linux/arch/Kconfig
Johannes Berg 58340a07c1 introduce HAVE_EFFICIENT_UNALIGNED_ACCESS Kconfig symbol
In many cases, especially in networking, it can be beneficial to know at
compile time whether the architecture can do unaligned accesses efficiently.
This patch introduces a new Kconfig symbol

	HAVE_EFFICIENT_UNALIGNED_ACCESS

for that purpose and adds it to the powerpc and x86 architectures.  Also add
some documentation about alignment and networking, and especially one intended
use of this symbol.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Ingo Molnar <mingo@elte.hu> [x86 architecture part]
Cc: <linux-arch@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-07-25 10:53:27 -07:00

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#
# General architecture dependent options
#
config OPROFILE
tristate "OProfile system profiling (EXPERIMENTAL)"
depends on PROFILING
depends on HAVE_OPROFILE
help
OProfile is a profiling system capable of profiling the
whole system, include the kernel, kernel modules, libraries,
and applications.
If unsure, say N.
config HAVE_OPROFILE
def_bool n
config KPROBES
bool "Kprobes"
depends on KALLSYMS && MODULES
depends on HAVE_KPROBES
help
Kprobes allows you to trap at almost any kernel address and
execute a callback function. register_kprobe() establishes
a probepoint and specifies the callback. Kprobes is useful
for kernel debugging, non-intrusive instrumentation and testing.
If in doubt, say "N".
config HAVE_EFFICIENT_UNALIGNED_ACCESS
def_bool n
help
Some architectures are unable to perform unaligned accesses
without the use of get_unaligned/put_unaligned. Others are
unable to perform such accesses efficiently (e.g. trap on
unaligned access and require fixing it up in the exception
handler.)
This symbol should be selected by an architecture if it can
perform unaligned accesses efficiently to allow different
code paths to be selected for these cases. Some network
drivers, for example, could opt to not fix up alignment
problems with received packets if doing so would not help
much.
See Documentation/unaligned-memory-access.txt for more
information on the topic of unaligned memory accesses.
config KRETPROBES
def_bool y
depends on KPROBES && HAVE_KRETPROBES
config HAVE_IOREMAP_PROT
def_bool n
config HAVE_KPROBES
def_bool n
config HAVE_KRETPROBES
def_bool n
config HAVE_DMA_ATTRS
def_bool n
config USE_GENERIC_SMP_HELPERS
def_bool n
config HAVE_CLK
def_bool n
help
The <linux/clk.h> calls support software clock gating and
thus are a key power management tool on many systems.