[PATCH AUTOSEL 6.16-5.4] pinctrl: stm32: Manage irq affinity settings

[Sasha Levin]

From: Cheick Traore <cheick.traore at foss.st.com>

[ Upstream commit 4c5cc2f65386e22166ce006efe515c667aa075e4 ]

Trying to set the affinity of the interrupts associated to stm32
pinctrl results in a write error.

Fill struct irq_chip::irq_set_affinity to use the default helper
function.

Signed-off-by: Cheick Traore <cheick.traore at foss.st.com>
Signed-off-by: Antonio Borneo <antonio.borneo at foss.st.com>
Link: https://lore.kernel.org/20250610143042.295376-3-antonio.borneo@foss.st.com
Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
Signed-off-by: Sasha Levin <sashal at kernel.org>
---

LLM Generated explanations, may be completely bogus:

Based on my analysis, here's my assessment:

**Backport Status: YES**

This commit should be backported to stable kernel trees for the
following reasons:

1. **Fixes a real bug**: The commit message explicitly states "Trying to
   set the affinity of the interrupts associated to stm32 pinctrl
   results in a write error." This is a functional bug that affects
   users trying to configure IRQ affinity on STM32 platforms.

2. **Small and contained fix**: The change is minimal - just adding a
   single line:
  ```c
  .irq_set_affinity = IS_ENABLED(CONFIG_SMP) ?
  irq_chip_set_affinity_parent : NULL,
  ```
  This is a one-line fix that adds the missing callback to the irq_chip
  structure.

3. **Follows established patterns**: My analysis shows that other
   GPIO/pinctrl drivers already implement this callback in the same way:
   - `drivers/pinctrl/renesas/pinctrl-rzg2l.c`
   - `drivers/gpio/gpio-thunderx.c`
   - `drivers/gpio/gpio-msc313.c`

   The STM32 driver was missing this standard callback that other
similar drivers have.

4. **No architectural changes**: This is purely a bug fix that enables
   existing kernel functionality (IRQ affinity setting) to work
   properly. It doesn't introduce new features or change any
   architecture.

5. **Minimal regression risk**: The fix uses the standard
   `irq_chip_set_affinity_parent` helper function that's already well-
   tested in the kernel. The conditional compilation with
   `IS_ENABLED(CONFIG_SMP)` ensures it's only enabled on SMP systems
   where it's relevant.

6. **Related to known issues**: My search found related commits like
   `3e17683ff4a8` ("irqchip/stm32-exti: Fix irq_set_affinity return
   value") showing that the STM32 platform has had IRQ affinity issues
   that needed fixing.

7. **Clear user impact**: Without this fix, users cannot set IRQ
   affinity for GPIO interrupts on STM32 platforms, which can impact
   system performance optimization and interrupt load balancing on
   multi-core STM32 systems.

The commit meets all the stable tree criteria: it fixes an important
bug, is small and self-contained, has minimal risk, and doesn't
introduce new functionality. This is exactly the type of fix that should
be backported to ensure stable kernels have proper functionality.

 drivers/pinctrl/stm32/pinctrl-stm32.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/pinctrl/stm32/pinctrl-stm32.c b/drivers/pinctrl/stm32/pinctrl-stm32.c
index ba49d48c3a1d..e6ad63df82b7 100644
--- a/drivers/pinctrl/stm32/pinctrl-stm32.c
+++ b/drivers/pinctrl/stm32/pinctrl-stm32.c
@@ -411,6 +411,7 @@ static struct irq_chip stm32_gpio_irq_chip = {
 	.irq_set_wake	= irq_chip_set_wake_parent,
 	.irq_request_resources = stm32_gpio_irq_request_resources,
 	.irq_release_resources = stm32_gpio_irq_release_resources,
+	.irq_set_affinity = IS_ENABLED(CONFIG_SMP) ? irq_chip_set_affinity_parent : NULL,
 };
 
 static int stm32_gpio_domain_translate(struct irq_domain *d,
-- 
2.39.5