Re: [PATCH 2/2] dmaengine: ep93xx: Don't drain the transfers in terminate_all()

[Vinod Koul <vinod.koul@intel.com>]

On Sun, May 14, 2017 at 12:13:27AM +0200, Alexander Sverdlin wrote:
> As dmaengine.h suggests, device_terminate_all() "Aborts all transfers on a
> channel". Seems that no other driver tried to busy-wait and actually drain
> the data. Moreover, this happens with IRQs disabled, therefore induces huge
> latency:

Perhaps you should move current code to device_synchronize callback to allow
people to do so, if desired.

> 
>  irqsoff latency trace v1.1.5 on 4.11.0
>  --------------------------------------------------------------------
>  latency: 39770 us, #57/57, CPU#0 | (M:preempt VP:0, KP:0, SP:0 HP:0)
>     -----------------
>     | task: process-129 (uid:0 nice:0 policy:2 rt_prio:50)
>     -----------------
>   => started at: _snd_pcm_stream_lock_irqsave
>   => ended at:   snd_pcm_stream_unlock_irqrestore
> 
>                   _------=> CPU#
>                  / _-----=> irqs-off
>                 | / _----=> need-resched
>                 || / _---=> hardirq/softirq
>                 ||| / _--=> preempt-depth
>                 |||| /     delay
>   cmd     pid   ||||| time  |   caller
>      \   /      |||||  \    |   /
> process-129     0d.s.    3us : _snd_pcm_stream_lock_irqsave
> process-129     0d.s1    9us : snd_pcm_stream_lock <-_snd_pcm_stream_lock_irqsave
> process-129     0d.s1   15us : preempt_count_add <-snd_pcm_stream_lock
> process-129     0d.s2   22us : preempt_count_add <-snd_pcm_stream_lock
> process-129     0d.s3   32us : snd_pcm_update_hw_ptr0 <-snd_pcm_period_elapsed
> process-129     0d.s3   41us : soc_pcm_pointer <-snd_pcm_update_hw_ptr0
> process-129     0d.s3   50us : dmaengine_pcm_pointer <-soc_pcm_pointer
> process-129     0d.s3   58us+: snd_dmaengine_pcm_pointer_no_residue <-dmaengine_pcm_pointer
> process-129     0d.s3   96us : update_audio_tstamp <-snd_pcm_update_hw_ptr0
> process-129     0d.s3  103us : snd_pcm_update_state <-snd_pcm_update_hw_ptr0
> process-129     0d.s3  112us : xrun <-snd_pcm_update_state
> process-129     0d.s3  119us : snd_pcm_stop <-xrun
> process-129     0d.s3  126us : snd_pcm_action <-snd_pcm_stop
> process-129     0d.s3  134us : snd_pcm_action_single <-snd_pcm_action
> process-129     0d.s3  141us : snd_pcm_pre_stop <-snd_pcm_action_single
> process-129     0d.s3  150us : snd_pcm_do_stop <-snd_pcm_action_single
> process-129     0d.s3  157us : soc_pcm_trigger <-snd_pcm_do_stop
> process-129     0d.s3  166us : snd_dmaengine_pcm_trigger <-soc_pcm_trigger
> process-129     0d.s3  175us : ep93xx_dma_terminate_all <-snd_dmaengine_pcm_trigger
> process-129     0d.s3  182us : preempt_count_add <-ep93xx_dma_terminate_all
> process-129     0d.s4  189us*: m2p_hw_shutdown <-ep93xx_dma_terminate_all
> process-129     0d.s4 39472us : m2p_hw_setup <-ep93xx_dma_terminate_all
> 
>  ... rest skipped...
> 
> process-129     0d.s. 40080us : <stack trace>
>  => ep93xx_dma_tasklet
>  => tasklet_action
>  => __do_softirq
>  => irq_exit
>  => __handle_domain_irq
>  => vic_handle_irq
>  => __irq_usr
>  => 0xb66c6668
> 
> Just abort the transfers and warn if the HW state is not what we expect.
> 
> Signed-off-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
> Cc: stable@vger.kernel.org
> ---
>  drivers/dma/ep93xx_dma.c | 13 ++-----------
>  1 file changed, 2 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/dma/ep93xx_dma.c b/drivers/dma/ep93xx_dma.c
> index a3d946d2a8e1..e78d1fbf2179 100644
> --- a/drivers/dma/ep93xx_dma.c
> +++ b/drivers/dma/ep93xx_dma.c
> @@ -345,19 +345,10 @@ static inline u32 m2p_channel_state(struct ep93xx_dma_chan *edmac)
>  
>  static void m2p_hw_shutdown(struct ep93xx_dma_chan *edmac)
>  {
> -	u32 control;
> -
> -	control = readl(edmac->regs + M2P_CONTROL);
> -	control &= ~(M2P_CONTROL_STALLINT | M2P_CONTROL_NFBINT);
> -	m2p_set_control(edmac, control);
> -
> -	while (m2p_channel_state(edmac) >= M2P_STATE_ON)
> -		cpu_relax();
> -
>  	m2p_set_control(edmac, 0);
>  
> -	while (m2p_channel_state(edmac) == M2P_STATE_STALL)
> -		cpu_relax();
> +	while (m2p_channel_state(edmac) != M2P_STATE_IDLE)
> +		dev_warn(chan2dev(edmac), "M2P: Not yet IDLE\n");
>  }
>  
>  static void m2p_fill_desc(struct ep93xx_dma_chan *edmac)
> -- 
> 2.12.2
> 

-- 
~Vinod