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From: Doug Anderson <dianders@chromium.org>
Date: Fri, 22 Jul 2016 21:04:41 -0700
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Subject: Re: [PATCH v4 2/4] drm/rockchip: add an common abstracted PSR driver
To: Yakir Yang <ykk@rock-chips.com>
Cc: Mark Yao <yzq@rock-chips.com>, Inki Dae <inki.dae@samsung.com>,
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Yakir,

On Wed, Jul 13, 2016 at 9:15 PM, Yakir Yang <ykk@rock-chips.com> wrote:
> +static void psr_set_state(struct psr_drv *psr, enum psr_state state)
> +{
> +       mutex_lock(&psr->state_mutex);
> +
> +       if (psr->state == state) {
> +               mutex_unlock(&psr->state_mutex);
> +               return;
> +       }
> +
> +       psr->state = state;
> +       switch (state) {
> +       case PSR_ENABLE:
> +               psr->set(psr->encoder, true);
> +               break;
> +
> +       case PSR_DISABLE:
> +       case PSR_FLUSH:
> +               psr->set(psr->encoder, false);
> +               break;
> +       };
> +
> +       mutex_unlock(&psr->state_mutex);
> +}
> +
> +static void psr_flush_handler(unsigned long data)
> +{
> +       struct psr_drv *psr = (struct psr_drv *)data;
> +
> +       if (!psr || psr->state != PSR_FLUSH)
> +               return;
> +
> +       psr_set_state(psr, PSR_ENABLE);

As mentioned in a separate thread, this is probably not OK.
psr_set_state() grabs a mutex and that might sleep.  ...but
psr_flush_handler() is a timer.  I'm nearly certain that timers can't
sleep.

I believe this is the source of "sleeping function called from invalid
context" that I've seen at times.

-Doug