linux-kernel - Re: [PATCH v2 7/9] gpio: 104-idi-48: make use of raw

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Date:   Wed, 22 Mar 2017 08:44:14 -0400
From:   William Breathitt Gray <vilhelm.gray@...il.com>
To:     Julia Cartwright <julia@...com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Alexandre Courbot <gnurou@...il.com>,
        linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
        linux-gpio@...r.kernel.org
Subject: Re: [PATCH v2 7/9] gpio: 104-idi-48: make use of raw_spinlock
 variants

On Tue, Mar 21, 2017 at 05:43:07PM -0500, Julia Cartwright wrote:
>The 104-idi-48 gpio driver currently implements an irq_chip for handling
>interrupts; due to how irq_chip handling is done, it's necessary for the
>irq_chip methods to be invoked from hardirq context, even on a a
>real-time kernel.  Because the spinlock_t type becomes a "sleeping"
>spinlock w/ RT kernels, it is not suitable to be used with irq_chips.
>
>A quick audit of the operations under the lock reveal that they do only
>minimal, bounded work, and are therefore safe to do under a raw spinlock.
>
>Signed-off-by: Julia Cartwright <julia@...com>

Hi Julia,

This driver also uses a second spinlock_t, called ack_lock, to prevent
reentrance into the idi_48_irq_handler function. Should ack_lock also be
implemented as a raw_spinlock_t?

Thanks,

William Breathitt Gray

>---
>New patch as of v2 of series.
>
> drivers/gpio/gpio-104-idi-48.c | 18 ++++++++++--------
> 1 file changed, 10 insertions(+), 8 deletions(-)
>
>diff --git a/drivers/gpio/gpio-104-idi-48.c b/drivers/gpio/gpio-104-idi-48.c
>index 568375a7ebc2..337c048168d8 100644
>--- a/drivers/gpio/gpio-104-idi-48.c
>+++ b/drivers/gpio/gpio-104-idi-48.c
>@@ -51,7 +51,7 @@ MODULE_PARM_DESC(irq, "ACCES 104-IDI-48 interrupt line numbers");
>  */
> struct idi_48_gpio {
> 	struct gpio_chip chip;
>-	spinlock_t lock;
>+	raw_spinlock_t lock;
> 	spinlock_t ack_lock;
> 	unsigned char irq_mask[6];
> 	unsigned base;
>@@ -112,11 +112,12 @@ static void idi_48_irq_mask(struct irq_data *data)
> 			if (!idi48gpio->irq_mask[boundary]) {
> 				idi48gpio->cos_enb &= ~BIT(boundary);
> 
>-				spin_lock_irqsave(&idi48gpio->lock, flags);
>+				raw_spin_lock_irqsave(&idi48gpio->lock, flags);
> 
> 				outb(idi48gpio->cos_enb, idi48gpio->base + 7);
> 
>-				spin_unlock_irqrestore(&idi48gpio->lock, flags);
>+				raw_spin_unlock_irqrestore(&idi48gpio->lock,
>+						           flags);
> 			}
> 
> 			return;
>@@ -145,11 +146,12 @@ static void idi_48_irq_unmask(struct irq_data *data)
> 			if (!prev_irq_mask) {
> 				idi48gpio->cos_enb |= BIT(boundary);
> 
>-				spin_lock_irqsave(&idi48gpio->lock, flags);
>+				raw_spin_lock_irqsave(&idi48gpio->lock, flags);
> 
> 				outb(idi48gpio->cos_enb, idi48gpio->base + 7);
> 
>-				spin_unlock_irqrestore(&idi48gpio->lock, flags);
>+				raw_spin_unlock_irqrestore(&idi48gpio->lock,
>+						           flags);
> 			}
> 
> 			return;
>@@ -186,11 +188,11 @@ static irqreturn_t idi_48_irq_handler(int irq, void *dev_id)
> 
> 	spin_lock(&idi48gpio->ack_lock);
> 
>-	spin_lock(&idi48gpio->lock);
>+	raw_spin_lock(&idi48gpio->lock);
> 
> 	cos_status = inb(idi48gpio->base + 7);
> 
>-	spin_unlock(&idi48gpio->lock);
>+	raw_spin_unlock(&idi48gpio->lock);
> 
> 	/* IRQ Status (bit 6) is active low (0 = IRQ generated by device) */
> 	if (cos_status & BIT(6)) {
>@@ -256,7 +258,7 @@ static int idi_48_probe(struct device *dev, unsigned int id)
> 	idi48gpio->chip.get = idi_48_gpio_get;
> 	idi48gpio->base = base[id];
> 
>-	spin_lock_init(&idi48gpio->lock);
>+	raw_spin_lock_init(&idi48gpio->lock);
> 	spin_lock_init(&idi48gpio->ack_lock);
> 
> 	err = devm_gpiochip_add_data(dev, &idi48gpio->chip, idi48gpio);
>-- 
>2.12.0
>