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authorMauro Carvalho Chehab <mchehab+samsung@kernel.org>2019-04-14 21:51:10 +0300
committerMauro Carvalho Chehab <mchehab+samsung@kernel.org>2019-07-15 15:20:24 +0300
commitdc7a12bdfccd94c31f79e294f16f7549bd411b49 (patch)
tree81da5ca148347b94c4539234f50d4bca6465e2f8 /Documentation/arm/swp_emulation.rst
parent0d07cf5e53a21e35289adc3ab99b6804ff0c3833 (diff)
downloadlinux-dc7a12bdfccd94c31f79e294f16f7549bd411b49.tar.xz
docs: arm: convert docs to ReST and rename to *.rst
Converts ARM the text files to ReST, preparing them to be an architecture book. The conversion is actually: - add blank lines and identation in order to identify paragraphs; - fix tables markups; - add some lists markups; - mark literal blocks; - adjust title markups. At its new index.rst, let's add a :orphan: while this is not linked to the main index.rst file, in order to avoid build warnings. Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> Reviewed-by Corentin Labbe <clabbe.montjoie@gmail.com> # For sun4i-ss
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+Software emulation of deprecated SWP instruction (CONFIG_SWP_EMULATE)
+---------------------------------------------------------------------
+
+ARMv6 architecture deprecates use of the SWP/SWPB instructions, and recommeds
+moving to the load-locked/store-conditional instructions LDREX and STREX.
+
+ARMv7 multiprocessing extensions introduce the ability to disable these
+instructions, triggering an undefined instruction exception when executed.
+Trapped instructions are emulated using an LDREX/STREX or LDREXB/STREXB
+sequence. If a memory access fault (an abort) occurs, a segmentation fault is
+signalled to the triggering process.
+
+/proc/cpu/swp_emulation holds some statistics/information, including the PID of
+the last process to trigger the emulation to be invocated. For example::
+
+ Emulated SWP: 12
+ Emulated SWPB: 0
+ Aborted SWP{B}: 1
+ Last process: 314
+
+
+NOTE:
+ when accessing uncached shared regions, LDREX/STREX rely on an external
+ transaction monitoring block called a global monitor to maintain update
+ atomicity. If your system does not implement a global monitor, this option can
+ cause programs that perform SWP operations to uncached memory to deadlock, as
+ the STREX operation will always fail.