The following primitives are defined in linux/bitfield.h:
* u32 le32_get_bits(__le32 val, u32 field) extracts the contents of the
bitfield specified by @field in little-endian 32bit object @val and
converts it to host-endian.
* void le32p_replace_bits(__le32 *p, u32 v, u32 field) replaces
the contents of the bitfield specified by @field in little-endian
32bit object pointed to by @p with the value of @v. New value is
given in host-endian and stored as little-endian.
* __le32 le32_replace_bits(__le32 old, u32 v, u32 field) is equivalent to
({__le32 tmp = old; le32p_replace_bits(&tmp, v, field); tmp;})
In other words, instead of modifying an object in memory, it takes
the initial value and returns the modified one.
* __le32 le32_encode_bits(u32 v, u32 field) is equivalent to
le32_replace_bits(0, v, field). In other words, it returns a little-endian
32bit object with the bitfield specified by @field containing the
value of @v and all bits outside that bitfield being zero.
Such set of helpers is defined for each of little-, big- and host-endian
types; e.g. u64_get_bits(val, field) will return the contents of the bitfield
specified by @field in host-endian 64bit object @val, etc. Of course, for
host-endian no conversion is involved.
Fields to access are specified as GENMASK() values - an N-bit field
starting at bit #M is encoded as GENMASK(M + N - 1, M). Note that
bit numbers refer to endianness of the object we are working with -
e.g. GENMASK(11, 0) in __be16 refers to the second byte and the lower
4 bits of the first byte. In __le16 it would refer to the first byte
and the lower 4 bits of the second byte, etc.
Field specification must be a constant; __builtin_constant_p() doesn't
have to be true for it, but compiler must be able to evaluate it at
build time. If it cannot or if the value does not encode any bitfield,
the build will fail.
If the value being stored in a bitfield is a constant that does not fit
into that bitfield, a warning will be generated at compile time.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Since commit bc6245e5ef ("bug: split BUILD_BUG stuff out into
<linux/build_bug.h>"), #include <linux/build_bug.h> is better to pull
minimal headers needed for BUILG_BUG() family.
Link: http://lkml.kernel.org/r/1505700775-19826-1-git-send-email-yamada.masahiro@socionext.com
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Cc: Dinan Gunawardena <dinan.gunawardena@netronome.com>
Cc: Kalle Valo <kvalo@codeaurora.org>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
I do not see anything that restricts this macro to 32 bit width.
Link: http://lkml.kernel.org/r/1505921975-23379-1-git-send-email-yamada.masahiro@socionext.com
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Add a helper for checking at runtime that a value will fit inside
a specified field/mask.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Common approach to accessing register fields is to define
structures or sets of macros containing mask and shift pair.
Operations on the register are then performed as follows:
field = (reg >> shift) & mask;
reg &= ~(mask << shift);
reg |= (field & mask) << shift;
Defining shift and mask separately is tedious. Ivo van Doorn
came up with an idea of computing them at compilation time
based on a single shifted mask (later refined by Felix) which
can be used like this:
#define REG_FIELD 0x000ff000
field = FIELD_GET(REG_FIELD, reg);
reg &= ~REG_FIELD;
reg |= FIELD_PREP(REG_FIELD, field);
FIELD_{GET,PREP} macros take care of finding out what the
appropriate shift is based on compilation time ffs operation.
GENMASK can be used to define registers (which is usually
less error-prone and easier to match with datasheets).
This approach is the most convenient I've seen so to limit code
multiplication let's move the macros to a global header file.
Attempts to use static inlines instead of macros failed due
to false positive triggering of BUILD_BUG_ON()s, especially with
GCC < 6.0.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Dinan Gunawardena <dinan.gunawardena@netronome.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
