[PATCH] pinctrl: mediatek: common-v1: Use a raw spinlock for the pinctrl regmap

[Ryan Brue]

The EINT irq_chip emulates both-edge interrupts by reading the pin's
level through mtk_gpio_get() and the pinctrl regmap. It does so from its
unmask and set_type callbacks, under the raw irq_desc lock, and from the
chained handler, in hard interrupt context. The regmap comes from syscon
and locks with a spinlock_t, which may sleep on PREEMPT_RT. With
CONFIG_PROVE_LOCKING, the first request of a both-edge EINT prints
"[ BUG: Invalid wait context ]" and turns lockdep off for the rest of
the boot.

Create the regmap for the "mediatek,pctl-regmap" nodes here instead,
with use_raw_spinlock set, and register it with syscon so that other
users of a node, such as the ethernet on MT2701 and MT7623, share its
lock. If the node already has a syscon regmap, keep using it. Select
REGMAP_MMIO, which the driver now uses directly.

Fixes: 3221f40b7631 ("pinctrl: mediatek: emulate GPIO interrupt on both-edges")
Assisted-by: LLM
Signed-off-by: Ryan Brue <ryanbrue.dev@xxxxxxxxx>
---
Found on the Amazon Fire HD 10 (2017), an MT8173 tablet that is not
upstream yet, where usb_extcon_probe() requests the USB ID pin's
both-edge EINT. With this patch lockdep stays on through boot, CPU
hotplug, suspend to RAM, and lid open/close edges on the hall sensor's
both-edge EINT. Only MT8173 was tested. Nothing else uses the node
there, so the -EEXIST fallback was not exercised.

checkpatch warns that the regmap_config should be const. It is copied
per node to set name and max_register, as syscon does.
---
 drivers/pinctrl/mediatek/Kconfig              |  1 +
 drivers/pinctrl/mediatek/pinctrl-mtk-common.c | 59 ++++++++++++++++++++++++++-
 2 files changed, 58 insertions(+), 2 deletions(-)

diff --git a/drivers/pinctrl/mediatek/Kconfig b/drivers/pinctrl/mediatek/Kconfig
index 30ef3dc5dfb1..764256901d6a 100644
--- a/drivers/pinctrl/mediatek/Kconfig
+++ b/drivers/pinctrl/mediatek/Kconfig
@@ -17,6 +17,7 @@ config PINCTRL_MTK
 	select GENERIC_PINCONF
 	select GPIOLIB
 	select EINT_MTK
+	select REGMAP_MMIO
 
 config PINCTRL_MTK_V2
 	tristate
diff --git a/drivers/pinctrl/mediatek/pinctrl-mtk-common.c b/drivers/pinctrl/mediatek/pinctrl-mtk-common.c
index 1a977acd6883..65b1e3096183 100644
--- a/drivers/pinctrl/mediatek/pinctrl-mtk-common.c
+++ b/drivers/pinctrl/mediatek/pinctrl-mtk-common.c
@@ -9,6 +9,7 @@
 #include <linux/gpio/driver.h>
 #include <linux/module.h>
 #include <linux/of.h>
+#include <linux/of_address.h>
 #include <linux/of_irq.h>
 #include <linux/pinctrl/consumer.h>
 #include <linux/pinctrl/machine.h>
@@ -1057,6 +1058,60 @@ static int mtk_eint_init(struct mtk_pinctrl *pctl, struct platform_device *pdev)
 	return mtk_eint_do_init(pctl->eint, NULL);
 }
 
+static const struct regmap_config mtk_pctrl_regmap_config = {
+	.reg_bits = 32,
+	.val_bits = 32,
+	.reg_stride = 4,
+	.use_raw_spinlock = true,
+};
+
+/*
+ * The EINT irq_chip reads a pin's level through this regmap from callbacks
+ * that run under the raw irq_desc lock, so the regmap has to use a raw
+ * spinlock too, which syscon's own does not. Register one with syscon for the
+ * node instead, so that any other user of the node shares its lock.
+ */
+static struct regmap *mtk_pctrl_syscon_regmap(struct device_node *np)
+{
+	struct regmap_config config = mtk_pctrl_regmap_config;
+	struct regmap *regmap;
+	struct resource res;
+	void __iomem *base;
+	int ret;
+
+	ret = of_address_to_resource(np, 0, &res);
+	if (ret)
+		return ERR_PTR(ret);
+
+	base = ioremap(res.start, resource_size(&res));
+	if (!base)
+		return ERR_PTR(-ENOMEM);
+
+	config.name = kasprintf(GFP_KERNEL, "%pOFn@%pa", np, &res.start);
+	if (!config.name) {
+		iounmap(base);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	config.max_register = resource_size(&res) - config.reg_stride;
+	regmap = regmap_init_mmio(NULL, base, &config);
+	kfree(config.name);
+	if (IS_ERR(regmap)) {
+		iounmap(base);
+		return regmap;
+	}
+
+	ret = of_syscon_register_regmap(np, regmap);
+	if (ret) {
+		regmap_exit(regmap);
+		iounmap(base);
+		/* An earlier probe, or another user of the node, got there first. */
+		return ret == -EEXIST ? syscon_node_to_regmap(np) : ERR_PTR(ret);
+	}
+
+	return regmap;
+}
+
 /* This is used as a common probe function */
 int mtk_pctrl_init(struct platform_device *pdev,
 		const struct mtk_pinctrl_devdata *data,
@@ -1076,7 +1131,7 @@ int mtk_pctrl_init(struct platform_device *pdev,
 
 	node = of_parse_phandle(np, "mediatek,pctl-regmap", 0);
 	if (node) {
-		pctl->regmap1 = syscon_node_to_regmap(node);
+		pctl->regmap1 = mtk_pctrl_syscon_regmap(node);
 		of_node_put(node);
 		if (IS_ERR(pctl->regmap1))
 			return PTR_ERR(pctl->regmap1);
@@ -1089,7 +1144,7 @@ int mtk_pctrl_init(struct platform_device *pdev,
 	/* Only 8135 has two base addr, other SoCs have only one. */
 	node = of_parse_phandle(np, "mediatek,pctl-regmap", 1);
 	if (node) {
-		pctl->regmap2 = syscon_node_to_regmap(node);
+		pctl->regmap2 = mtk_pctrl_syscon_regmap(node);
 		of_node_put(node);
 		if (IS_ERR(pctl->regmap2))
 			return PTR_ERR(pctl->regmap2);

---
base-commit: 72d3fcf802c45d00b300f25b848a93c3a2bd7c7e
change-id: 20260925-rbrue-suez-upstreaming-mtk-pinctrl-raw-regmap-154d6225b977

Best regards,
--  
Ryan Brue <ryanbrue.dev@xxxxxxxxx>