pinctrl: samsung: Fixes samsung_gpio_direction_in/output releated with spinlock

PATCH Superseded Youngmin Nam 2 participants 3 messages Jan 18, 2016 – Jan 24, 2016

Subsystems (3)

Arm Samsung Exynos Pin control Pin controller - Samsung

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Youngmin Nam

author

2016-01-18 15:21 UTC #0 lore raw

PATCH 1/1 pinctrl: samsung: Fixes samsung_gpio_direction_in/output releated with spinlock

Previously, samsung_gpio_drection_in/output function were not covered with one spinlock.

For example, samsung_gpio_direction_output function consists of two functions.
1. samsung_gpio_set
2. samsung_gpio_set_direction

When 2 CPUs try to control the same gpio pin heavily, (situation like i2c control with gpio emulation) This situation can cause below problem.

CPU 0                                   | CPU1
                                        |
samsung_gpio_direction_output           |
   samsung_gpio_set(pin A as 1)         | samsung_gpio_direction_output
                                        |    samsung_gpio_set(pin A as 0)
   samsung_gpio_set_direction           |
                                        |    samsung_gpio_set_direction

The initial value of pin A will be set as 0 while we wanted to set pin A as 1.

This patch modifies samsung_gpio_direction_in/output function to be done in one spinlock to fix race condition.

Additionally, gpio set callback was changed with samsung_gpio_set_value to implement gpio set callback with spinlock using samsung_gpio_set.

Signed-off-by Youngmin Nam <[email protected]>

---
 drivers/pinctrl/samsung/pinctrl-samsung.c | 38 ++++++++++++++++++++++---------
 1 file changed, 27 insertions(+), 11 deletions(-)

drivers/pinctrl/samsung/pinctrl-samsung.c +27 ~~-11~~

index 48294e7..a25f6f6 100644
@@ -524,20 +524,26 @@ static void samsung_gpio_set(struct gpio_chip *gc, unsigned offset, int value)
 {
 	struct samsung_pin_bank *bank = gc_to_pin_bank(gc);
 	const struct samsung_pin_bank_type *type = bank->type;
-	unsigned long flags;
 	void __iomem *reg;
 	u32 data;
 
 	reg = bank->drvdata->virt_base + bank->pctl_offset;
 
-	spin_lock_irqsave(&bank->slock, flags);
-
 	data = readl(reg + type->reg_offset[PINCFG_TYPE_DAT]);
 	data &= ~(1 << offset);
 	if (value)
 		data |= 1 << offset;
 	writel(data, reg + type->reg_offset[PINCFG_TYPE_DAT]);
+}
+
+static void samsung_gpio_set_value(struct gpio_chip *gc,
+					  unsigned offset, int value)
+{
+	struct samsung_pin_bank *bank = gc_to_pin_bank(gc);
+	unsigned long flags;
 
+	spin_lock_irqsave(&bank->slock, flags);
+	samsung_gpio_set(gc, offset, value);
 	spin_unlock_irqrestore(&bank->slock, flags);
 }

@@ -569,7 +575,6 @@ static int samsung_gpio_set_direction(struct gpio_chip *gc,
 	struct samsung_pinctrl_drv_data *drvdata;
 	void __iomem *reg;
 	u32 data, mask, shift;
-	unsigned long flags;
 
 	bank = gc_to_pin_bank(gc);
 	type = bank->type;

@@ -586,31 +591,42 @@ static int samsung_gpio_set_direction(struct gpio_chip *gc,
 		reg += 4;
 	}
 
-	spin_lock_irqsave(&bank->slock, flags);
-
 	data = readl(reg);
 	data &= ~(mask << shift);
 	if (!input)
 		data |= FUNC_OUTPUT << shift;
 	writel(data, reg);
 
-	spin_unlock_irqrestore(&bank->slock, flags);
-
 	return 0;
 }
 
 /* gpiolib gpio_direction_input callback function. */
 static int samsung_gpio_direction_input(struct gpio_chip *gc, unsigned offset)
 {
-	return samsung_gpio_set_direction(gc, offset, true);
+	struct samsung_pin_bank *bank = gc_to_pin_bank(gc);
+	unsigned long flags;
+	int ret;
+
+	spin_lock_irqsave(&bank->slock, flags);
+	ret = samsung_gpio_set_direction(gc, offset, true);
+	spin_unlock_irqrestore(&bank->slock, flags);
+	return ret;
 }
 
