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i2c: s3c2410: grab adapter lock while changing i2c clock 

We probably don't want to change I2C frequency while a transfer is in
progress.  The current implementation grabs a spinlock, but that only
protected the writes to IICCON when starting a message, it didn't protect
against clock changes in the middle of a transaction.

Note: The i2c-core already grabs the adapter lock before calling
s3c24xx_i2c_doxfer(), which ensures that only one caller is issuing a
xfer at a time. This means it is not necessary to disable interrupts
(spin_lock_irqsave) when changing frequencies, since there won't be
any i2c interrupts if there is no on-going xfer.

Lastly, i2c_lock_adapter() may cause the cpufreq_transition to sleep if
if a xfer is in progress, but this is ok since cpufreq notifiers are
called in a kernel thread, and there are already cases where it could
sleep, such as when using i2c to update the output of a voltage
regulator.

Note: the cpufreq part of this change has no functional affect on
	exynos, where the i2c clock is independent of the cpufreq.
	But, there is a slight perfomance boost since we no longer need to
	lock/unlock an additional spinlock.

Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
Signed-off-by: Naveen Krishna Chatradhi <ch.naveen@samsung.com>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
This commit is contained in:
Daniel Kurtz 2012-11-15 17:43:30 +05:30 committed by Wolfram Sang
parent 2693ac6988
commit 9bcd04bfbb
1 changed files with 2 additions and 8 deletions
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10
drivers/i2c/busses/i2c-s3c2410.c
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@ -60,7 +60,6 @@ enum s3c24xx_i2c_state {
};
struct s3c24xx_i2c {
spinlock_t lock;
wait_queue_head_t wait;
unsigned int quirks;
unsigned int suspended:1;
@ -541,8 +540,6 @@ static int s3c24xx_i2c_doxfer(struct s3c24xx_i2c *i2c,
goto out;
}
spin_lock_irq(&i2c->lock);
i2c->msg = msgs;
i2c->msg_num = num;
i2c->msg_ptr = 0;
@ -551,7 +548,6 @@ static int s3c24xx_i2c_doxfer(struct s3c24xx_i2c *i2c,
s3c24xx_i2c_enable_irq(i2c);
s3c24xx_i2c_message_start(i2c, msgs);
spin_unlock_irq(&i2c->lock);
timeout = wait_event_timeout(i2c->wait, i2c->msg_num == 0, HZ * 5);
@ -741,7 +737,6 @@ static int s3c24xx_i2c_cpufreq_transition(struct notifier_block *nb,
unsigned long val, void *data)
{
struct s3c24xx_i2c *i2c = freq_to_i2c(nb);
unsigned long flags;
unsigned int got;
int delta_f;
int ret;
@ -755,9 +750,9 @@ static int s3c24xx_i2c_cpufreq_transition(struct notifier_block *nb,
if ((val == CPUFREQ_POSTCHANGE && delta_f < 0) ||
(val == CPUFREQ_PRECHANGE && delta_f > 0)) {
spin_lock_irqsave(&i2c->lock, flags);
i2c_lock_adapter(&i2c->adap);
ret = s3c24xx_i2c_clockrate(i2c, &got);
spin_unlock_irqrestore(&i2c->lock, flags);
i2c_unlock_adapter(&i2c->adap);
if (ret < 0)
dev_err(i2c->dev, "cannot find frequency\n");
@ -962,7 +957,6 @@ static int s3c24xx_i2c_probe(struct platform_device *pdev)
i2c->adap.class = I2C_CLASS_HWMON | I2C_CLASS_SPD;
i2c->tx_setup = 50;
spin_lock_init(&i2c->lock);
init_waitqueue_head(&i2c->wait);
/* find the clock and enable it */