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    Subject[PATCH 3.13.y-ckt 080/143] cpufreq: speedstep-smi: enable interrupts when waiting
    Date
    3.13.11-ckt18 -stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Mikulas Patocka <mpatocka@redhat.com>

    commit d4d4eda23794c701442e55129dd4f8f2fefd5e4d upstream.

    On Dell Latitude C600 laptop with Pentium 3 850MHz processor, the
    speedstep-smi driver sometimes loads and sometimes doesn't load with
    "change to state X failed" message.

    The hardware sometimes refuses to change frequency and in this case, we
    need to retry later. I found out that we need to enable interrupts while
    waiting. When we enable interrupts, the hardware blockage that prevents
    frequency transition resolves and the transition is possible. With
    disabled interrupts, the blockage doesn't resolve (no matter how long do
    we wait). The exact reasons for this hardware behavior are unknown.

    This patch enables interrupts in the function speedstep_set_state that can
    be called with disabled interrupts. However, this function is called with
    disabled interrupts only from speedstep_get_freqs, so it shouldn't cause
    any problem.

    Signed-off-by: Mikulas Patocka <mpatocka@redhat.com
    Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
    Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
    Signed-off-by: Kamal Mostafa <kamal@canonical.com>
    ---
    drivers/cpufreq/speedstep-lib.c | 3 +++
    drivers/cpufreq/speedstep-smi.c | 12 ++++++++++++
    2 files changed, 15 insertions(+)

    diff --git a/drivers/cpufreq/speedstep-lib.c b/drivers/cpufreq/speedstep-lib.c
    index 7047821..4ab7a21 100644
    --- a/drivers/cpufreq/speedstep-lib.c
    +++ b/drivers/cpufreq/speedstep-lib.c
    @@ -400,6 +400,7 @@ unsigned int speedstep_get_freqs(enum speedstep_processor processor,

    pr_debug("previous speed is %u\n", prev_speed);

    + preempt_disable();
    local_irq_save(flags);

    /* switch to low state */
    @@ -464,6 +465,8 @@ unsigned int speedstep_get_freqs(enum speedstep_processor processor,

    out:
    local_irq_restore(flags);
    + preempt_enable();
    +
    return ret;
    }
    EXPORT_SYMBOL_GPL(speedstep_get_freqs);
    diff --git a/drivers/cpufreq/speedstep-smi.c b/drivers/cpufreq/speedstep-smi.c
    index 0f5326d..34bd13c 100644
    --- a/drivers/cpufreq/speedstep-smi.c
    +++ b/drivers/cpufreq/speedstep-smi.c
    @@ -188,6 +188,7 @@ static void speedstep_set_state(unsigned int state)
    return;

    /* Disable IRQs */
    + preempt_disable();
    local_irq_save(flags);

    command = (smi_sig & 0xffffff00) | (smi_cmd & 0xff);
    @@ -198,9 +199,19 @@ static void speedstep_set_state(unsigned int state)

    do {
    if (retry) {
    + /*
    + * We need to enable interrupts, otherwise the blockage
    + * won't resolve.
    + *
    + * We disable preemption so that other processes don't
    + * run. If other processes were running, they could
    + * submit more DMA requests, making the blockage worse.
    + */
    pr_debug("retry %u, previous result %u, waiting...\n",
    retry, result);
    + local_irq_enable();
    mdelay(retry * 50);
    + local_irq_disable();
    }
    retry++;
    __asm__ __volatile__(
    @@ -217,6 +228,7 @@ static void speedstep_set_state(unsigned int state)

    /* enable IRQs */
    local_irq_restore(flags);
    + preempt_enable();

    if (new_state == state)
    pr_debug("change to %u MHz succeeded after %u tries "
    --
    1.9.1


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