DMA: PL08x: fix infinite wait when terminating transfers

If we try to pause a channel when terminating a transfer, we could end
up spinning for it to become inactive indefinitely, and can result in
an uninterruptible wait requiring a reset to recover from.

Terminating a transfer is supposed to take effect immediately, but may
result in data loss.

To make this clear, rename the function to pl08x_terminate_phy_chan().
Also, make sure it is always consistently called - with the spinlock
held and IRQs disabled, and ensure that the TC and ERR interrupt status
is always cleared.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Acked-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 18 insertions, 14 deletions

diff --git a/drivers/dma/amba-pl08x.c b/drivers/dma/amba-pl08x.c
index 297f48b0cba9..8321a3997c95 100644
--- a/drivers/dma/amba-pl08x.c
+++ b/drivers/dma/amba-pl08x.c
@@ -267,19 +267,24 @@ static void pl08x_resume_phy_chan(struct pl08x_phy_chan *ch)
 }
 
 
-/* Stops the channel */
-static void pl08x_stop_phy_chan(struct pl08x_phy_chan *ch)
+/*
+ * pl08x_terminate_phy_chan() stops the channel, clears the FIFO and
+ * clears any pending interrupt status.  This should not be used for
+ * an on-going transfer, but as a method of shutting down a channel
+ * (eg, when it's no longer used) or terminating a transfer.
+ */
+static void pl08x_terminate_phy_chan(struct pl08x_driver_data *pl08x,
+        struct pl08x_phy_chan *ch)
 {
-        u32 val;
+        u32 val = readl(ch->base + PL080_CH_CONFIG);
 
-        pl08x_pause_phy_chan(ch);
+        val &= ~(PL080_CONFIG_ENABLE | PL080_CONFIG_ERR_IRQ_MASK |
+                 PL080_CONFIG_TC_IRQ_MASK);
 
-        /* Disable channel */
-        val = readl(ch->base + PL080_CH_CONFIG);
-        val &= ~PL080_CONFIG_ENABLE;
-        val &= ~PL080_CONFIG_ERR_IRQ_MASK;
-        val &= ~PL080_CONFIG_TC_IRQ_MASK;
         writel(val, ch->base + PL080_CH_CONFIG);
+
+        writel(1 << ch->id, pl08x->base + PL080_ERR_CLEAR);
+        writel(1 << ch->id, pl08x->base + PL080_TC_CLEAR);
 }
 
 static inline u32 get_bytes_in_cctl(u32 cctl)
@@ -404,13 +409,12 @@ static inline void pl08x_put_phy_channel(struct pl08x_driver_data *pl08x,
 {
         unsigned long flags;
 
+        spin_lock_irqsave(&ch->lock, flags);
+
         /* Stop the channel and clear its interrupts */
-        pl08x_stop_phy_chan(ch);
-        writel((1 << ch->id), pl08x->base + PL080_ERR_CLEAR);
-        writel((1 << ch->id), pl08x->base + PL080_TC_CLEAR);
+        pl08x_terminate_phy_chan(pl08x, ch);
 
         /* Mark it as free */
-        spin_lock_irqsave(&ch->lock, flags);
         ch->serving = NULL;
         spin_unlock_irqrestore(&ch->lock, flags);
 }
@@ -1449,7 +1453,7 @@ static int pl08x_control(struct dma_chan *chan, enum dma_ctrl_cmd cmd,
                 plchan->state = PL08X_CHAN_IDLE;
 
                 if (plchan->phychan) {
-                        pl08x_stop_phy_chan(plchan->phychan);
+                        pl08x_terminate_phy_chan(pl08x, plchan->phychan);
 
                         /*
                          * Mark physical channel as free and free any slave