[PATCH v2 8/9] mailbox: imx: Don't force-thread the primary handler

[Sebastian Andrzej Siewior]

The primary interrupt handler (imx_mu_isr()) no longer invokes any
callbacks it only masks the interrupt source and returns. In a
forced-threaded environment the IRQ-core will force-thread the primary
handler which can be avoided.

The primary handler uses a spinlock_t to protect the RMW operation in
imx_mu_xcr_rmw() - nothing that may introduce long latencies.

The lock can be turned into a raw_spinlock_t and then the primary
handler can run in hardirq context even on PREEMPT_RT skipping one
thread.

Make struct imx_mu_priv::xcr_lock a raw_spinlock_t and skip
force-threading the primrary handler by marking it IRQF_NO_THREAD.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
---
 drivers/mailbox/imx-mailbox.c | 19 +++++++------------
 1 file changed, 7 insertions(+), 12 deletions(-)

diff --git a/drivers/mailbox/imx-mailbox.c b/drivers/mailbox/imx-mailbox.c
index f0a14449652f1..f3de47908e00f 100644
--- a/drivers/mailbox/imx-mailbox.c
+++ b/drivers/mailbox/imx-mailbox.c
@@ -88,7 +88,7 @@ struct imx_mu_priv {
 	struct device		*dev;
 	void __iomem		*base;
 	void			*msg;
-	spinlock_t		xcr_lock; /* control register lock */
+	raw_spinlock_t		xcr_lock; /* control register lock */
 
 	struct mbox_controller	mbox;
 	struct mbox_chan	mbox_chans[IMX_MU_CHANS];
@@ -208,15 +208,14 @@ static int imx_mu_rx_waiting_read(struct imx_mu_priv *priv, u32 *val, u32 idx)
 
 static u32 imx_mu_xcr_rmw(struct imx_mu_priv *priv, enum imx_mu_xcr type, u32 set, u32 clr)
 {
-	unsigned long flags;
 	u32 val;
 
-	spin_lock_irqsave(&priv->xcr_lock, flags);
+	guard(raw_spinlock_irqsave)(&priv->xcr_lock);
+
 	val = imx_mu_read(priv, priv->dcfg->xCR[type]);
 	val &= ~clr;
 	val |= set;
 	imx_mu_write(priv, val, priv->dcfg->xCR[type]);
-	spin_unlock_irqrestore(&priv->xcr_lock, flags);
 
 	return val;
 }
@@ -224,31 +223,27 @@ static u32 imx_mu_xcr_rmw(struct imx_mu_priv *priv, enum imx_mu_xcr type, u32 se
 static void imx_mu_xcr_clr_shut(struct imx_mu_priv *priv, struct imx_mu_con_priv *cp,
 				enum imx_mu_xcr type, u32 clr)
 {
-	unsigned long flags;
 	u32 val;
 
-	spin_lock_irqsave(&priv->xcr_lock, flags);
+	guard(raw_spinlock_irqsave)(&priv->xcr_lock);
 	cp->shutdown = true;
 
 	val = imx_mu_read(priv, priv->dcfg->xCR[type]);
 	val &= ~clr;
 	imx_mu_write(priv, val, priv->dcfg->xCR[type]);
-	spin_unlock_irqrestore(&priv->xcr_lock, flags);
 }
 
 static void imx_mu_xcr_set_act(struct imx_mu_priv *priv, struct imx_mu_con_priv *cp,
 			       enum imx_mu_xcr type, u32 set)
 {
-	unsigned long flags;
 	u32 val;
 
-	spin_lock_irqsave(&priv->xcr_lock, flags);
+	guard(raw_spinlock_irqsave)(&priv->xcr_lock);
 	if (!cp->shutdown) {
 		val = imx_mu_read(priv, priv->dcfg->xCR[type]);
 		val |= set;
 		imx_mu_write(priv, val, priv->dcfg->xCR[type]);
 	}
-	spin_unlock_irqrestore(&priv->xcr_lock, flags);
 }
 
 static int imx_mu_generic_tx(struct imx_mu_priv *priv,
@@ -649,7 +644,7 @@ static int imx_mu_startup(struct mbox_chan *chan)
 {
 	struct imx_mu_priv *priv = to_imx_mu_priv(chan->mbox);
 	struct imx_mu_con_priv *cp = chan->con_priv;
-	unsigned long irq_flag = 0;
+	unsigned long irq_flag = IRQF_NO_THREAD;
 	int ret;
 
 	pm_runtime_get_sync(priv->dev);
@@ -997,7 +992,7 @@ static int imx_mu_probe(struct platform_device *pdev)
 		goto disable_clk;
 	}
 
-	spin_lock_init(&priv->xcr_lock);
+	raw_spin_lock_init(&priv->xcr_lock);
 
 	priv->mbox.dev = dev;
 	priv->mbox.ops = &imx_mu_ops;

-- 
2.53.0