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      x86: Remove the ancient and deprecated disable_hlt() and enable_hlt() facility · f6365201
      Len Brown 提交于
      The X86_32-only disable_hlt/enable_hlt mechanism was used by the
      32-bit floppy driver. Its effect was to replace the use of the
      HLT instruction inside default_idle() with cpu_relax() - essentially
      it turned off the use of HLT.
      
      This workaround was commented in the code as:
      
       "disable hlt during certain critical i/o operations"
      
       "This halt magic was a workaround for ancient floppy DMA
        wreckage. It should be safe to remove."
      
      H. Peter Anvin additionally adds:
      
       "To the best of my knowledge, no-hlt only existed because of
        flaky power distributions on 386/486 systems which were sold to
        run DOS.  Since DOS did no power management of any kind,
        including HLT, the power draw was fairly uniform; when exposed
        to the much hhigher noise levels you got when Linux used HLT
        caused some of these systems to fail.
      
        They were by far in the minority even back then."
      
      Alan Cox further says:
      
       "Also for the Cyrix 5510 which tended to go castors up if a HLT
        occurred during a DMA cycle and on a few other boxes HLT during
        DMA tended to go astray.
      
        Do we care ? I doubt it. The 5510 was pretty obscure, the 5520
        fixed it, the 5530 is probably the oldest still in any kind of
        use."
      
      So, let's finally drop this.
      Signed-off-by: NLen Brown <len.brown@intel.com>
      Signed-off-by: NJosh Boyer <jwboyer@redhat.com>
      Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
      Acked-by: N"H. Peter Anvin" <hpa@zytor.com>
      Acked-by: NAlan Cox <alan@lxorguk.ukuu.org.uk>
      Cc: Stephen Hemminger <shemminger@vyatta.com
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: <stable@kernel.org>
      Link: http://lkml.kernel.org/n/tip-3rhk9bzf0x9rljkv488tloib@git.kernel.org
      [ If anyone cares then alternative instruction patching could be
        used to replace HLT with a one-byte NOP instruction. Much simpler. ]
      Signed-off-by: NIngo Molnar <mingo@kernel.org>
      f6365201