dmaengine: rcar-dmac: Fix release resources after interrupt process

This patch fixes the problem that occasionally released resources
before the end of interrupt processing.

[   58.156412] Unable to handle kernel NULL pointer dereference at virtual
 address 00000000
[   58.166155] pgd = ffff8006f78b0000
[   58.169822] [00000000] *pgd=000000073773b003 , *pud=0000000737c70003 ,
 *pmd=0000000000000000
[   58.179738]
[   58.181548] Internal error: Oops: 96000046 [#1] PREEMPT SMP
[   58.187484] Modules linked in:
[   58.190919] CPU: 0 PID: 2898 Comm: dma_ioctl Not tainted 4.9.0-00002-g501
07f2-dirty xen-troops#147
[   58.199438] Hardware name: Renesas Salvator-X board based on r8a7795 (DT)
[   58.206680] task: ffff8006f77b1900 task.stack: ffff8006f7bd4000
[   58.213090] PC is at rcar_dmac_chan_prep_sg+0xa4/0x3f0
[   58.218725] LR is at rcar_dmac_chan_prep_sg+0x6c/0x3f0

Signed-off-by: Hiroyuki Yokoyama <hiroyuki.yokoyama.vx@renesas.com>

drivers/dma/sh/rcar-dmac.c

@@ -1263,6 +1263,24 @@ static int rcar_dmac_chan_terminate_all(struct dma_chan *chan)
 	return 0;
 }
 
+static void rcar_dmac_synchronize(struct dma_chan *chan)
+{
+	struct rcar_dmac_chan *rchan = to_rcar_dmac_chan(chan);
+	struct rcar_dmac *dmac = to_rcar_dmac(chan->device);
+	struct platform_device *pdev = to_platform_device(dmac->dev);
+	int irq;
+	char pdev_irqname[5];
+
+	sprintf(pdev_irqname, "ch%u", rchan->index);
+	irq = platform_get_irq_byname(pdev, pdev_irqname);
+	if (irq < 0) {
+		dev_err(dmac->dev, "no IRQ specified for channel %u\n",
+			rchan->index);
+		return;
+	}
+	synchronize_irq(irq);
+}
+
 static unsigned int rcar_dmac_chan_get_residue(struct rcar_dmac_chan *chan,
 					       dma_cookie_t cookie)
 {
@@ -1901,6 +1919,7 @@ static int rcar_dmac_probe(struct platform_device *pdev)
 	engine->device_config = rcar_dmac_device_config;
 	engine->device_pause = rcar_dmac_chan_pause;
 	engine->device_terminate_all = rcar_dmac_chan_terminate_all;
+	engine->device_synchronize = rcar_dmac_synchronize;
 	engine->device_tx_status = rcar_dmac_tx_status;
 	engine->device_issue_pending = rcar_dmac_issue_pending;