[v2,04/10] i2c: rcar: remove spinlock

Commit Message

Wolfram Sang Nov. 12, 2015, 2:31 p.m. UTC

From: Wolfram Sang <[e-mail]>

After making sure to reinit the HW and clear interrupts in the timeout
case, we know that interrupts are always disabled in the sections
protected by the spinlock. Thus, we can simply remove it which is a
preparation for further refactoring. While here, rename the timeout
variable to time_left which is way more readable.

Signed-off-by: Wolfram Sang <[e-mail]>
---
 drivers/i2c/busses/i2c-rcar.c | 23 ++++-------------------
 1 file changed, 4 insertions(+), 19 deletions(-)

Comments

Sergei Shtylyov Nov. 12, 2015, 3:04 p.m. UTC | #1

Hello.

On 11/12/2015 5:31 PM, Wolfram Sang wrote:

> From: Wolfram Sang <[e-mail]>
>
> After making sure to reinit the HW and clear interrupts in the timeout
> case, we know that interrupts are always disabled in the sections
> protected by the spinlock.

    What about SMP? Spinlocks are mostly necessary for the SMP support, their 
tole isn't limited to disabling interrupts...

> Thus, we can simply remove it which is a
> preparation for further refactoring. While here, rename the timeout
> variable to time_left which is way more readable.
>
> Signed-off-by: Wolfram Sang <[e-mail]>

[...]

MBR, Sergei

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Wolfram Sang Nov. 12, 2015, 3:52 p.m. UTC | #2

On Thu, Nov 12, 2015 at 06:04:27PM +0300, Sergei Shtylyov wrote:
> Hello.
> 
> On 11/12/2015 5:31 PM, Wolfram Sang wrote:
> 
> >From: Wolfram Sang <[e-mail]>
> >
> >After making sure to reinit the HW and clear interrupts in the timeout
> >case, we know that interrupts are always disabled in the sections
> >protected by the spinlock.
> 
>    What about SMP? Spinlocks are mostly necessary for the SMP support, their
> tole isn't limited to disabling interrupts...

We have per-adapter locks in the core. Once a transfer is started, you
can't access the adapter unless the transfer is finished. But then, all
interrupts are off again.

Patch

diff --git a/drivers/i2c/busses/i2c-rcar.c b/drivers/i2c/busses/i2c-rcar.c
index 746406923a5825..0f2dc74ab8bcc1 100644
--- a/drivers/i2c/busses/i2c-rcar.c
+++ b/drivers/i2c/busses/i2c-rcar.c
@@ -33,7 +33,6 @@ 
 #include <linux/platform_device.h>
 #include <linux/pm_runtime.h>
 #include <linux/slab.h>
-#include <linux/spinlock.h>
 
 /* register offsets */
 #define ICSCR	0x00	/* slave ctrl */
@@ -110,7 +109,6 @@  struct rcar_i2c_priv {
 	struct i2c_msg	*msg;
 	struct clk *clk;
 
-	spinlock_t lock;
 	wait_queue_head_t wait;
 
 	int pos;
@@ -429,9 +427,6 @@  static irqreturn_t rcar_i2c_irq(int irq, void *ptr)
 	irqreturn_t result = IRQ_HANDLED;
 	u32 msr;
 
-	/*-------------- spin lock -----------------*/
-	spin_lock(&priv->lock);
-
 	if (rcar_i2c_slave_irq(priv))
 		goto exit;
 
@@ -478,9 +473,6 @@  out:
 	}
 
 exit:
-	spin_unlock(&priv->lock);
-	/*-------------- spin unlock -----------------*/
-
 	return result;
 }
 
@@ -490,9 +482,8 @@  static int rcar_i2c_master_xfer(struct i2c_adapter *adap,
 {
 	struct rcar_i2c_priv *priv = i2c_get_adapdata(adap);
 	struct device *dev = rcar_i2c_priv_to_dev(priv);
-	unsigned long flags;
 	int i, ret;
-	long timeout;
+	long time_left;
 
 	pm_runtime_get_sync(dev);
 
@@ -507,9 +498,6 @@  static int rcar_i2c_master_xfer(struct i2c_adapter *adap,
 			break;
 		}
 
-		/*-------------- spin lock -----------------*/
-		spin_lock_irqsave(&priv->lock, flags);
-
 		/* init each data */
 		priv->msg	= &msgs[i];
 		priv->pos	= 0;
@@ -519,13 +507,11 @@  static int rcar_i2c_master_xfer(struct i2c_adapter *adap,
 
 		rcar_i2c_prepare_msg(priv);
 
-		spin_unlock_irqrestore(&priv->lock, flags);
-		/*-------------- spin unlock -----------------*/
-
-		timeout = wait_event_timeout(priv->wait,
+		time_left = wait_event_timeout(priv->wait,
 					     rcar_i2c_flags_has(priv, ID_DONE),
 					     adap->timeout);
-		if (!timeout) {
+		if (!time_left) {
+			rcar_i2c_init(priv);
 			ret = -ETIMEDOUT;
 			break;
 		}
@@ -656,7 +642,6 @@  static int rcar_i2c_probe(struct platform_device *pdev)
 
 	irq = platform_get_irq(pdev, 0);
 	init_waitqueue_head(&priv->wait);
-	spin_lock_init(&priv->lock);
 
 	adap = &priv->adap;
 	adap->nr = pdev->id;