[PATCH v2 1/2] dmaengine: ep93xx: Always start from BASE0

[PATCH v2 1/2] dmaengine: ep93xx: Always start from BASE0

[Alexander Sverdlin]

The current buffer is being reset to zero on device_free_chan_resources()
but not on device_terminate_all(). It could happen that HW is restarted and
expects BASE0 to be used, but the driver is not synchronized and will start
from BASE1. One solution is to reset the buffer explicitly in
m2p_hw_setup().

Signed-off-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Cc: stable@vger.kernel.org
---
 drivers/dma/ep93xx_dma.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/dma/ep93xx_dma.c b/drivers/dma/ep93xx_dma.c
index d37e8dda8079..deb009c3121f 100644
--- a/drivers/dma/ep93xx_dma.c
+++ b/drivers/dma/ep93xx_dma.c
@@ -323,6 +323,8 @@ static int m2p_hw_setup(struct ep93xx_dma_chan *edmac)
 		| M2P_CONTROL_ENABLE;
 	m2p_set_control(edmac, control);
 
+	edmac->buffer = 0;
+
 	return 0;
 }
 
-- 
2.12.2

[PATCH v2 2/2] dmaengine: ep93xx: Don't drain the transfers in terminate_all()

[Alexander Sverdlin]

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 <alexander.sverdlin@gmail.com>
Cc: stable@vger.kernel.org
---
 drivers/dma/ep93xx_dma.c | 37 +++++++++++++++++++++++++++++++++----
 1 file changed, 33 insertions(+), 4 deletions(-)

diff --git a/drivers/dma/ep93xx_dma.c b/drivers/dma/ep93xx_dma.c
index deb009c3121f..e5289d117960 100644
--- a/drivers/dma/ep93xx_dma.c
+++ b/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)
@@ -1163,6 +1170,26 @@ ep93xx_dma_prep_dma_cyclic(struct dma_chan *chan, dma_addr_t dma_addr,
 }
 
 /**
+ * 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 assoicated
+ * 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;
-- 
2.12.2

Re: [PATCH v2 2/2] dmaengine: ep93xx: Don't drain the transfers in terminate_all()

[Vinod Koul]

On Wed, May 17, 2017 at 07:33:54PM +0200, Alexander Sverdlin wrote:

>  /**
> + * 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 assoicated

s/assoicated/associated

-- 
~Vinod