dmaengine: ep93xx: Don't drain the transfers in terminate_all()

Draining the transfers in terminate_all callback happens with IRQs disabled,
therefore induces huge latency:

 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.
Move draining into device_synchronize callback.

Signed-off-by: Alexander Sverdlin <[email protected]>
Cc: [email protected]
Signed-off-by: Vinod Koul <[email protected]>

Author: sverdlin

drivers/dma/ep93xx_dma.c

@@ -201,6 +201,7 @@ struct ep93xx_dma_engine {
 	struct dma_device	dma_dev;
 	bool			m2m;
 	int			(*hw_setup)(struct ep93xx_dma_chan *);
+	void			(*hw_synchronize)(struct ep93xx_dma_chan *);
 	void			(*hw_shutdown)(struct ep93xx_dma_chan *);
 	void			(*hw_submit)(struct ep93xx_dma_chan *);
 	int			(*hw_interrupt)(struct ep93xx_dma_chan *);
@@ -333,21 +334,27 @@ static inline u32 m2p_channel_state(struct ep93xx_dma_chan *edmac)
 	return (readl(edmac->regs + M2P_STATUS) >> 4) & 0x3;
 }
 
-static void m2p_hw_shutdown(struct ep93xx_dma_chan *edmac)
+static void m2p_hw_synchronize(struct ep93xx_dma_chan *edmac)
 {
+	unsigned long flags;
 	u32 control;
 
+	spin_lock_irqsave(&edmac->lock, flags);
 	control = readl(edmac->regs + M2P_CONTROL);
 	control &= ~(M2P_CONTROL_STALLINT | M2P_CONTROL_NFBINT);
 	m2p_set_control(edmac, control);
+	spin_unlock_irqrestore(&edmac->lock, flags);
 
 	while (m2p_channel_state(edmac) >= M2P_STATE_ON)
-		cpu_relax();
+		schedule();
+}
 
+static void m2p_hw_shutdown(struct ep93xx_dma_chan *edmac)
+{
 	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)
@@ -1162,6 +1169,26 @@ ep93xx_dma_prep_dma_cyclic(struct dma_chan *chan, dma_addr_t dma_addr,
 	return NULL;
 }
 
+/**
+ * ep93xx_dma_synchronize - Synchronizes the termination of transfers to the
+ * current context.
+ * @chan: channel
+ *
+ * Synchronizes the DMA channel termination to the current context. When this
+ * function returns it is guaranteed that all transfers for previously issued
+ * descriptors have stopped and and it is safe to free the memory associated
+ * with them. Furthermore it is guaranteed that all complete callback functions
+ * for a previously submitted descriptor have finished running and it is safe to
+ * free resources accessed from within the complete callbacks.
+ */
+static void ep93xx_dma_synchronize(struct dma_chan *chan)
+{
+	struct ep93xx_dma_chan *edmac = to_ep93xx_dma_chan(chan);
+
+	if (edmac->edma->hw_synchronize)
+		edmac->edma->hw_synchronize(edmac);
+}
+
 /**
  * ep93xx_dma_terminate_all - terminate all transactions
  * @chan: channel
@@ -1325,6 +1352,7 @@ static int __init ep93xx_dma_probe(struct platform_device *pdev)
 	dma_dev->device_prep_slave_sg = ep93xx_dma_prep_slave_sg;
 	dma_dev->device_prep_dma_cyclic = ep93xx_dma_prep_dma_cyclic;
 	dma_dev->device_config = ep93xx_dma_slave_config;
+	dma_dev->device_synchronize = ep93xx_dma_synchronize;
 	dma_dev->device_terminate_all = ep93xx_dma_terminate_all;
 	dma_dev->device_issue_pending = ep93xx_dma_issue_pending;
 	dma_dev->device_tx_status = ep93xx_dma_tx_status;
@@ -1342,6 +1370,7 @@ static int __init ep93xx_dma_probe(struct platform_device *pdev)
 	} else {
 		dma_cap_set(DMA_PRIVATE, dma_dev->cap_mask);
 
+		edma->hw_synchronize = m2p_hw_synchronize;
 		edma->hw_setup = m2p_hw_setup;
 		edma->hw_shutdown = m2p_hw_shutdown;
 		edma->hw_submit = m2p_hw_submit;