[PATCH-next,07/20] gpio: gpio-omap: simplify omap_gpio_get_direction()

Message ID 20190610171103.30903-8-grygorii.strashko@ti.com
State New
Headers show
Series
  • gpio: gpio-omap: set of fixes and big clean-up
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Commit Message

Grygorii Strashko June 10, 2019, 5:10 p.m.
From: Russell King <rmk+kernel@armlinux.org.uk>


Architectures are single-copy atomic, which means that simply reading
a register is an inherently atomic operation.  There is no need to
take a spinlock here.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>

---
 drivers/gpio/gpio-omap.c | 13 +++----------
 1 file changed, 3 insertions(+), 10 deletions(-)

-- 
2.17.1

Comments

Linus Walleij June 12, 2019, 8:47 a.m. | #1
On Mon, Jun 10, 2019 at 7:12 PM Grygorii Strashko
<grygorii.strashko@ti.com> wrote:

> From: Russell King <rmk+kernel@armlinux.org.uk>

>

> Architectures are single-copy atomic, which means that simply reading

> a register is an inherently atomic operation.  There is no need to

> take a spinlock here.

>

> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

> Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>


Patch applied.

This makes me wonder how many more instances we have
of this kind of mistake in the kernel :/ I guess it is mostly
harmless but it sure makes for massive code complexity.

I would sure like e.g. drivers/gpio/gpio-mmio.c to avoid
taking locks on architectures where this is not a problem
given it is used on a plethora of architectures.

Yours,
Linus Walleij

Patch

diff --git a/drivers/gpio/gpio-omap.c b/drivers/gpio/gpio-omap.c
index cc320d09d074..44a4287cce9e 100644
--- a/drivers/gpio/gpio-omap.c
+++ b/drivers/gpio/gpio-omap.c
@@ -953,17 +953,10 @@  static void omap_gpio_free(struct gpio_chip *chip, unsigned offset)
 
 static int omap_gpio_get_direction(struct gpio_chip *chip, unsigned offset)
 {
-	struct gpio_bank *bank;
-	unsigned long flags;
-	void __iomem *reg;
-	int dir;
+	struct gpio_bank *bank = gpiochip_get_data(chip);
 
-	bank = gpiochip_get_data(chip);
-	reg = bank->base + bank->regs->direction;
-	raw_spin_lock_irqsave(&bank->lock, flags);
-	dir = !!(readl_relaxed(reg) & BIT(offset));
-	raw_spin_unlock_irqrestore(&bank->lock, flags);
-	return dir;
+	return !!(readl_relaxed(bank->base + bank->regs->direction) &
+		  BIT(offset));
 }
 
 static int omap_gpio_input(struct gpio_chip *chip, unsigned offset)