Re: [PATCH 3/3] iio: ak8975: Don't bail out for irq setup error

[Jonathan Cameron <jic23@kernel.org>]

On 11/03/14 21:15, Srinivas Pandruvada wrote:
> This driver can very well work via polling, if request_irq failed.
> The problem is that many times i2c interrupts are shared. This
> driver is not ready for shared interrupt as it will return IRQ_HANDLED,
> in every case. Here we will get EBUSY when some other driver registered
> handler and this driver is grabbing in exclusive mode.
> So in this case just print error and continue in polling mode.
>
> Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
I'm not sure this is a good solution as it means that we will get very different
results depending on the probe order of various drivers.  How do other i2c drivers
cope with the fact that there is no way of knowing within the interrupt routine
that the device was the one causing the interrupt?

A quick grep suggests that the normal trick is to had over to an irq thread
then return IRQ_NONE from that once we know it isn't our irq.  Could we have
move the queue wakeup into a a thread (converting to a threaded interrupt) but
before it query the hardware to establish it is actually our interrupt?
> ---
>   drivers/iio/magnetometer/ak8975.c | 12 +++++++++---
>   1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/iio/magnetometer/ak8975.c b/drivers/iio/magnetometer/ak8975.c
> index fe5e9c8..0f9c407 100644
> --- a/drivers/iio/magnetometer/ak8975.c
> +++ b/drivers/iio/magnetometer/ak8975.c
> @@ -236,9 +236,15 @@ static int ak8975_setup(struct i2c_client *client)
>   	if (data->eoc_gpio > 0 || client->irq) {
>   		ret = ak8975_setup_irq(data);
>   		if (ret < 0) {
> -			dev_err(&client->dev,
> -				"Error setting data ready interrupt\n");
> -			return ret;
> +			if (ret == -EBUSY) {
> +				dev_err(&client->dev,
> +					"device Intr busy:polling required\n");
> +				ret = 0;
> +			} else {
> +				dev_err(&client->dev,
> +					"Error setting data ready interrupt\n");
> +				return ret;
> +			}
>   		}
>   	}
>
>