i2c: mux: pca954x: make use of raw_spinlock variants

The pca954x i2c mux driver currently implements an irq_chip for handling
interrupts; due to how irq_chip handling is done, it's necessary for the
irq_chip methods to be invoked from hardirq context, even on a a
real-time kernel.  Because the spinlock_t type becomes a "sleeping"
spinlock w/ RT kernels, it is not suitable to be used with irq_chips.

A quick audit of the operations under the lock reveal that they do only
minimal, bounded work, and are therefore safe to do under a raw spinlock.

Signed-off-by: Julia Cartwright <julia@ni.com>
Signed-off-by: Peter Rosin <peda@axentia.se>

drivers/i2c/muxes/i2c-mux-pca954x.c

@@ -85,7 +85,7 @@ struct pca954x {
 
 	struct irq_domain *irq;
 	unsigned int irq_mask;
-	spinlock_t lock;
+	raw_spinlock_t lock;
 };
 
 /* Provide specs for the PCA954x types we know about */
@@ -264,13 +264,13 @@ static void pca954x_irq_mask(struct irq_data *idata)
 	unsigned int pos = idata->hwirq;
 	unsigned long flags;
 
-	spin_lock_irqsave(&data->lock, flags);
+	raw_spin_lock_irqsave(&data->lock, flags);
 
 	data->irq_mask &= ~BIT(pos);
 	if (!data->irq_mask)
 		disable_irq(data->client->irq);
 
-	spin_unlock_irqrestore(&data->lock, flags);
+	raw_spin_unlock_irqrestore(&data->lock, flags);
 }
 
 static void pca954x_irq_unmask(struct irq_data *idata)
@@ -279,13 +279,13 @@ static void pca954x_irq_unmask(struct irq_data *idata)
 	unsigned int pos = idata->hwirq;
 	unsigned long flags;
 
-	spin_lock_irqsave(&data->lock, flags);
+	raw_spin_lock_irqsave(&data->lock, flags);
 
 	if (!data->irq_mask)
 		enable_irq(data->client->irq);
 	data->irq_mask |= BIT(pos);
 
-	spin_unlock_irqrestore(&data->lock, flags);
+	raw_spin_unlock_irqrestore(&data->lock, flags);
 }
 
 static int pca954x_irq_set_type(struct irq_data *idata, unsigned int type)
@@ -311,7 +311,7 @@ static int pca954x_irq_setup(struct i2c_mux_core *muxc)
 	if (!data->chip->has_irq || client->irq <= 0)
 		return 0;
 
-	spin_lock_init(&data->lock);
+	raw_spin_lock_init(&data->lock);
 
 	data->irq = irq_domain_add_linear(client->dev.of_node,
 					  data->chip->nchans,