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    Subject[PATCHv4 2/4] ARM: Allow machines to override __delay()
    Date
    Some machines want to implement their own __delay() routine based
    on fixed rate timers. Expose functionality to set the __delay()
    routine at runtime. This should allow two machines with different
    __delay() routines to happily co-exist within the same kernel
    with minimal overhead.

    Russell expressed concern that using a timer based __delay()
    would cause problems when an iomapped device isn't mapped in
    prior to a delay call being made (see
    http://article.gmane.org/gmane.linux.ports.arm.kernel/78543 for
    more info). We can sidestep that issue with this approach since
    the __delay() routine _should_ only be pointed to a timer based
    delay once the timer has been properly mapped. Up until that
    point __delay() and udelay() will use delay_loop() which is
    always safe to call.

    This patch is inspired by x86's delay.c

    Reviewed-by: Saravana Kannan <skannan@codeaurora.org>
    Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
    ---

    Changed to inline set_delay_fn()

    arch/arm/include/asm/delay.h | 7 +++++++
    arch/arm/lib/delay.c | 14 +++++++++++---
    2 files changed, 18 insertions(+), 3 deletions(-)

    diff --git a/arch/arm/include/asm/delay.h b/arch/arm/include/asm/delay.h
    index ccc5ed5..82ef82a 100644
    --- a/arch/arm/include/asm/delay.h
    +++ b/arch/arm/include/asm/delay.h
    @@ -40,5 +40,12 @@ extern void __const_udelay(unsigned long);
    __const_udelay((n) * ((2199023U*HZ)>>11))) : \
    __udelay(n))

    +extern void (*delay_fn)(unsigned long);
    +
    +static inline void set_delay_fn(void (*fn)(unsigned long))
    +{
    + delay_fn = fn;
    +}
    +
    #endif /* defined(_ARM_DELAY_H) */

    diff --git a/arch/arm/lib/delay.c b/arch/arm/lib/delay.c
    index f92aca0..7468bc6 100644
    --- a/arch/arm/lib/delay.c
    +++ b/arch/arm/lib/delay.c
    @@ -11,11 +11,9 @@
    #include <linux/delay.h>

    /*
    - * loops = usecs * HZ * loops_per_jiffy / 1000000
    - *
    * Oh, if only we had a cycle counter...
    */
    -void __delay(unsigned long loops)
    +static void delay_loop(unsigned long loops)
    {
    asm volatile(
    "1: subs %0, %0, #1 \n"
    @@ -24,6 +22,16 @@ void __delay(unsigned long loops)
    : "r" (loops)
    );
    }
    +
    +void (*delay_fn)(unsigned long) = delay_loop;
    +
    +/*
    + * loops = usecs * HZ * loops_per_jiffy / 1000000
    + */
    +void __delay(unsigned long loops)
    +{
    + delay_fn(loops);
    +}
    EXPORT_SYMBOL(__delay);

    /*
    --
    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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