Re: [PATCH v3 1/2] i2c: mux: create symlink to actual mux device

[Guenter Roeck <linux-0h96xk9xTtrk1uMJSBkQmQ@public.gmane.org>]

On 11/13/2014 05:39 AM, Wolfram Sang wrote:
> The current implementation creates muxed i2c-<n> busses as immediate
> children of their i2c-<n> parent bus. In case of multiple muxes on one
> bus, it is impossible to determine which muxed bus comes from which mux.
>
> It could be argued that the parent device should be changed from the
> parent adapter to the mux device. This has pros and cons. To improve the
> topology, simply add a "muxed_device" symlink pointing to the actual
> muxing device, so we can distinguish muxed busses. Doing it this way, we
> don't break the ABI.
>
> Signed-off-by: Wolfram Sang <wsa-z923LK4zBo2bacvFa/9K2g@public.gmane.org>
> Cc: Jean Delvare <jdelvare-l3A5Bk7waGM@public.gmane.org>
> Cc: Guenter Roeck <linux-0h96xk9xTtrk1uMJSBkQmQ@public.gmane.org>
> Cc: Martin Belanger <martin.belanger-Ir6+u9MVKBtBDgjK7y7TUQ@public.gmane.org>
> Cc: Rodolfo Giometti <giometti-AVVDYK/kqiJWk0Htik3J/w@public.gmane.org>
> Cc: Michael Lawnick <ml.lawnick-Mmb7MZpHnFY@public.gmane.org>
> Cc: Jeroen De Wachter <jeroen.de.wachter-CNXmb7IdZIWZIoH1IeqzKA@public.gmane.org>
> Cc: Gerlando Falauto <gerlando.falauto-SkAbAL50j+5BDgjK7y7TUQ@public.gmane.org>

This version works for me and passes testing with our application code.

Tested-by: Guenter Roeck <linux-0h96xk9xTtrk1uMJSBkQmQ@public.gmane.org>

> ---
>   drivers/i2c/i2c-mux.c | 4 ++++
>   1 file changed, 4 insertions(+)
>
> diff --git a/drivers/i2c/i2c-mux.c b/drivers/i2c/i2c-mux.c
> index 2d0847b6be62..f246a9f7dd22 100644
> --- a/drivers/i2c/i2c-mux.c
> +++ b/drivers/i2c/i2c-mux.c
> @@ -183,6 +183,9 @@ struct i2c_adapter *i2c_add_mux_adapter(struct i2c_adapter *parent,
>   		return NULL;
>   	}
>
> +	WARN(sysfs_create_link(&priv->adap.dev.kobj, &mux_dev->kobj, "mux_device"),
> +			       "can't create symlink to mux device\n");
> +
>   	dev_info(&parent->dev, "Added multiplexed i2c bus %d\n",
>   		 i2c_adapter_id(&priv->adap));
>
> @@ -194,6 +197,7 @@ void i2c_del_mux_adapter(struct i2c_adapter *adap)
>   {
>   	struct i2c_mux_priv *priv = adap->algo_data;
>
> +	sysfs_remove_link(&priv->adap.dev.kobj, "mux_device");
>   	i2c_del_adapter(adap);
>   	kfree(priv);
>   }
>