do the equivalent for
other drivers too. Then shuffle the remaining awareness of iommu_ops
into the couple of core headers that still need it, and breathe a sigh
of relief.

Ding dong the bus ops are gone!

CC: Rafael J. Wysocki <[email protected]>
Acked-by: Christoph Hellwig <[email protected]>
Acked-by: Greg Kroah-Hartman <[email protected]>
Reviewed-by: Lu Baolu <[email protected]>
Reviewed-by: Jason Gunthorpe <[email protected]>
Reviewed-by: Jerry Snitselaar <[email protected]>
Signed-off-by: Robin Murphy <[email protected]>
Link: https://lore.kernel.org/r/a59011ef65b4b6657cb0b7a388d786b779b61305.1700589539.git.robin.murphy@arm.com
Signed-off-by: Joerg Roedel <[email protected]>

show more ...

dma-contiguous: support per-numa CMA for all architectures

In the commit b7176c261cdb ("dma-contiguous: provide the ability to
reserve per-numa CMA"), Barry adds DMA_PERNUMA_CMA for ARM64.

But this

dma-contiguous: support per-numa CMA for all architectures

In the commit b7176c261cdb ("dma-contiguous: provide the ability to
reserve per-numa CMA"), Barry adds DMA_PERNUMA_CMA for ARM64.

But this feature is architecture independent, so support per-numa CMA
for all architectures, and enable it by default if NUMA.

Signed-off-by: Yajun Deng <[email protected]>
Tested-by: Yicong Yang <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>

show more ...

dma-mapping: move arch_dma_set_mask() declaration to header

This function has a __weak definition and an override that is only used on
freescale powerpc chips. The powerpc definition however does no

dma-mapping: move arch_dma_set_mask() declaration to header

This function has a __weak definition and an override that is only used on
freescale powerpc chips. The powerpc definition however does not see the
declaration that is in a .c file:

arch/powerpc/kernel/dma-mask.c:7:6: error: no previous prototype for 'arch_dma_set_mask' [-Werror=missing-prototypes]

Move it into the linux/dma-map-ops.h header where the other arch_dma_* functions
are declared.

Signed-off-by: Arnd Bergmann <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>

show more ...

dma-mapping: force bouncing if the kmalloc() size is not cache-line-aligned

For direct DMA, if the size is small enough to have originated from a
kmalloc() cache below ARCH_DMA_MINALIGN, check its a

dma-mapping: force bouncing if the kmalloc() size is not cache-line-aligned

For direct DMA, if the size is small enough to have originated from a
kmalloc() cache below ARCH_DMA_MINALIGN, check its alignment against
dma_get_cache_alignment() and bounce if necessary. For larger sizes, it
is the responsibility of the DMA API caller to ensure proper alignment.

At this point, the kmalloc() caches are properly aligned but this will
change in a subsequent patch.

Architectures can opt in by selecting DMA_BOUNCE_UNALIGNED_KMALLOC.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Catalin Marinas <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Reviewed-by: Robin Murphy <[email protected]>
Tested-by: Isaac J. Manjarres <[email protected]>
Cc: Alasdair Kergon <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Herbert Xu <[email protected]>
Cc: Jerry Snitselaar <[email protected]>
Cc: Joerg Roedel <[email protected]>
Cc: Jonathan Cameron <[email protected]>
Cc: Jonathan Cameron <[email protected]>
Cc: Lars-Peter Clausen <[email protected]>
Cc: Logan Gunthorpe <[email protected]>
Cc: Marc Zyngier <[email protected]>
Cc: Mark Brown <[email protected]>
Cc: Mike Snitzer <[email protected]>
Cc: "Rafael J. Wysocki" <[email protected]>
Cc: Saravana Kannan <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Will Deacon <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

show more ...

dma-mapping: provide a fallback dma_default_coherent

dma_default_coherent was decleared unconditionally at kernel/dma/mapping.c
but only decleared when any of non-coherent options is enabled in
dma-

dma-mapping: provide a fallback dma_default_coherent

dma_default_coherent was decleared unconditionally at kernel/dma/mapping.c
but only decleared when any of non-coherent options is enabled in
dma-map-ops.h.

Guard the declaration in mapping.c with non-coherent options and provide
a fallback definition.

