linux-kernel - Re: [PATCH v4 2/4] drm/rockchip: add an common abstracted PSR driver

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Date:	Fri, 22 Jul 2016 21:04:41 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	Yakir Yang <ykk@...k-chips.com>
Cc:	Mark Yao <yzq@...k-chips.com>, Inki Dae <inki.dae@...sung.com>,
	Jingoo Han <jingoohan1@...il.com>,
	Heiko Stuebner <heiko@...ech.de>,
	Javier Martinez Canillas <javier@....samsung.com>,
	Stéphane Marchesin <marcheu@...omium.org>,
	Sean Paul <seanpaul@...omium.org>,
	Tomasz Figa <tfiga@...omium.org>,
	David Airlie <airlied@...ux.ie>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Thierry Reding <treding@...dia.com>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Emil Velikov <emil.l.velikov@...il.com>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	"open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>
Subject: Re: [PATCH v4 2/4] drm/rockchip: add an common abstracted PSR driver

Yakir,

On Wed, Jul 13, 2016 at 9:15 PM, Yakir Yang <ykk@...k-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