[PATCH 1/3] mailbox: sprd: Introduce refcnt when clients requests/free channels

[Orson Zhai <orsonzhai@gmail.com>]

From: Orson Zhai <orson.zhai@unisoc.com>

Unisoc mailbox has no way to be enabled/disabled for any single channel.
They can only be set to startup or shutdown as a whole device at same time.

Add a variable to count references to avoid mailbox FIFO being reset
unexpectedly when clients are requesting or freeing channels.

Also add a lock to dismiss possible conflicts from register r/w in
different startup or shutdown threads.

Fixes: ca27fc26cd22 ("mailbox: sprd: Add Spreadtrum mailbox driver")
Signed-off-by: Orson Zhai <orson.zhai@unisoc.com>
---
 drivers/mailbox/sprd-mailbox.c | 38 +++++++++++++++++++++++++-------------
 1 file changed, 25 insertions(+), 13 deletions(-)

diff --git a/drivers/mailbox/sprd-mailbox.c b/drivers/mailbox/sprd-mailbox.c
index f6fab24..e606f52 100644
--- a/drivers/mailbox/sprd-mailbox.c
+++ b/drivers/mailbox/sprd-mailbox.c
@@ -60,6 +60,8 @@ struct sprd_mbox_priv {
 	struct clk		*clk;
 	u32			outbox_fifo_depth;
 
+	struct mutex		lock;
+	u32			refcnt;
 	struct mbox_chan	chan[SPRD_MBOX_CHAN_MAX];
 };
 
@@ -215,18 +217,22 @@ static int sprd_mbox_startup(struct mbox_chan *chan)
 	struct sprd_mbox_priv *priv = to_sprd_mbox_priv(chan->mbox);
 	u32 val;
 
-	/* Select outbox FIFO mode and reset the outbox FIFO status */
-	writel(0x0, priv->outbox_base + SPRD_MBOX_FIFO_RST);
+	mutex_lock(&priv->lock);
+	if (priv->refcnt++ == 0) {
+		/* Select outbox FIFO mode and reset the outbox FIFO status */
+		writel(0x0, priv->outbox_base + SPRD_MBOX_FIFO_RST);
 
-	/* Enable inbox FIFO overflow and delivery interrupt */
-	val = readl(priv->inbox_base + SPRD_MBOX_IRQ_MSK);
-	val &= ~(SPRD_INBOX_FIFO_OVERFLOW_IRQ | SPRD_INBOX_FIFO_DELIVER_IRQ);
-	writel(val, priv->inbox_base + SPRD_MBOX_IRQ_MSK);
+		/* Enable inbox FIFO overflow and delivery interrupt */
+		val = readl(priv->inbox_base + SPRD_MBOX_IRQ_MSK);
+		val &= ~(SPRD_INBOX_FIFO_OVERFLOW_IRQ | SPRD_INBOX_FIFO_DELIVER_IRQ);
+		writel(val, priv->inbox_base + SPRD_MBOX_IRQ_MSK);
 
-	/* Enable outbox FIFO not empty interrupt */
-	val = readl(priv->outbox_base + SPRD_MBOX_IRQ_MSK);
-	val &= ~SPRD_OUTBOX_FIFO_NOT_EMPTY_IRQ;
-	writel(val, priv->outbox_base + SPRD_MBOX_IRQ_MSK);
+		/* Enable outbox FIFO not empty interrupt */
+		val = readl(priv->outbox_base + SPRD_MBOX_IRQ_MSK);
+		val &= ~SPRD_OUTBOX_FIFO_NOT_EMPTY_IRQ;
+		writel(val, priv->outbox_base + SPRD_MBOX_IRQ_MSK);
+	}
+	mutex_unlock(&priv->lock);
 
 	return 0;
 }
@@ -235,9 +241,13 @@ static void sprd_mbox_shutdown(struct mbox_chan *chan)
 {
 	struct sprd_mbox_priv *priv = to_sprd_mbox_priv(chan->mbox);
 
-	/* Disable inbox & outbox interrupt */
-	writel(SPRD_INBOX_FIFO_IRQ_MASK, priv->inbox_base + SPRD_MBOX_IRQ_MSK);
-	writel(SPRD_OUTBOX_FIFO_IRQ_MASK, priv->outbox_base + SPRD_MBOX_IRQ_MSK);
+	mutex_lock(&priv->lock);
+	if (--priv->refcnt == 0) {
+		/* Disable inbox & outbox interrupt */
+		writel(SPRD_INBOX_FIFO_IRQ_MASK, priv->inbox_base + SPRD_MBOX_IRQ_MSK);
+		writel(SPRD_OUTBOX_FIFO_IRQ_MASK, priv->outbox_base + SPRD_MBOX_IRQ_MSK);
+	}
+	mutex_unlock(&priv->lock);
 }
 
 static const struct mbox_chan_ops sprd_mbox_ops = {
@@ -266,6 +276,8 @@ static int sprd_mbox_probe(struct platform_device *pdev)
 		return -ENOMEM;
 
 	priv->dev = dev;
+	priv->refcnt = 0;
+	mutex_init(&priv->lock);
 
 	/*
 	 * The Spreadtrum mailbox uses an inbox to send messages to the target
-- 
2.7.4