Re: imx sgtl5000:BUG: scheduling while atomic: speaker-test/1225/0x00000003

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Hi,

Richard Zhao writes:
> On Thu, Apr 26, 2012 at 08:10:35AM +0200, Lothar Waßmann wrote:
> > Hi,
> > 
> > [added CC: Sascha Hauer as the SDMA driver author]
> > 
> > Richard Zhao writes:
> > > On Thu, Apr 26, 2012 at 10:33:21AM +0800, Richard Zhao wrote:
> > > > [   13.901890] eth0: no IPv6 routers present
> > > > [   70.295079] BUG: scheduling while atomic: speaker-test/1225/0x00000003
> > > > [   70.304293] Modules linked in:
> > > > [   70.310389] [<c0015a68>] (unwind_backtrace+0x0/0xec) from [<c0585810>] (dump_stack+0x20/0x24)
> > > > [   70.310421] [<c0585810>] (dump_stack+0x20/0x24) from [<c0585f6c>] (__schedule_bug+0x54/0x60)
> > > > [   70.310452] [<c0585f6c>] (__schedule_bug+0x54/0x60) from [<c058db64>] (__schedule+0x84/0x748)
> > > > [   70.310476] [<c058db64>] (__schedule+0x84/0x748) from [<c058e310>] (schedule+0x8c/0x90)
> > > > [   70.310500] [<c058e310>] (schedule+0x8c/0x90) from [<c058c504>] (schedule_timeout+0x2fc/0x35c)
> > > > [   70.310541] [<c058c504>] (schedule_timeout+0x2fc/0x35c) from [<c058d970>] (wait_for_common+0xd8/0x16c)
> > > > [   70.310567] [<c058d970>] (wait_for_common+0xd8/0x16c) from [<c058da44>] (wait_for_completion_timeout+0x1c/0x20)
> > > > [   70.310604] [<c058da44>] (wait_for_completion_timeout+0x1c/0x20) from [<c03352bc>] (sdma_run_channel+0x70/0x8c)
> > > > [   70.310634] [<c03352bc>] (sdma_run_channel+0x70/0x8c) from [<c0335614>] (sdma_load_context+0x188/0x19c)
> > > > [   70.310661] [<c0335614>] (sdma_load_context+0x188/0x19c) from [<c0335688>] (sdma_prep_dma_cyclic+0x60/0x1a8)
> > > > [   70.310694] [<c0335688>] (sdma_prep_dma_cyclic+0x60/0x1a8) from [<c04760f4>] (snd_dmaengine_pcm_trigger+0xa0/0x134)
> > > > [   70.310729] [<c04760f4>] (snd_dmaengine_pcm_trigger+0xa0/0x134) from [<c0483e68>] (soc_pcm_trigger+0x74/0xb0)
> > > > [   70.310770] [<c0483e68>] (soc_pcm_trigger+0x74/0xb0) from [<c046e670>] (snd_pcm_do_start+0x34/0x40)
> > > > [   70.310797] [<c046e670>] (snd_pcm_do_start+0x34/0x40) from [<c046e288>] (snd_pcm_action_single+0x48/0x74)
> > > > [   70.310823] [<c046e288>] (snd_pcm_action_single+0x48/0x74) from [<c046e334>] (snd_pcm_action+0x80/0x8c)
> > > > [   70.310850] [<c046e334>] (snd_pcm_action+0x80/0x8c) from [<c04707f0>] (snd_pcm_start+0x24/0x2c)
> > > > [   70.310877] [<c04707f0>] (snd_pcm_start+0x24/0x2c) from [<c0474058>] (snd_pcm_lib_write1+0x2a8/0x340)
> > > > [   70.310900] [<c0474058>] (snd_pcm_lib_write1+0x2a8/0x340) from [<c04741d0>] (snd_pcm_lib_write+0x70/0x7c)
> > > > [   70.311007] [<c04741d0>] (snd_pcm_lib_write+0x70/0x7c) from [<c04703f8>] (snd_pcm_playback_ioctl1+0x114/0x428)
> > > > [   70.311038] [<c04703f8>] (snd_pcm_playback_ioctl1+0x114/0x428) from [<c0470744>] (snd_pcm_playback_ioctl+0x38/0x44)
> > > > [   70.311077] [<c0470744>] (snd_pcm_playback_ioctl+0x38/0x44) from [<c0107234>] (do_vfs_ioctl+0x4f4/0x568)
> > > > [   70.311105] [<c0107234>] (do_vfs_ioctl+0x4f4/0x568) from [<c0107308>] (sys_ioctl+0x60/0x84)
> > > > [   70.311138] [<c0107308>] (sys_ioctl+0x60/0x84) from [<c000df40>] (ret_fast_syscall+0x0/0x30)
> > > > [   80.301928] ALSA sound/core/pcm_lib.c:1853 playback write error (DMA or IRQ trouble?)
> > > > 
> > > > 
> > > > kernel: 3.4rc3 with ASoC/for-next and some my patches.
> > > 
> > > I found the cause.
> > > snd_dmaengine_pcm_trigger --> dmaengine_pcm_prepare_and_submit
> > > --> dmaengine_prep_dma_cyclic
> > > 
> > > The trigger function is in atomic context, but dmaengine_prep_dma_cyclic
> > > tried to sleep.
> > > 
> > > From dma engine design, can device_prep_dma_cyclic sleep?
> > > If yes, we may need to move it out of trigger functions.
> > > 
> > The root cause is that sdma_run_channel does a
> > wait_for_completion_timeout() to wait for the special channel 0 to
> > complete which is complete overkill from my point of view.
> > channel 0 is used internally in the DMA engine and should always
> > complete within a few microseconds. Thus a busy loop with a timeout
> > would be fine here.
> > 
> > Furthermore a mutex is used to serialize access to channel data
> > structures which also forbids the affected function to be used in
> > interrupt context.
> Only when dma engine declare dev_prep_xxx can not sleep, we need your patch.
> > 
> > The following patch would fix that:
> > diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c
> > index d3e38e2..fcab768 100644
> > --- a/drivers/dma/imx-sdma.c
> > +++ b/drivers/dma/imx-sdma.c
> > @@ -24,7 +24,7 @@
> >  #include <linux/mm.h>
> >  #include <linux/interrupt.h>
> >  #include <linux/clk.h>
> > -#include <linux/wait.h>
> > +#include <linux/delay.h>
> >  #include <linux/sched.h>
> >  #include <linux/semaphore.h>
> >  #include <linux/spinlock.h>
> > @@ -323,7 +323,7 @@ struct sdma_engine {
> >  	dma_addr_t			context_phys;
> >  	struct dma_device		dma_device;
> >  	struct clk			*clk;
> > -	struct mutex			channel_0_lock;
> > +	spinlock_t			channel_0_lock;
> >  	struct sdma_script_start_addrs	*script_addrs;
> >  };
> >  
> > @@ -408,12 +408,21 @@ static int sdma_run_channel(struct sdma_channel *sdmac)
> Since you're polling, change function name specific to channel 0?
> >  	struct sdma_engine *sdma = sdmac->sdma;
> >  	int channel = sdmac->channel;
> >  	int ret;
> > -
> > -	init_completion(&sdmac->done);
> > +	unsigned long timeout = 500;
> I'm not sure. Did you test 500us is enough for loading firmware?
>
Channel 0 is not used for actual data transfer but for some internal
housekeeping. Thus the timeout is independent from the time required
for the actual data transfer.
I haven't seen any timeout even with the timeout set to 100us.
Usually it takes 3 to 4 us to complete.