 /* gpiolib gpio_direction_output callback function. */
 static int samsung_gpio_direction_output(struct gpio_chip *gc, unsigned offset,
 							int value)
 {
+	struct samsung_pin_bank *bank = gc_to_pin_bank(gc);
+	unsigned long flags;
+	int ret;
+
+	spin_lock_irqsave(&bank->slock, flags);
 	samsung_gpio_set(gc, offset, value);
-	return samsung_gpio_set_direction(gc, offset, false);
+	ret = samsung_gpio_set_direction(gc, offset, false);
+	spin_unlock_irqrestore(&bank->slock, flags);
+
+	return ret;
 }
 
 /*

@@ -891,7 +907,7 @@ static int samsung_pinctrl_register(struct platform_device *pdev,
 static const struct gpio_chip samsung_gpiolib_chip = {
 	.request = gpiochip_generic_request,
 	.free = gpiochip_generic_free,
-	.set = samsung_gpio_set,
+	.set = samsung_gpio_set_value,
 	.get = samsung_gpio_get,
 	.direction_input = samsung_gpio_direction_input,
 	.direction_output = samsung_gpio_direction_output,

Signature · 1 line

2.7.0.25.gfc10eb5

Tomasz Figa

2016-01-22 04:27 UTC #1 lore raw

Hi Youngmin,

2016-01-19 0:21 GMT+09:00 Youngmin Nam <[email protected]>:

Quoted 3 lines

Previously, samsung_gpio_drection_in/output function were not covered with one spinlock.

Thanks for the patch, nice catch. One nitpick inline, though.

Quoted 3 lines

For example, samsung_gpio_direction_output function consists of two functions.
1. samsung_gpio_set
2. samsung_gpio_set_direction

[snip]

drivers/pinctrl/samsung/pinctrl-samsung.c static void samsung_gpio_set(struct gpio_chip *gc, unsigned offset, int value)

Quoted 3 lines

drivers/pinctrl/samsung/pinctrl-samsung.c +0 -0
@@ -524,20 +524,26 @@ static void samsung_gpio_set(struct gpio_chip *gc, unsigned offset, int value)

Can we, for consistency purposes, rename this function to samsung_gpio_set_value() and keep the one that does locking as samsung_gpio_set()?

This way we would match the gpio_chip op name (.set) and also have both functions with the same name template (set_value and set_direction) follow the same semantics of not doing any locking.

Also adding a comment above the new samsung_gpio_set_value() and existing samsung_gpio_set_direction() that they have to be called with bank->slock held would be helpful to avoid similar bugs in the future.

Best regards,
Tomasz

Youngmin Nam

author

2016-01-24 05:23 UTC #2 lore raw

Hi Tomasz,

Thank you for your review.
I will update my patch applying your review and will resend.

Best regards,
Youngmin

Quoted 32 lines · Tomasz Figa

Hi Youngmin,
2016-01-19 0:21 GMT+09:00 Youngmin Nam <[email protected]>:
Quoted 3 lines
Previously, samsung_gpio_drection_in/output function were not covered with one spinlock.
Thanks for the patch, nice catch. One nitpick inline, though.
Quoted 3 lines
For example, samsung_gpio_direction_output function consists of two functions.
1. samsung_gpio_set
2. samsung_gpio_set_direction
[snip]
drivers/pinctrl/samsung/pinctrl-samsung.c static void samsung_gpio_set(struct gpio_chip *gc, unsigned offset, int value)
Quoted 3 lines
drivers/pinctrl/samsung/pinctrl-samsung.c +0 -0
@@ -524,20 +524,26 @@ static void samsung_gpio_set(struct gpio_chip *gc, unsigned offset, int value)
Can we, for consistency purposes, rename this function to samsung_gpio_set_value() and keep the one that does locking as samsung_gpio_set()?
This way we would match the gpio_chip op name (.set) and also have both functions with the same name template (set_value and set_direction) follow the same semantics of not doing any locking.
Also adding a comment above the new samsung_gpio_set_value() and existing samsung_gpio_set_direction() that they have to be called with bank->slock held would be helpful to avoid similar bugs in the future.
Best regards,
Tomasz