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    Subject[tip:x86/timers] x86/hpet: Add function to select a /dev/hpet channel
    Commit-ID:  af5a1dadf3fcf673906af1a1129b2b7528494ee5
    Gitweb: https://git.kernel.org/tip/af5a1dadf3fcf673906af1a1129b2b7528494ee5
    Author: Thomas Gleixner <tglx@linutronix.de>
    AuthorDate: Sun, 23 Jun 2019 15:24:01 +0200
    Committer: Thomas Gleixner <tglx@linutronix.de>
    CommitDate: Fri, 28 Jun 2019 00:57:23 +0200

    x86/hpet: Add function to select a /dev/hpet channel

    If CONFIG_HPET=y is enabled the x86 specific HPET code should reserve at
    least one channel for the /dev/hpet character device, so that not all
    channels are absorbed for per CPU clockevent devices.

    Create a function to assign HPET_MODE_DEVICE so the rework of the
    clockevents allocation code can utilize the mode information instead of
    reducing the number of evaluated channels by #ifdef hackery.

    The function is not yet used, but provided as a separate patch for ease of
    review. It will be used when the rework of the clockevent selection takes
    place.

    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Reviewed-by: Ingo Molnar <mingo@kernel.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
    Cc: Ashok Raj <ashok.raj@intel.com>
    Cc: Andi Kleen <andi.kleen@intel.com>
    Cc: Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>
    Cc: Stephane Eranian <eranian@google.com>
    Cc: Ravi Shankar <ravi.v.shankar@intel.com>
    Link: https://lkml.kernel.org/r/20190623132436.002758910@linutronix.de

    ---
    arch/x86/kernel/hpet.c | 17 +++++++++++++++++
    1 file changed, 17 insertions(+)

    diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
    index 3a8ec363d569..640ff75cc523 100644
    --- a/arch/x86/kernel/hpet.c
    +++ b/arch/x86/kernel/hpet.c
    @@ -228,8 +228,25 @@ static void __init hpet_reserve_platform_timers(void)
    hpet_alloc(&hd);

    }
    +
    +static void __init hpet_select_device_channel(void)
    +{
    + int i;
    +
    + for (i = 0; i < hpet_base.nr_channels; i++) {
    + struct hpet_channel *hc = hpet_base.channels + i;
    +
    + /* Associate the first unused channel to /dev/hpet */
    + if (hc->mode == HPET_MODE_UNUSED) {
    + hc->mode = HPET_MODE_DEVICE;
    + return;
    + }
    + }
    +}
    +
    #else
    static inline void hpet_reserve_platform_timers(void) { }
    +static inline void hpet_select_device_channel(void) {}
    #endif

    /* Common HPET functions */
    \
     
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