mirror of
https://mirrors.bfsu.edu.cn/git/linux.git
synced 2024-11-11 21:38:32 +08:00
e66f6e0954
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
92 lines
3.2 KiB
ReStructuredText
92 lines
3.2 KiB
ReStructuredText
========================
|
|
The io_mapping functions
|
|
========================
|
|
|
|
API
|
|
===
|
|
|
|
The io_mapping functions in linux/io-mapping.h provide an abstraction for
|
|
efficiently mapping small regions of an I/O device to the CPU. The initial
|
|
usage is to support the large graphics aperture on 32-bit processors where
|
|
ioremap_wc cannot be used to statically map the entire aperture to the CPU
|
|
as it would consume too much of the kernel address space.
|
|
|
|
A mapping object is created during driver initialization using::
|
|
|
|
struct io_mapping *io_mapping_create_wc(unsigned long base,
|
|
unsigned long size)
|
|
|
|
'base' is the bus address of the region to be made
|
|
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
|
|
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 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.
|
|
|
|
This _wc variant returns a write-combining map to the page and may only be
|
|
used with mappings created by io_mapping_create_wc()
|
|
|
|
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_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 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/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)
|
|
|
|
Use for pages mapped with io_mapping_map_wc().
|
|
|
|
At driver close time, the io_mapping object must be freed::
|
|
|
|
void io_mapping_free(struct io_mapping *mapping)
|