Signed-off-by: Jiaxun Yang <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>

show more ...

dma-mapping: no need to pass a bus_type into get_arch_dma_ops()

The get_arch_dma_ops() arch-specific function never does anything with
the struct bus_type that is passed into it, so remove it entire

dma-mapping: no need to pass a bus_type into get_arch_dma_ops()

The get_arch_dma_ops() arch-specific function never does anything with
the struct bus_type that is passed into it, so remove it entirely as it
is not needed.

Cc: Richard Henderson <[email protected]>
Cc: Ivan Kokshaysky <[email protected]>
Cc: Matt Turner <[email protected]>
Cc: Thomas Bogendoerfer <[email protected]>
Cc: "James E.J. Bottomley" <[email protected]>
Cc: Helge Deller <[email protected]>
Cc: "David S. Miller" <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: [email protected]
Cc: "H. Peter Anvin" <[email protected]>
Cc: Marek Szyprowski <[email protected]>
Cc: Robin Murphy <[email protected]>
Cc: Konrad Rzeszutek Wilk <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Acked-by: Christoph Hellwig <[email protected]>
Reviewed-by: Arnd Bergmann <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

show more ...

dma-mapping: add flags to dma_map_ops to indicate PCI P2PDMA support

Add a flags member to the dma_map_ops structure with one flag to
indicate support for PCI P2PDMA.

Also, add a helper to check if

dma-mapping: add flags to dma_map_ops to indicate PCI P2PDMA support

Add a flags member to the dma_map_ops structure with one flag to
indicate support for PCI P2PDMA.

Also, add a helper to check if a device supports PCI P2PDMA.

Signed-off-by: Logan Gunthorpe <[email protected]>
Reviewed-by: Jason Gunthorpe <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>

show more ...

PCI/P2PDMA: Introduce helpers for dma_map_sg implementations

Add pci_p2pdma_map_segment() as a helper for dma_map_sg()
implementations. It takes an scatterlist segment that must point to a
pci_p2pdm

PCI/P2PDMA: Introduce helpers for dma_map_sg implementations

Add pci_p2pdma_map_segment() as a helper for dma_map_sg()
implementations. It takes an scatterlist segment that must point to a
pci_p2pdma struct page and will map it if the mapping requires a bus
address.

The return value indicates whether the mapping required a bus address
or whether the caller still needs to map the segment normally. If the
segment should not be mapped, -EREMOTEIO is returned.

This helper uses a state structure to track the changes to the
pgmap across calls and avoid needing to lookup into the xarray for
every page.

The prototype for the helper is added to dma-map-ops.h as it is only
useful to dma map implementations and don't need to pollute the public
pci-p2pdma header.

Signed-off-by: Logan Gunthorpe <[email protected]>
Acked-by: Bjorn Helgaas <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>

show more ...

dma-mapping: add dma_opt_mapping_size()

Streaming DMA mapping involving an IOMMU may be much slower for larger
total mapping size. This is because every IOMMU DMA mapping requires an
IOVA to be allo

dma-mapping: add dma_opt_mapping_size()

Streaming DMA mapping involving an IOMMU may be much slower for larger
total mapping size. This is because every IOMMU DMA mapping requires an
IOVA to be allocated and freed. IOVA sizes above a certain limit are not
cached, which can have a big impact on DMA mapping performance.

Provide an API for device drivers to know this "optimal" limit, such that
they may try to produce mapping which don't exceed it.

Signed-off-by: John Garry <[email protected]>
Reviewed-by: Damien Le Moal <[email protected]>
Acked-by: Martin K. Petersen <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>

show more ...

dma-mapping: Fix build error unused-value

If CONFIG_DMA_DECLARE_COHERENT is not set,
make ARCH=x86_64 CROSS_COMPILE=x86_64-linux-gnu- will be failed, like this:

drivers/remoteproc/remoteproc_core.c

dma-mapping: Fix build error unused-value

If CONFIG_DMA_DECLARE_COHERENT is not set,
make ARCH=x86_64 CROSS_COMPILE=x86_64-linux-gnu- will be failed, like this:

drivers/remoteproc/remoteproc_core.c: In function ‘rproc_rvdev_release’:
./include/linux/dma-map-ops.h:182:42: error: statement with no effect [-Werror=unused-value]
#define dma_release_coherent_memory(dev) (0)
^
drivers/remoteproc/remoteproc_core.c:464:2: note: in expansion of macro ‘dma_release_coherent_memory’
dma_release_coherent_memory(dev);
^~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors

The return type of function dma_release_coherent_memory in CONFIG_DMA_DECLARE_COHERENT area is void, so in !CONFIG_DMA_DECLARE_COHERENT area it should neither return any value nor be defined as zero.

