irqchip/ls-extirq: Fix invalid wait context by avoiding to use regmap

The irqchip->irq_set_type method is called by __irq_set_trigger() under
the desc->lock raw spinlock.

The ls-extirq implementation, ls_extirq_irq_set_type(), uses an MMIO
regmap created by of_syscon_register(), which uses plain spinlocks
(the kind that are sleepable on RT).

Therefore, this is an invalid locking scheme for which we get a kernel
splat stating just that ("[ BUG: Invalid wait context ]"), because the
context in which the plain spinlock may sleep is atomic due to the raw
spinlock. We need to go raw spinlocks all the way.

Make this driver ioremap its INTPCR register on its own, and stop
relying on syscon to provide a regmap.

Fixes: 0dcd9f87 ("irqchip: Add support for Layerscape external interrupt lines")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
[maz: trimmed down commit log]
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220728144254.175385-1-vladimir.oltean@nxp.com

drivers/irqchip/irq-ls-extirq.c

@@ -6,8 +6,7 @@
 #include <linux/irqchip.h>
 #include <linux/irqdomain.h>
 #include <linux/of.h>
-#include <linux/mfd/syscon.h>
-#include <linux/regmap.h>
+#include <linux/of_address.h>
 #include <linux/slab.h>
 
 #include <dt-bindings/interrupt-controller/arm-gic.h>
@@ -16,13 +15,41 @@
 #define LS1021A_SCFGREVCR 0x200
 
 struct ls_extirq_data {
-	struct regmap		*syscon;
-	u32			intpcr;
+	void __iomem		*intpcr;
+	raw_spinlock_t		lock;
+	bool			big_endian;
 	bool			is_ls1021a_or_ls1043a;
 	u32			nirq;
 	struct irq_fwspec	map[MAXIRQ];
 };
 
+static void ls_extirq_intpcr_rmw(struct ls_extirq_data *priv, u32 mask,
+				 u32 value)
+{
+	u32 intpcr;
+
+	/*
+	 * Serialize concurrent calls to ls_extirq_set_type() from multiple
+	 * IRQ descriptors, making sure the read-modify-write is atomic.
+	 */
+	raw_spin_lock(&priv->lock);
+
+	if (priv->big_endian)
+		intpcr = ioread32be(priv->intpcr);
+	else
+		intpcr = ioread32(priv->intpcr);
+
+	intpcr &= ~mask;
+	intpcr |= value;
+
+	if (priv->big_endian)
+		iowrite32be(intpcr, priv->intpcr);
+	else
+		iowrite32(intpcr, priv->intpcr);
+
+	raw_spin_unlock(&priv->lock);
+}
+
 static int
 ls_extirq_set_type(struct irq_data *data, unsigned int type)
 {
@@ -51,7 +78,8 @@ ls_extirq_set_type(struct irq_data *data, unsigned int type)
 	default:
 		return -EINVAL;
 	}
-	regmap_update_bits(priv->syscon, priv->intpcr, mask, value);
+
+	ls_extirq_intpcr_rmw(priv, mask, value);
 
 	return irq_chip_set_type_parent(data, type);
 }
@@ -143,7 +171,6 @@ ls_extirq_parse_map(struct ls_extirq_data *priv, struct device_node *node)
 static int __init
 ls_extirq_of_init(struct device_node *node, struct device_node *parent)
 {
-
 	struct irq_domain *domain, *parent_domain;
 	struct ls_extirq_data *priv;
 	int ret;
@@ -151,40 +178,52 @@ ls_extirq_of_init(struct device_node *node, struct device_node *parent)
 	parent_domain = irq_find_host(parent);
 	if (!parent_domain) {
 		pr_err("Cannot find parent domain\n");
-		return -ENODEV;
+		ret = -ENODEV;
+		goto err_irq_find_host;
 	}
 
 	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
-	if (!priv)
-		return -ENOMEM;
-
-	priv->syscon = syscon_node_to_regmap(node->parent);
-	if (IS_ERR(priv->syscon)) {
-		ret = PTR_ERR(priv->syscon);
-		pr_err("Failed to lookup parent regmap\n");
-		goto out;
+	if (!priv) {
+		ret = -ENOMEM;
+		goto err_alloc_priv;
 	}
-	ret = of_property_read_u32(node, "reg", &priv->intpcr);
-	if (ret) {
-		pr_err("Missing INTPCR offset value\n");
-		goto out;
+
+	/*
+	 * All extirq OF nodes are under a scfg/syscon node with
+	 * the 'ranges' property
+	 */
+	priv->intpcr = of_iomap(node, 0);
+	if (!priv->intpcr) {
+		pr_err("Cannot ioremap OF node %pOF\n", node);
+		ret = -ENOMEM;
+		goto err_iomap;
 	}
 
 	ret = ls_extirq_parse_map(priv, node);
 	if (ret)
-		goto out;
+		goto err_parse_map;
 
+	priv->big_endian = of_device_is_big_endian(parent);
 	priv->is_ls1021a_or_ls1043a = of_device_is_compatible(node, "fsl,ls1021a-extirq") ||
 				      of_device_is_compatible(node, "fsl,ls1043a-extirq");
+	raw_spin_lock_init(&priv->lock);
 
 	domain = irq_domain_add_hierarchy(parent_domain, 0, priv->nirq, node,
 					  &extirq_domain_ops, priv);
-	if (!domain)
+	if (!domain) {
 		ret = -ENOMEM;
+		goto err_add_hierarchy;
+	}
 
-out:
-	if (ret)
+	return 0;
+
+err_add_hierarchy:
+err_parse_map:
+	iounmap(priv->intpcr);
+err_iomap:
 	kfree(priv);
+err_alloc_priv:
+err_irq_find_host:
 	return ret;
 }