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io-mapping: Provide iomap_local variant

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Similar to kmap local provide a iomap local variant which only disables
migration, but neither disables pagefaults nor preemption.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20201118204007.561220818@linutronix.de
This commit is contained in:
Thomas Gleixner 2020-11-18 20:48:45 +01:00
parent f3ba3c710a
commit e66f6e0954
2 changed files with 73 additions and 31 deletions
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74
Documentation/driver-api/io-mapping.rst
View file

@ -20,55 +20,71 @@ A mapping object is created during driver initialization using::
mappable, while 'size' indicates how large a mapping region to
enable. Both are in bytes.
This _wc variant provides a mapping which may only be used
with the io_mapping_map_atomic_wc or io_mapping_map_wc.
This _wc variant provides a mapping which may only be used with
io_mapping_map_atomic_wc(), io_mapping_map_local_wc() or
io_mapping_map_wc().
With this mapping object, individual pages can be mapped either atomically
or not, depending on the necessary scheduling environment. Of course, atomic
maps are more efficient::
With this mapping object, individual pages can be mapped either temporarily
or long term, depending on the requirements. Of course, temporary maps are
more efficient. They come in two flavours::
void *io_mapping_map_local_wc(struct io_mapping *mapping,
unsigned long offset)
void *io_mapping_map_atomic_wc(struct io_mapping *mapping,
unsigned long offset)
'offset' is the offset within the defined mapping region.
Accessing addresses beyond the region specified in the
creation function yields undefined results. Using an offset
which is not page aligned yields an undefined result. The
return value points to a single page in CPU address space.
'offset' is the offset within the defined mapping region. Accessing
addresses beyond the region specified in the creation function yields
undefined results. Using an offset which is not page aligned yields an
undefined result. The return value points to a single page in CPU address
space.
This _wc variant returns a write-combining map to the
page and may only be used with mappings created by
io_mapping_create_wc
This _wc variant returns a write-combining map to the page and may only be
used with mappings created by io_mapping_create_wc()
Note that the task may not sleep while holding this page
mapped.
Temporary mappings are only valid in the context of the caller. The mapping
is not guaranteed to be globaly visible.
::
io_mapping_map_local_wc() has a side effect on X86 32bit as it disables
migration to make the mapping code work. No caller can rely on this side
effect.
io_mapping_map_atomic_wc() has the side effect of disabling preemption and
pagefaults. Don't use in new code. Use io_mapping_map_local_wc() instead.
Nested mappings need to be undone in reverse order because the mapping
code uses a stack for keeping track of them::
addr1 = io_mapping_map_local_wc(map1, offset1);
addr2 = io_mapping_map_local_wc(map2, offset2);
...
io_mapping_unmap_local(addr2);
io_mapping_unmap_local(addr1);
The mappings are released with::
void io_mapping_unmap_local(void *vaddr)
void io_mapping_unmap_atomic(void *vaddr)
'vaddr' must be the value returned by the last
io_mapping_map_atomic_wc call. This unmaps the specified
page and allows the task to sleep once again.
'vaddr' must be the value returned by the last io_mapping_map_local_wc() or
io_mapping_map_atomic_wc() call. This unmaps the specified mapping and
undoes the side effects of the mapping functions.
If you need to sleep while holding the lock, you can use the non-atomic
variant, although they may be significantly slower.
::
If you need to sleep while holding a mapping, you can use the regular
variant, although this may be significantly slower::
void *io_mapping_map_wc(struct io_mapping *mapping,
unsigned long offset)
This works like io_mapping_map_atomic_wc except it allows
the task to sleep while holding the page mapped.
This works like io_mapping_map_atomic/local_wc() except it has no side
effects and the pointer is globaly visible.
::
The mappings are released with::
void io_mapping_unmap(void *vaddr)
This works like io_mapping_unmap_atomic, except it is used
for pages mapped with io_mapping_map_wc.
Use for pages mapped with io_mapping_map_wc().
At driver close time, the io_mapping object must be freed::

30
include/linux/io-mapping.h
View file

@ -82,6 +82,21 @@ io_mapping_unmap_atomic(void __iomem *vaddr)
preempt_enable();
}
static inline void __iomem *
io_mapping_map_local_wc(struct io_mapping *mapping, unsigned long offset)
{
resource_size_t phys_addr;
BUG_ON(offset >= mapping->size);
phys_addr = mapping->base + offset;
return __iomap_local_pfn_prot(PHYS_PFN(phys_addr), mapping->prot);
}
static inline void io_mapping_unmap_local(void __iomem *vaddr)
{
kunmap_local_indexed((void __force *)vaddr);
}
static inline void __iomem *
io_mapping_map_wc(struct io_mapping *mapping,
unsigned long offset,
@ -101,7 +116,7 @@ io_mapping_unmap(void __iomem *vaddr)
iounmap(vaddr);
}
#else
#else /* HAVE_ATOMIC_IOMAP */
#include <linux/uaccess.h>
@ -166,7 +181,18 @@ io_mapping_unmap_atomic(void __iomem *vaddr)
preempt_enable();
}
#endif /* HAVE_ATOMIC_IOMAP */
static inline void __iomem *
io_mapping_map_local_wc(struct io_mapping *mapping, unsigned long offset)
{
return io_mapping_map_wc(mapping, offset, PAGE_SIZE);
}
static inline void io_mapping_unmap_local(void __iomem *vaddr)
{
io_mapping_unmap(vaddr);
}
#endif /* !HAVE_ATOMIC_IOMAP */
static inline struct io_mapping *
io_mapping_create_wc(resource_size_t base,