> >  	sdma_enable_channel(sdma, channel);
> >  
> You didn't disable the irq. mxc_sdma_handle_channel may be called.
>
The calls to sdma_run_channel() are framed with
spinlock_irq_save()/spin_unlock_irqrestore().

> > -	ret = wait_for_completion_timeout(&sdmac->done, HZ);
> > +	while (!(ret = readl_relaxed(sdma->regs + SDMA_H_INTR) & 1)) {
> > +		if (timeout-- <= 0)
> > +			break;
> > +		udelay(1);
> > +	}
> > +	if (ret) {
> > +		/* Clear the interrupt status */
> > +		writel_relaxed(ret, sdma->regs + SDMA_H_INTR);
> > +	} else {
> > +		dev_err(sdma->dev, "Timeout waiting for CH0 ready\n");
> > +	}
> >  
> >  	return ret ? 0 : -ETIMEDOUT;
> >  }
> > @@ -425,17 +434,17 @@ static int sdma_load_script(struct sdma_engine *sdma, void *buf, int size,
> >  	void *buf_virt;
> >  	dma_addr_t buf_phys;
> >  	int ret;
> > -
> > -	mutex_lock(&sdma->channel_0_lock);
> > +	unsigned long flags;
> >  
> >  	buf_virt = dma_alloc_coherent(NULL,
> >  			size,
> >  			&buf_phys, GFP_KERNEL);
> >  	if (!buf_virt) {
> > -		ret = -ENOMEM;
> > -		goto err_out;
> > +		return -ENOMEM;
> >  	}
> >  
> > +	spin_lock_irqsave(&sdma->channel_0_lock, flags);
> > +
> >  	bd0->mode.command = C0_SETPM;
> >  	bd0->mode.status = BD_DONE | BD_INTR | BD_WRAP | BD_EXTD;
> >  	bd0->mode.count = size / 2;
> > @@ -446,10 +455,9 @@ static int sdma_load_script(struct sdma_engine *sdma, void *buf, int size,
> >  
> >  	ret = sdma_run_channel(&sdma->channel[0]);
> >  
> > -	dma_free_coherent(NULL, size, buf_virt, buf_phys);
> > +	spin_unlock_irqrestore(&sdma->channel_0_lock, flags);
> >  
> > -err_out:
> > -	mutex_unlock(&sdma->channel_0_lock);
> > +	dma_free_coherent(NULL, size, buf_virt, buf_phys);
> >  
> >  	return ret;
> >  }
> > @@ -539,7 +547,7 @@ static void mxc_sdma_handle_channel(struct sdma_channel *sdmac)
> >  	complete(&sdmac->done);
> >  
> >  	/* not interested in channel 0 interrupts */
> > -	if (sdmac->channel == 0)
> > +	if (WARN_ON(sdmac->channel == 0))
> >  		return;
> Move it before complete?
> 
Shouldn't matter since it should never be reached anyway.


Lothar Waßmann
-- 
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