Re: [PATCH] pwm: mxs: set pwm_chip can_sleep flag

[Alexandre Belloni <alexandre.belloni@free-electrons.com>]

On 08/04/2014 at 15:46:59 +0200, Stefan Wahren wrote :
> Hi Shawn,
> 
> Am 08.04.2014 13:29, schrieb Shawn Guo:
> > The .config() calls clk_get_rate() which might sleep, so we need to set
> > pwm_chip can_sleep flag.  Otherwise, we see the following warning when
> > using pwm driven heartbeat led.
> >
> > WARNING: CPU: 0 PID: 0 at kernel/locking/mutex.c:856 mutex_trylock+0x184/0x1a4()
> > DEBUG_LOCKS_WARN_ON(in_interrupt())
> > Modules linked in:
> > CPU: 0 PID: 0 Comm: swapper Not tainted 3.14.0-rc5 #18
> > [<c0015420>] (unwind_backtrace) from [<c0012cb0>] (show_stack+0x10/0x14)
> > [<c0012cb0>] (show_stack) from [<c001daf8>] (warn_slowpath_common+0x6c/0x8c)
> > [<c001daf8>] (warn_slowpath_common) from [<c001dbac>] (warn_slowpath_fmt+0x30/0x40)
> > [<c001dbac>] (warn_slowpath_fmt) from [<c045df74>] (mutex_trylock+0x184/0x1a4)
> > [<c045df74>] (mutex_trylock) from [<c0360950>] (clk_prepare_lock+0xc/0xec)
> > [<c0360950>] (clk_prepare_lock) from [<c0362020>] (clk_get_rate+0xc/0x68)
> > [<c0362020>] (clk_get_rate) from [<c028d07c>] (mxs_pwm_config+0x20/0x198)
> > [<c028d07c>] (mxs_pwm_config) from [<c028bde8>] (pwm_config+0x60/0x70)
> > [<c028bde8>] (pwm_config) from [<c034b61c>] (__led_pwm_set+0x1c/0x3c)
> > [<c034b61c>] (__led_pwm_set) from [<c034bc3c>] (led_heartbeat_function+0x70/0x110)
> > [<c034bc3c>] (led_heartbeat_function) from [<c00292f0>] (call_timer_fn+0x7c/0x164)
> > [<c00292f0>] (call_timer_fn) from [<c00295c8>] (run_timer_softirq+0x1f0/0x260)
> > [<c00295c8>] (run_timer_softirq) from [<c002255c>] (__do_softirq+0xc4/0x2f0)
> > [<c002255c>] (__do_softirq) from [<c0022890>] (irq_exit+0xa4/0x10c)
> > [<c0022890>] (irq_exit) from [<c0010240>] (handle_IRQ+0x34/0x84)
> > [<c0010240>] (handle_IRQ) from [<c0013524>] (__irq_svc+0x44/0x54)
> > [<c0013524>] (__irq_svc) from [<c00107f8>] (arch_cpu_idle+0x40/0x48)
> > [<c00107f8>] (arch_cpu_idle) from [<c005deb8>] (cpu_startup_entry+0x70/0x198)
> > [<c005deb8>] (cpu_startup_entry) from [<c060aac8>] (start_kernel+0x2a8/0x2f8)
> >
> > Reported-by: Stefan Wahren <stefan.wahren@i2se.com>
> > Signed-off-by: Shawn Guo <shawn.guo@freescale.com>
> > ---
> >  drivers/pwm/pwm-mxs.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/pwm/pwm-mxs.c b/drivers/pwm/pwm-mxs.c
> > index 9475bc7..4f1bb4e 100644
> > --- a/drivers/pwm/pwm-mxs.c
> > +++ b/drivers/pwm/pwm-mxs.c
> > @@ -147,6 +147,7 @@ static int mxs_pwm_probe(struct platform_device *pdev)
> >  	mxs->chip.dev = &pdev->dev;
> >  	mxs->chip.ops = &mxs_pwm_ops;
> >  	mxs->chip.base = -1;
> > +	mxs->chip.can_sleep = true;
> >  	ret = of_property_read_u32(np, "fsl,pwm-number", &mxs->chip.npwm);
> >  	if (ret < 0) {
> >  		dev_err(&pdev->dev, "failed to get pwm number: %d\n", ret);
> 
> thanks for the patch. I've tested it with our i.MX28 board and the
> warning above never came. So it works.
> Unfortunately the led still don't behave as expected. If i set the led
> trigger to heartbeat the led goes on and stays in this state.
> 
> May be this has something to do with the following discussion
> 
> http://comments.gmane.org/gmane.linux.leds/208
> 

This may be but the solution is not correct we want to keep disabling
the pwm when brightness is 0. Can you try the latest series from
Russell:

http://thread.gmane.org/gmane.linux.leds/579 and set active_low but keep
the pwm polarity normal.

Regards,

-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com