dma40: ensure event lines get enabled

The controller sometimes fails to register the enable of the event line when
both src and dst event lines are used on the same logical channel.  Implement
the recommended software workaround, which is to retry the write until it
works.
Acked-by: NPer Forlin <per.forlin@stericsson.com>
Acked-by: NJonas Aaberg <jonas.aberg@stericsson.com>
Signed-off-by: NRabin Vincent <rabin.vincent@stericsson.com>
Signed-off-by: NLinus Walleij <linus.walleij@stericsson.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

drivers/dma/ste_dma40.c

@@ -303,6 +303,11 @@ struct d40_reg_val {
 	unsigned int val;
 };
 
+static struct device *chan2dev(struct d40_chan *d40c)
+{
+	return &d40c->chan.dev->device;
+}
+
 static int d40_pool_lli_alloc(struct d40_desc *d40d,
 			      int lli_len, bool is_log)
 {
@@ -701,17 +706,46 @@ static void d40_term_all(struct d40_chan *d40c)
 	d40c->busy = false;
 }
 
+static void __d40_config_set_event(struct d40_chan *d40c, bool enable,
+				   u32 event, int reg)
+{
+	void __iomem *addr = d40c->base->virtbase + D40_DREG_PCBASE
+			     + d40c->phy_chan->num * D40_DREG_PCDELTA + reg;
+	int tries;
+
+	if (!enable) {
+		writel((D40_DEACTIVATE_EVENTLINE << D40_EVENTLINE_POS(event))
+		       | ~D40_EVENTLINE_MASK(event), addr);
+		return;
+	}
+
+	/*
+	 * The hardware sometimes doesn't register the enable when src and dst
+	 * event lines are active on the same logical channel.  Retry to ensure
+	 * it does.  Usually only one retry is sufficient.
+	 */
+	tries = 100;
+	while (--tries) {
+		writel((D40_ACTIVATE_EVENTLINE << D40_EVENTLINE_POS(event))
+		       | ~D40_EVENTLINE_MASK(event), addr);
+
+		if (readl(addr) & D40_EVENTLINE_MASK(event))
+			break;
+	}
+
+	if (tries != 99)
+		dev_dbg(chan2dev(d40c),
+			"[%s] workaround enable S%cLNK (%d tries)\n",
+			__func__, reg == D40_CHAN_REG_SSLNK ? 'S' : 'D',
+			100 - tries);
+
+	WARN_ON(!tries);
+}
+
 static void d40_config_set_event(struct d40_chan *d40c, bool do_enable)
 {
-	u32 val;
 	unsigned long flags;
 
-	/* Notice, that disable requires the physical channel to be stopped */
-	if (do_enable)
-		val = D40_ACTIVATE_EVENTLINE;
-	else
-		val = D40_DEACTIVATE_EVENTLINE;
-
 	spin_lock_irqsave(&d40c->phy_chan->lock, flags);
 
 	/* Enable event line connected to device (or memcpy) */
@@ -719,20 +753,15 @@ static void d40_config_set_event(struct d40_chan *d40c, bool do_enable)
 	    (d40c->dma_cfg.dir == STEDMA40_PERIPH_TO_PERIPH)) {
 		u32 event = D40_TYPE_TO_EVENT(d40c->dma_cfg.src_dev_type);
 
-		writel((val << D40_EVENTLINE_POS(event)) |
-		       ~D40_EVENTLINE_MASK(event),
-		       d40c->base->virtbase + D40_DREG_PCBASE +
-		       d40c->phy_chan->num * D40_DREG_PCDELTA +
-		       D40_CHAN_REG_SSLNK);
+		__d40_config_set_event(d40c, do_enable, event,
+				       D40_CHAN_REG_SSLNK);
 	}
+
 	if (d40c->dma_cfg.dir !=  STEDMA40_PERIPH_TO_MEM) {
 		u32 event = D40_TYPE_TO_EVENT(d40c->dma_cfg.dst_dev_type);
 
-		writel((val << D40_EVENTLINE_POS(event)) |
-		       ~D40_EVENTLINE_MASK(event),
-		       d40c->base->virtbase + D40_DREG_PCBASE +
-		       d40c->phy_chan->num * D40_DREG_PCDELTA +
-		       D40_CHAN_REG_SDLNK);
+		__d40_config_set_event(d40c, do_enable, event,
+				       D40_CHAN_REG_SDLNK);
 	}
 
 	spin_unlock_irqrestore(&d40c->phy_chan->lock, flags);