[PATCH 2/9] gpio: mxc: fix wakeup_pads bit operations for correctness

[Peng Fan (OSS)]

From: Peng Fan <peng.fan@xxxxxxx>

Replace the open-coded BIT() / mask operations with the atomic
set_bit() / clear_bit() / test_bit() API. Atomic variants are required
because gpio_set_wake_irq() can be called concurrently for different
pins on the same port - irq_set_irq_wake() only holds the per-IRQ
descriptor lock, not a per-port lock, so concurrent modification of
different bits in wakeup_pads is possible.

However wakeup_pads field is typed as u32 but accessed via set_bit() /
clear_bit() / test_bit() which operate 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 field.

Change wakeup_pads from u32 to unsigned long to match the bitops API
width requirements.

Also fix the disable path to only clear the wakeup_pads bit when
disable_irq_wake() succeeds, matching the enable path which already
checks the return value. Previously, a failed disable_irq_wake() would
still clear the bit, causing the driver to lose track of the wakeup
source.

Also fix a latent signed-shift bug: the old (1 << i) expression in
mxc_gpio_set_pad_wakeup() has implementation-defined behavior when
i == 31, since 1 is a signed int.

Fixes: f60c9eac54af ("gpio: mxc: enable pad wakeup on i.MX8x platforms")
Assisted-by: LLM
Signed-off-by: Peng Fan <peng.fan@xxxxxxx>
---
 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 e05f276a50e8..8a755ac1af83 100644
--- a/drivers/gpio/gpio-mxc.c
+++ b/drivers/gpio/gpio-mxc.c
@@ -71,7 +71,7 @@ struct mxc_gpio_port {
 	u32 both_edges;
 	struct mxc_gpio_reg_saved gpio_saved_reg;
 	bool power_off;
-	u32 wakeup_pads;
+	unsigned long wakeup_pads;
 	bool is_pad_wakeup;
 	u32 pad_type[32];
 	const struct mxc_gpio_hwdata *hwdata;
@@ -330,13 +330,15 @@ 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);
+		if (!ret)
+			set_bit(gpio_idx, &port->wakeup_pads);
 	} 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)
+			clear_bit(gpio_idx, &port->wakeup_pads);
 	}
 
 	return ret;
@@ -599,7 +601,7 @@ static bool mxc_gpio_set_pad_wakeup(struct mxc_gpio_port *port, bool enable)
 	};
 
 	for (i = 0; i < 32; i++) {
-		if ((port->wakeup_pads & (1 << i))) {
+		if (test_bit(i, &port->wakeup_pads)) {
 			type = port->pad_type[i];
 			if (enable)
 				config = pad_type_map[type];

-- 
2.51.0