[RFC] i2c: Providing hooks for i2c multimaster bus arbitration.

[Yuvaraj Kumar]

Below are the links on multi master bus arbitration where it has been
discussing.

 http://comments.gmane.org/gmane.linux.kernel/1410276

 http://www.kernelhub.org/?msg=179505&p=2


On Mon, Feb 4, 2013 at 2:33 PM, Yuvaraj Kumar C D <yuvaraj.cd at gmail.com> wrote:
> This RFC patch is w.r.t multimaster bus arbitration which is already
> being discussing in the mainline.
> This patch provides hooks for the i2c multimaster bus arbitration
> and to have the arbitration parameters.
>
> Signed-off-by: Yuvaraj Kumar C D <yuvaraj.cd at samsung.com>
> ---
>  drivers/i2c/i2c-core.c |   13 ++++++++++++-
>  include/linux/i2c.h    |   12 ++++++++++++
>  2 files changed, 24 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
> index e388590..ed89fc8 100644
> --- a/drivers/i2c/i2c-core.c
> +++ b/drivers/i2c/i2c-core.c
> @@ -1408,18 +1408,29 @@ int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
>                                 (msgs[ret].flags & I2C_M_RECV_LEN) ? "+" : "");
>                 }
>  #endif
> +               if (adap->mm_arbit_algo) {
> +                       ret = adap->mm_arbit_algo->i2c_mm_bus_get(adap);
> +                       if (ret)
> +                               /* I2C bus under control of another master. */
> +                               return -EAGAIN;
> +               }
>
>                 if (in_atomic() || irqs_disabled()) {
>                         ret = i2c_trylock_adapter(adap);
> -                       if (!ret)
> +                       if (!ret && adap->mm_arbit_algo) {
> +                               adap->mm_arbit_algo->i2c_mm_bus_release(adap);
> +
>                                 /* I2C activity is ongoing. */
>                                 return -EAGAIN;
> +                       }
>                 } else {
>                         i2c_lock_adapter(adap);
>                 }
>
>                 ret = __i2c_transfer(adap, msgs, num);
>                 i2c_unlock_adapter(adap);
> +               if (adap->mm_arbit_algo)
> +                       adap->mm_arbit_algo->i2c_mm_bus_release(adap);
>
>                 return ret;
>         } else {
> diff --git a/include/linux/i2c.h b/include/linux/i2c.h
> index d0c4db7..61fbfe3 100644
> --- a/include/linux/i2c.h
> +++ b/include/linux/i2c.h
> @@ -371,6 +371,17 @@ struct i2c_algorithm {
>  };
>
>  /*
> + *This struct provides hooks for i2c multi-master arbitration needs.
> + */
> +struct i2c_mm_arbitration {
> +       void *arbitration_data;
> +
> +       /* Should return 0 if mastership could be successfully established */
> +       int (*i2c_mm_bus_get)(struct i2c_adapter *adap);
> +       void (*i2c_mm_bus_release)(struct i2c_adapter *adap);
> +};
> +
> +/*
>   * i2c_adapter is the structure used to identify a physical i2c bus along
>   * with the access algorithms necessary to access it.
>   */
> @@ -393,6 +404,7 @@ struct i2c_adapter {
>
>         struct mutex userspace_clients_lock;
>         struct list_head userspace_clients;
> +       struct i2c_mm_arbitration *mm_arbit_algo;
>  };
>  #define to_i2c_adapter(d) container_of(d, struct i2c_adapter, dev)
>
> --
> 1.7.9.5
>