linux-kernel - Re: [PATCH v2] i2c: mux: remove duplicated i2c

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Message-ID: <9fcca887-1ade-e3bf-67f7-aecd8a60dafb@axentia.se>
Date:   Mon, 1 Oct 2018 13:55:26 +0200
From:   Peter Rosin <peda@...ntia.se>
To:     Luca Ceresoli <lucaceresoli77@...il.com>, linux-i2c@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Luca Ceresoli <luca@...aceresoli.net>,
        Wolfram Sang <wsa@...-dreams.de>
Subject: Re: [PATCH v2] i2c: mux: remove duplicated i2c_algorithm

On 2018-09-27 15:38, Luca Ceresoli wrote:
> From: Luca Ceresoli <luca@...aceresoli.net>
> 
> i2c-mux instantiates one i2c_algorithm for each downstream adapter.
> However these algorithms are all identical, depending only on the
> parent adapter.
> 
> Avoid duplication by hoisting the i2c_algorithm from the adapters to
> the i2c_mux_core object, and reuse it in all the adapters.

Looks about right to me, just a couple of nit-picks. See below.

> 
> Signed-off-by: Luca Ceresoli <luca@...aceresoli.net>
> 
> ---
> 
> Changes v1 -> v2:
>  - include i2c.h (fixes build failure on i2c-mux-ltc4306)
> ---
>  drivers/i2c/i2c-mux.c   | 37 ++++++++++++++++++-------------------
>  include/linux/i2c-mux.h |  2 ++
>  2 files changed, 20 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/i2c/i2c-mux.c b/drivers/i2c/i2c-mux.c
> index f330690b4125..2b0cc2ad0a17 100644
> --- a/drivers/i2c/i2c-mux.c
> +++ b/drivers/i2c/i2c-mux.c
> @@ -30,7 +30,6 @@
>  /* multiplexer per channel data */
>  struct i2c_mux_priv {
>  	struct i2c_adapter adap;
> -	struct i2c_algorithm algo;
>  	struct i2c_mux_core *muxc;
>  	u32 chan_id;
>  };
> @@ -263,6 +262,23 @@ struct i2c_mux_core *i2c_mux_alloc(struct i2c_adapter *parent,
>  	muxc->deselect = deselect;
>  	muxc->max_adapters = max_adapters;
>  
> +	/* Need to do algo dynamically because we don't know ahead
> +	 * of time what sort of physical adapter we'll be dealing with.
> +	 */

Multiline comments should start with a /* on a line of its own. Yes,
I know you just moved it, but please fix it up as you do so.

> +	if (parent->algo->master_xfer) {
> +		if (muxc->mux_locked)
> +			muxc->algo.master_xfer = i2c_mux_master_xfer;
> +		else
> +			muxc->algo.master_xfer = __i2c_mux_master_xfer;
> +	}
> +	if (parent->algo->smbus_xfer) {
> +		if (muxc->mux_locked)
> +			muxc->algo.smbus_xfer = i2c_mux_smbus_xfer;
> +		else
> +			muxc->algo.smbus_xfer = __i2c_mux_smbus_xfer;
> +	}
> +	muxc->algo.functionality = i2c_mux_functionality;
> +
>  	return muxc;
>  }
>  EXPORT_SYMBOL_GPL(i2c_mux_alloc);
> @@ -301,28 +317,11 @@ int i2c_mux_add_adapter(struct i2c_mux_core *muxc,
>  	priv->muxc = muxc;
>  	priv->chan_id = chan_id;
>  
> -	/* Need to do algo dynamically because we don't know ahead
> -	 * of time what sort of physical adapter we'll be dealing with.
> -	 */
> -	if (parent->algo->master_xfer) {
> -		if (muxc->mux_locked)
> -			priv->algo.master_xfer = i2c_mux_master_xfer;
> -		else
> -			priv->algo.master_xfer = __i2c_mux_master_xfer;
> -	}
> -	if (parent->algo->smbus_xfer) {
> -		if (muxc->mux_locked)
> -			priv->algo.smbus_xfer = i2c_mux_smbus_xfer;
> -		else
> -			priv->algo.smbus_xfer = __i2c_mux_smbus_xfer;
> -	}
> -	priv->algo.functionality = i2c_mux_functionality;
> -
>  	/* Now fill out new adapter structure */
>  	snprintf(priv->adap.name, sizeof(priv->adap.name),
>  		 "i2c-%d-mux (chan_id %d)", i2c_adapter_id(parent), chan_id);
>  	priv->adap.owner = THIS_MODULE;
> -	priv->adap.algo = &priv->algo;
> +	priv->adap.algo = &muxc->algo;
>  	priv->adap.algo_data = priv;
>  	priv->adap.dev.parent = &parent->dev;
>  	priv->adap.retries = parent->retries;
> diff --git a/include/linux/i2c-mux.h b/include/linux/i2c-mux.h
> index bd74d5706f3b..5a4ffca99f5d 100644
> --- a/include/linux/i2c-mux.h
> +++ b/include/linux/i2c-mux.h
> @@ -28,6 +28,7 @@
>  #ifdef __KERNEL__
>  
>  #include <linux/bitops.h>
> +#include <linux/i2c.h>
>  
>  struct i2c_mux_core {
>  	struct i2c_adapter *parent;
> @@ -36,6 +37,7 @@ struct i2c_mux_core {
>  	unsigned int arbitrator:1;
>  	unsigned int gate:1;
>  
> +	struct i2c_algorithm algo;
>  	void *priv;

I want the algo member further up, and certainly not "grouped" with
priv. Between parent and dev seems fine to me.

Cheers,
Peter

>  
>  	int (*select)(struct i2c_mux_core *, u32 chan_id);
>