[PATCH v7 3/4] gpio: mxc: fix wakeup_pads bit operations

[Peng Fan (OSS)]

From: Peng Fan <peng.fan at nxp.com>

gpio_set_wake_irq() can be called concurrently for different pins on
the same port. The writer-vs-writer race is the concern: two concurrent
gpio_set_wake_irq() calls for different pins on the same port both do
a non-atomic read-modify-write on the same wakeup_pads word. The old
|= and &= compile to separate load/modify/store instructions that can
interleave, losing one CPU's update.

assign_bit() uses an atomic RMW instruction, so concurrent writers to
different bits in the same word are safe.

The reader side (for_each_set_bit in noirq_suspend, wakeup_pads > 0)
runs in noirq context where no concurrent writer can execute, so
reader atomicity is not needed.

wakeup_pads is a u32, while assign_bit() operates on unsigned long
pointers. On 64-bit platforms, this causes an 8-byte read-modify-write
on a 4-byte field, corrupting the adjacent is_pad_wakeup. So change
wakeup_pads to unsigned long and reorder to avoid wasting words.

And fix the enable/disable path unconditionally sets/clears the
wakeup_pads bit even when enable_irq_wake()/disable_irq_wake() fails.
Only update the bit on success.

Fixes: f60c9eac54af ("gpio: mxc: enable pad wakeup on i.MX8x platforms")
Assisted-by: LLM
Reviewed-by: Frank Li <Frank.Li at nxp.com>
Signed-off-by: Peng Fan <peng.fan at nxp.com>
---
 drivers/gpio/gpio-mxc.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/gpio/gpio-mxc.c b/drivers/gpio/gpio-mxc.c
index 7e17d7668980..e3a80f17d041 100644
--- a/drivers/gpio/gpio-mxc.c
+++ b/drivers/gpio/gpio-mxc.c
@@ -72,8 +72,8 @@ struct mxc_gpio_port {
 	unsigned long both_edges;
 	struct mxc_gpio_reg_saved gpio_saved_reg;
 	bool power_off;
-	u32 wakeup_pads;
 	bool is_pad_wakeup;
+	unsigned long wakeup_pads;
 	u32 pad_type[32];
 	const struct mxc_gpio_hwdata *hwdata;
 };
@@ -331,16 +331,18 @@ static int gpio_set_wake_irq(struct irq_data *d, u32 enable)
 			ret = enable_irq_wake(port->irq_high);
 		else
 			ret = enable_irq_wake(port->irq);
-		port->wakeup_pads |= BIT(gpio_idx);
 	} else {
 		if (port->irq_high && (gpio_idx >= 16))
 			ret = disable_irq_wake(port->irq_high);
 		else
 			ret = disable_irq_wake(port->irq);
-		port->wakeup_pads &= ~BIT(gpio_idx);
 	}
+	if (ret)
+		return ret;
 
-	return ret;
+	assign_bit(gpio_idx, &port->wakeup_pads, enable);
+
+	return 0;
 }
 
 static int mxc_gpio_init_gc(struct mxc_gpio_port *port, int irq_base)

-- 
2.51.0