Reported-by: Hulk Robot <[email protected]>
Fixes: e61c451476e6 ("dma-mapping: Add dma_release_coherent_memory to DMA API")
Signed-off-by: Ren Zhijie <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Mathieu Poirier <[email protected]>

show more ...

dma-mapping: Add dma_release_coherent_memory to DMA API

Add dma_release_coherent_memory to DMA API to allow dma
user call it to release dev->dma_mem when the device is
removed.

Signed-off-by: Mark-

dma-mapping: Add dma_release_coherent_memory to DMA API

Add dma_release_coherent_memory to DMA API to allow dma
user call it to release dev->dma_mem when the device is
removed.

Signed-off-by: Mark-PK Tsai <[email protected]>
Acked-by: Christoph Hellwig <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Mathieu Poirier <[email protected]>

show more ...

dma-mapping: make the global coherent pool conditional

Only build the code to support the global coherent pool if support for
it is enabled.

Signed-off-by: Christoph Hellwig <[email protected]>
Tested-by:

dma-mapping: make the global coherent pool conditional

Only build the code to support the global coherent pool if support for
it is enabled.

Signed-off-by: Christoph Hellwig <[email protected]>
Tested-by: Dillon Min <[email protected]>

show more ...

dma-mapping: add a dma_init_global_coherent helper

Add a new helper to initialize the global coherent pool. This both
cleans up the existing initialization which indirects through the
reserved_mem_

dma-mapping: add a dma_init_global_coherent helper

Add a new helper to initialize the global coherent pool. This both
cleans up the existing initialization which indirects through the
reserved_mem_ops that are normally only used for struct device, and
also allows using the global pool for non-devicetree architectures.

Signed-off-by: Christoph Hellwig <[email protected]>
Tested-by: Dillon Min <[email protected]>

show more ...

dma-mapping: allow map_sg() ops to return negative error codes

Allow dma_map_sgtable() to pass errors from the map_sg() ops. This
will be required for returning appropriate error codes when mapping

dma-mapping: allow map_sg() ops to return negative error codes

Allow dma_map_sgtable() to pass errors from the map_sg() ops. This
will be required for returning appropriate error codes when mapping
P2PDMA memory.

Introduce __dma_map_sg_attrs() which will return the raw error code
from the map_sg operation (whether it be negative or zero). Then add a
dma_map_sg_attrs() wrapper to convert any negative errors to zero to
satisfy the existing calling convention.

dma_map_sgtable() defines three error codes that .map_sg implementations
are allowed to return: -EINVAL, -ENOMEM and -EIO. The latter of which
is a generic return for cases that are passing DMA_MAPPING_ERROR
through.

dma_map_sgtable() will convert a zero error return for old map_sg() ops
into a -EIO return and return any negative errors as reported.

This allows map_sg implementations to start returning multiple
negative error codes. Legacy map_sg implementations can continue
to return zero until they are all converted.

Signed-off-by: Logan Gunthorpe <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>

show more ...

dma-mapping: add a dma_alloc_noncontiguous API

Add a new API that returns a potentiall virtually non-contigous sg_table
and a DMA address. This API is only properly implemented for dma-iommu
and wi

dma-mapping: add a dma_alloc_noncontiguous API

Add a new API that returns a potentiall virtually non-contigous sg_table
and a DMA address. This API is only properly implemented for dma-iommu
and will simply return a contigious chunk as a fallback.

The intent is that drivers can use this API if either:

- no kernel mapping or only temporary kernel mappings are required.
That is as a better replacement for DMA_ATTR_NO_KERNEL_MAPPING
- a kernel mapping is required for cached and DMA mapped pages, but
the driver also needs the pages to e.g. map them to userspace.
In that sense it is a replacement for some aspects of the recently
removed and never fully implemented DMA_ATTR_NON_CONSISTENT

Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Tomasz Figa <[email protected]>
Tested-by: Ricardo Ribalda <[email protected]>

show more ...