summaryrefslogtreecommitdiff
path: root/Documentation
diff options
context:
space:
mode:
authorLinus Torvalds <torvalds@linux-foundation.org>2011-01-06 16:50:35 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2011-01-06 16:50:35 -0800
commit3c0cb7c31c206aaedb967e44b98442bbeb17a6c4 (patch)
tree3ecba45d7ffae4fba4a5aafaef4af5b0b1105bde /Documentation
parentf70f5b9dc74ca7d0a64c4ead3fb28da09dc1b234 (diff)
parent404a02cbd2ae8bf256a2fa1169bdfe86bb5ebb34 (diff)
Merge branch 'devel' of master.kernel.org:/home/rmk/linux-2.6-arm
* 'devel' of master.kernel.org:/home/rmk/linux-2.6-arm: (416 commits) ARM: DMA: add support for DMA debugging ARM: PL011: add DMA burst threshold support for ST variants ARM: PL011: Add support for transmit DMA ARM: PL011: Ensure IRQs are disabled in UART interrupt handler ARM: PL011: Separate hardware FIFO size from TTY FIFO size ARM: PL011: Allow better handling of vendor data ARM: PL011: Ensure error flags are clear at startup ARM: PL011: include revision number in boot-time port printk ARM: vexpress: add sched_clock() for Versatile Express ARM i.MX53: Make MX53 EVK bootable ARM i.MX53: Some bug fix about MX53 MSL code ARM: 6607/1: sa1100: Update platform device registration ARM: 6606/1: sa1100: Fix platform device registration ARM i.MX51: rename IPU irqs ARM i.MX51: Add ipu clock support ARM: imx/mx27_3ds: Add PMIC support ARM: DMA: Replace page_to_dma()/dma_to_page() with pfn_to_dma()/dma_to_pfn() mx51: fix usb clock support MX51: Add support for usb host 2 arch/arm/plat-mxc/ehci.c: fix errors/typos ...
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/arm/00-INDEX2
-rw-r--r--Documentation/arm/swp_emulation27
2 files changed, 29 insertions, 0 deletions
diff --git a/Documentation/arm/00-INDEX b/Documentation/arm/00-INDEX
index ecf7d04bca26..91c24a1e8a9e 100644
--- a/Documentation/arm/00-INDEX
+++ b/Documentation/arm/00-INDEX
@@ -34,3 +34,5 @@ memory.txt
- description of the virtual memory layout
nwfpe/
- NWFPE floating point emulator documentation
+swp_emulation
+ - SWP/SWPB emulation handler/logging description
diff --git a/Documentation/arm/swp_emulation b/Documentation/arm/swp_emulation
new file mode 100644
index 000000000000..af903d22fd93
--- /dev/null
+++ b/Documentation/arm/swp_emulation
@@ -0,0 +1,27 @@
+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.
+