MX28: leds/pwm: Using pwm driven led as heartbeat leads to kernel warning
alexandre.belloni at free-electrons.com
Tue Apr 8 00:59:16 PDT 2014
On 08/04/2014 at 15:34:04 +0800, Shawn Guo wrote :
> On Fri, Apr 04, 2014 at 06:44:47PM +0200, Alexandre Belloni wrote:
> > On 04/04/2014 at 22:26:58 +0800, Shawn Guo wrote :
> > > On Fri, Apr 04, 2014 at 03:54:52PM +0200, Stefan Wahren wrote:
> > > > the problem is still reproducable in Mainline 3.14.0 and gives the same
> > > > warning message.
> > > > Also i add linux-leds in CC.
> > > >
> > > > Are there any advices to narrow down the problem?
> > > >
> > > > Is this problem specific to i.MX28 PWM (i don't have other kind of
> > > > hardware)?
> > >
> > > I don't think it's specific to i.MX28 PWM. Since the .config hook of
> > > pwm_ops will be called from interrupt context in this case, any pwm
> > > drivers that do sleeping calls in the hook will have this problem, e.g.
> > > the clk APIs that hold mutex like clk_prepare() and clk_get_rate() etc.
> > >
> > Yeah, I'm wondering whether we should set pwm->chip->can_sleep then.
> Right, per kerneldoc of struct pwm_chip, we should set can_sleep.
> * struct pwm_chip - abstract a PWM controller
> * ...
> * @can_sleep: must be true if the .config(), .enable() or .disable()
> * operations may sleep
> But how does setting the flag make a difference there? I see pwm core
> does nothing about the flag, or am I missing something?
The driver using the PWM should test the flag, have a look at:
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
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