linux-kernel - Re: [PATCH v3] i2c: mux: remove duplicated i2c

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Message-ID: <99cfa6a2-9a60-6bdd-2542-9dd78af75758@axentia.se>
Date:   Mon, 8 Oct 2018 21:43:55 +0000
From:   Peter Rosin <peda@...ntia.se>
To:     Luca Ceresoli <lucaceresoli77@...il.com>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Luca Ceresoli <luca@...aceresoli.net>,
        Wolfram Sang <wsa@...-dreams.de>
Subject: Re: [PATCH v3] i2c: mux: remove duplicated i2c_algorithm

On 2018-10-03 17:19, 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.

Ouch, while I like the concept of having one i2c_algorithm per mux,
this patch is not working. Various i2c-mux drivers set the
muxc->mux_locked variable *after* the i2c_mux_alloc call, and this
patch breaks such use.

So, the patch needs some reworking. Sorry for not noticing this
earlier.

Cheers,
Peter

> Cc: Peter Rosin <peda@...ntia.se>
> Signed-off-by: Luca Ceresoli <luca@...aceresoli.net>
> 
> ---
> 
> Changes v2 -> v3:
>  - fix coding style of comment when moving it (Peter Rosin)
>  - move the 'algo' member between parent and dev (Peter Rosin)
> 
> Changes v1 -> v2:
>  - include i2c.h (fixes build failure on i2c-mux-ltc4306)
> ---
>  drivers/i2c/i2c-mux.c   | 38 +++++++++++++++++++-------------------
>  include/linux/i2c-mux.h |  2 ++
>  2 files changed, 21 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/i2c/i2c-mux.c b/drivers/i2c/i2c-mux.c
> index f330690b4125..6ac23004fb2a 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 +262,24 @@ 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.
> +	 */
> +	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 +318,11 @@ 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..3d89600d5a9e 100644
> --- a/include/linux/i2c-mux.h
> +++ b/include/linux/i2c-mux.h
> @@ -28,9 +28,11 @@
>  #ifdef __KERNEL__
>  
>  #include <linux/bitops.h>
> +#include <linux/i2c.h>
>  
>  struct i2c_mux_core {
>  	struct i2c_adapter *parent;
> +	struct i2c_algorithm algo;
>  	struct device *dev;
>  	unsigned int mux_locked:1;
>  	unsigned int arbitrator:1;
>