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Merge branch 'devel' of master.kernel.org:/home/rmk/linux-2.6-arm
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* '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
  ...
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torvalds committed Jan 7, 2011
2 parents f70f5b9 + 404a02c commit 3c0cb7c
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2 changes: 2 additions & 0 deletions Documentation/arm/00-INDEX
Original file line number Diff line number Diff line change
Expand Up @@ -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
27 changes: 27 additions & 0 deletions Documentation/arm/swp_emulation
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@@ -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.

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