On 03/15/2013 05:26 PM, Naveen Krishna Chatradhi wrote:
> This patch does the following
> 1. Handle the return values of wait_for_completion_interruptible_timeout
> 2. Add spin locks to avoid race conditions during ISR.
>
> Signed-off-by: Naveen Krishna Chatradhi <ch.nav...@samsung.com>
> Cc: Doug Anderson <diand...@chromium.org>
> Cc: Lars-Peter Clausen <l...@metafoo.de>
> ---
> Discussion thread for this patch can be found at
> http://www.gossamer-threads.com/lists/linux/kernel/1693284?page=last
>
> I've not seen any reference to spin lock usage in IIO.
> Kindly, suggest me if there is a better way to avoid the race.
>
> Thanks,
> Naveen
> drivers/iio/adc/exynos_adc.c | 14 ++++++++++++--
> 1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/iio/adc/exynos_adc.c b/drivers/iio/adc/exynos_adc.c
> index ed6fdd7..4de28ae 100644
> --- a/drivers/iio/adc/exynos_adc.c
> +++ b/drivers/iio/adc/exynos_adc.c
> @@ -91,6 +91,7 @@ struct exynos_adc {
>
> struct completion completion;
>
> + spinlock_t reg_lock;
> u32 value;
> unsigned int version;
> };
> @@ -117,7 +118,7 @@ static int exynos_read_raw(struct iio_dev *indio_dev,
> long mask)
> {
> struct exynos_adc *info = iio_priv(indio_dev);
> - unsigned long timeout;
> + long timeout;
> u32 con1, con2;
>
> if (mask != IIO_CHAN_INFO_RAW)
> @@ -143,15 +144,19 @@ static int exynos_read_raw(struct iio_dev *indio_dev,
> ADC_V1_CON(info->regs));
> }
>
> + INIT_COMPLETION(info->completion);
> +
This needs to happen before you start the transfer.
> timeout = wait_for_completion_interruptible_timeout
> (&info->completion, EXYNOS_ADC_TIMEOUT);
> +
> *val = info->value;
>
> mutex_unlock(&indio_dev->mlock);
>
> if (timeout == 0)
> return -ETIMEDOUT;
> -
> + else if (timeout < 0)
> + return timeout;
> return IIO_VAL_INT;
> }
>
> @@ -159,6 +164,8 @@ static irqreturn_t exynos_adc_isr(int irq, void *dev_id)
> {
> struct exynos_adc *info = (struct exynos_adc *)dev_id;
>
> + spin_lock(&info->reg_lock);
> +
> /* Read value */
> info->value = readl(ADC_V1_DATX(info->regs)) &
> ADC_DATX_MASK;
> @@ -170,6 +177,8 @@ static irqreturn_t exynos_adc_isr(int irq, void *dev_id)
>
> complete(&info->completion);
>
> + spin_unlock(&info->reg_lock);
> +
What exactly is the spinlock protecting against here? Concurrent runs of
exynos_adc_isr? This is probably not issue in the first place.
What you want to protect against is that completion is completed between the
call to INIT_COMPLETION() and the start of a new conversion. So the sections
that need to be under the spinlock are the complete call here and the point
from INIT_COMPLETION until the transfer is started in exynos_read_raw(). Make
sure to use spin_lock_irq there.
> return IRQ_HANDLED;
> }
>
> @@ -327,6 +336,7 @@ static int exynos_adc_probe(struct platform_device *pdev)
> else
> indio_dev->num_channels = MAX_ADC_V2_CHANNELS;
>
> + spin_lock_init(&info->reg_lock);
> ret = iio_device_register(indio_dev);
> if (ret)
> goto err_irq;
--
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