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    SubjectRe: [PATCH] ARM: cache-v7: Disable preemption when reading CCSIDR
    On 02/02/12 16:36, Russell King - ARM Linux wrote:
    > On Thu, Feb 02, 2012 at 03:36:49PM -0800, Stephen Boyd wrote:
    >> On 02/02/12 13:38, Nicolas Pitre wrote:
    >>> On Thu, 2 Feb 2012, Russell King - ARM Linux wrote
    >>>> On Thu, Feb 02, 2012 at 11:24:46AM -0800, Stephen Boyd wrote:
    >>>>> Should we move get_thread_info into assembler.h? It seems odd
    >>>>> to include entry-header.S but I saw that vfp was doing the same.
    >>>> Probably yes, and probably also have preempt_disable and preempt_enable
    >>>> assembler macros. That's going to get rather icky if we have to
    >>>> explicitly call the scheduler though (to solve (1)).
    >>> What about a pair of helpers written in C instead?
    >>> v7_flush_dcache_all() could be renamed, and a wrapper function called
    >>> v7_flush_dcache_all() would call the preemption disable helper, call the
    >>> former v7_flush_dcache_all code, then call the preemption enable helper.
    >>> Then __v7_setup() could still call the core cache flush code without
    >>> issues.
    >> I tried to put the preemption disable/enable right around the place
    >> where it was needed. With this approach we would disable preemption
    >> during the entire cache flush. I'm not sure if we want to make this
    >> function worse for performance, do we? It certainly sounds easier than
    >> writing all the preempt macros in assembly though.
    > Err, why do you think it's a big task?
    > preempt disable is a case of incrementing the thread preempt count, while
    > preempt enable is a case of decrementing it, testing for zero, if zero,
    > then checking whether TIF_NEED_RESCHED is set and calling a function.
    > If that's too much, then the simple method in assembly to quickly disable
    > preemption over a very few set of instructions is using mrs/msr and cpsid i.
    > That'll be far cheaper than fiddling about with preempt counters or
    > messing about with veneers in C code.

    I'll try the macros. So far it isn't bad, just the __v7_setup to resolve.

    Sent by an employee of the Qualcomm Innovation Center, Inc.
    The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

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