[PATCH v2] pinctrl: stm32: program the EXTI mux from .alloc instead of .activate

[Ju Nan <junan76@163.com>]

stm32_gpio_domain_activate() writes the EXTI interrupt multiplexer
through a regmap obtained from the generic syscon driver. The irq core
calls .activate from __setup_irq() with the raw desc->lock held, so this
happens in a raw atomic section. regmap-mmio sets fast_io, and syscon
does not ask for a raw spinlock, so the regmap is protected by a
spinlock_t. On PREEMPT_RT that is a sleeping lock, which must not be
taken there. lockdep reports it as soon as a GPIO interrupt is
requested:

  BUG: Invalid wait context
  6.17.0 #4 Not tainted
  -----------------------------
  kworker/u8:0/12 is trying to lock:
  (&syscon_config)->lock){....}-{3:3}, at: regmap_lock_spinlock
  other info that might help us debug this:
  6 locks held by kworker/u8:0/12:
   #5: (&irq_desc_lock_class){-...}-{2:2}, at: __setup_irq
  stack backtrace:
   regmap_lock_spinlock
   regmap_field_update_bits_base
   stm32_gpio_domain_activate
   irq_domain_activate_irq
   __setup_irq
   request_threaded_irq

The driver was already aware of running in atomic context there: it uses
the _in_atomic() hwspinlock primitives around the very same access. The
syscon lock is the one lock in that section it does not control.

Program the mux from .alloc instead, which runs in a sleepable context.
That callback already owns this resource: it reserves the mux line in
pctl->irqmux_map under irqmux_lock, so writing the value it just claimed
is a natural fit, and the value only depends on the bank.

Nothing requires the mux to be reprogrammed at interrupt startup time:
the domain has no .deactivate, .free() only releases the irqmux_map bit
without touching the registers, and the resume path reprograms the mux
itself in stm32_pinctrl_restore_gpio_regs().

While moving the code, release the mux reservation when the hwspinlock
cannot be taken, which the .activate callback had no way of doing.

Reported-by: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Closes: https://lore.kernel.org/all/20220202174430.pf37tt6lua2op3gc@pengutronix.de/
Signed-off-by: Ju Nan <junan76@163.com>
---
Changes in v2:

- remove stm32_gpio_domain_activate callback
- program mux register in stm32_gpio_domain_alloc instead

v1: https://lore.kernel.org/all/20260803061718.43210-1-junan76@163.com/
---
 drivers/pinctrl/stm32/pinctrl-stm32.c | 53 ++++++++++++++-------------
 1 file changed, 28 insertions(+), 25 deletions(-)

diff --git a/drivers/pinctrl/stm32/pinctrl-stm32.c b/drivers/pinctrl/stm32/pinctrl-stm32.c
index 6a99708a5a23..4332ac93a6ff 100644
--- a/drivers/pinctrl/stm32/pinctrl-stm32.c
+++ b/drivers/pinctrl/stm32/pinctrl-stm32.c
@@ -600,30 +600,6 @@ static int stm32_gpio_domain_translate(struct irq_domain *d,
 	return 0;
 }
 
-static int stm32_gpio_domain_activate(struct irq_domain *d,
-				      struct irq_data *irq_data, bool reserve)
-{
-	struct stm32_gpio_bank *bank = d->host_data;
-	struct stm32_pinctrl *pctl = dev_get_drvdata(bank->gpio_chip.parent);
-	int ret = 0;
-
-	if (pctl->hwlock) {
-		ret = hwspin_lock_timeout_in_atomic(pctl->hwlock,
-						    HWSPNLCK_TIMEOUT);
-		if (ret) {
-			dev_err(pctl->dev, "Can't get hwspinlock\n");
-			return ret;
-		}
-	}
-
-	regmap_field_write(pctl->irqmux[irq_data->hwirq], bank->bank_ioport_nr);
-
-	if (pctl->hwlock)
-		hwspin_unlock_in_atomic(pctl->hwlock);
-
-	return ret;
-}
-
 static int stm32_gpio_domain_alloc(struct irq_domain *d,
 				   unsigned int virq,
 				   unsigned int nr_irqs, void *data)
@@ -653,6 +629,27 @@ static int stm32_gpio_domain_alloc(struct irq_domain *d,
 	if (ret)
 		return ret;
 
+	/*
+	 * Now that the line is reserved, point its mux at this bank. Doing it
+	 * here rather than from .activate() keeps the access out of the raw
+	 * atomic section the irq core runs .activate() in; nothing needs it to
+	 * be reprogrammed at startup time, and the resume path rewrites it on
+	 * its own.
+	 */
+	if (pctl->hwlock) {
+		ret = hwspin_lock_timeout_in_atomic(pctl->hwlock,
+						    HWSPNLCK_TIMEOUT);
+		if (ret) {
+			dev_err(pctl->dev, "Can't get hwspinlock\n");
+			goto err_free_mux;
+		}
+	}
+
+	regmap_field_write(pctl->irqmux[hwirq], bank->bank_ioport_nr);
+
+	if (pctl->hwlock)
+		hwspin_unlock_in_atomic(pctl->hwlock);
+
 	parent_fwspec.fwnode = d->parent->fwnode;
 	parent_fwspec.param_count = 2;
 	parent_fwspec.param[0] = fwspec->param[0];
@@ -662,6 +659,13 @@ static int stm32_gpio_domain_alloc(struct irq_domain *d,
 				      bank);
 
 	return irq_domain_alloc_irqs_parent(d, virq, nr_irqs, &parent_fwspec);
+
+err_free_mux:
+	spin_lock_irqsave(&pctl->irqmux_lock, flags);
+	pctl->irqmux_map &= ~BIT(hwirq);
+	spin_unlock_irqrestore(&pctl->irqmux_lock, flags);
+
+	return ret;
 }
 
 static void stm32_gpio_domain_free(struct irq_domain *d, unsigned int virq,
@@ -683,7 +687,6 @@ static const struct irq_domain_ops stm32_gpio_domain_ops = {
 	.translate	= stm32_gpio_domain_translate,
 	.alloc		= stm32_gpio_domain_alloc,
 	.free		= stm32_gpio_domain_free,
-	.activate	= stm32_gpio_domain_activate,
 };
 
 /* Pinctrl functions */
-- 
2.55.0