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    Subject[PATCH 5.7 350/376] pwm: lpss: Fix get_state runtime-pm reference handling
    Date
    From: Hans de Goede <hdegoede@redhat.com>

    commit 01aa905d4791da7d3630f6030ff99d58105cca00 upstream.

    Before commit cfc4c189bc70 ("pwm: Read initial hardware state at request
    time"), a driver's get_state callback would get called once per PWM from
    pwmchip_add().

    pwm-lpss' runtime-pm code was relying on this, getting a runtime-pm ref for
    PWMs which are enabled at probe time from within its get_state callback,
    before enabling runtime-pm.

    The change to calling get_state at request time causes a number of
    problems:

    1. PWMs enabled at probe time may get runtime suspended before they are
    requested, causing e.g. a LCD backlight controlled by the PWM to turn off.

    2. When the request happens when the PWM has been runtime suspended, the
    ctrl register will read all 1 / 0xffffffff, causing get_state to store
    bogus values in the pwm_state.

    3. get_state was using an async pm_runtime_get() call, because it assumed
    that runtime-pm has not been enabled yet. If shortly after the request an
    apply call is made, then the pwm_lpss_is_updating() check may trigger
    because the resume triggered by the pm_runtime_get() call is not complete
    yet, so the ctrl register still reads all 1 / 0xffffffff.

    This commit fixes these issues by moving the initial pm_runtime_get() call
    for PWMs which are enabled at probe time to the pwm_lpss_probe() function;
    and by making get_state take a runtime-pm ref before reading the ctrl reg.

    BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=1828927
    Fixes: cfc4c189bc70 ("pwm: Read initial hardware state at request time")
    Cc: stable@vger.kernel.org
    Signed-off-by: Hans de Goede <hdegoede@redhat.com>
    Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
    Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/pwm/pwm-lpss.c | 15 +++++++++++----
    1 file changed, 11 insertions(+), 4 deletions(-)

    --- a/drivers/pwm/pwm-lpss.c
    +++ b/drivers/pwm/pwm-lpss.c
    @@ -158,7 +158,6 @@ static int pwm_lpss_apply(struct pwm_chi
    return 0;
    }

    -/* This function gets called once from pwmchip_add to get the initial state */
    static void pwm_lpss_get_state(struct pwm_chip *chip, struct pwm_device *pwm,
    struct pwm_state *state)
    {
    @@ -167,6 +166,8 @@ static void pwm_lpss_get_state(struct pw
    unsigned long long base_unit, freq, on_time_div;
    u32 ctrl;

    + pm_runtime_get_sync(chip->dev);
    +
    base_unit_range = BIT(lpwm->info->base_unit_bits);

    ctrl = pwm_lpss_read(pwm);
    @@ -187,8 +188,7 @@ static void pwm_lpss_get_state(struct pw
    state->polarity = PWM_POLARITY_NORMAL;
    state->enabled = !!(ctrl & PWM_ENABLE);

    - if (state->enabled)
    - pm_runtime_get(chip->dev);
    + pm_runtime_put(chip->dev);
    }

    static const struct pwm_ops pwm_lpss_ops = {
    @@ -202,7 +202,8 @@ struct pwm_lpss_chip *pwm_lpss_probe(str
    {
    struct pwm_lpss_chip *lpwm;
    unsigned long c;
    - int ret;
    + int i, ret;
    + u32 ctrl;

    if (WARN_ON(info->npwm > MAX_PWMS))
    return ERR_PTR(-ENODEV);
    @@ -232,6 +233,12 @@ struct pwm_lpss_chip *pwm_lpss_probe(str
    return ERR_PTR(ret);
    }

    + for (i = 0; i < lpwm->info->npwm; i++) {
    + ctrl = pwm_lpss_read(&lpwm->chip.pwms[i]);
    + if (ctrl & PWM_ENABLE)
    + pm_runtime_get(dev);
    + }
    +
    return lpwm;
    }
    EXPORT_SYMBOL_GPL(pwm_lpss_probe);

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