linux-kernel - Re: [PATCH v6 01/24] i2c-mux: add common data for every i2c-mux instance

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Date:	Mon, 11 Apr 2016 22:46:30 +0200
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Peter Rosin <peda@...ator.liu.se>
Cc:	linux-kernel@...r.kernel.org, Peter Rosin <peda@...ntia.se>,
	Jonathan Corbet <corbet@....net>,
	Peter Korsgaard <peter.korsgaard@...co.com>,
	Guenter Roeck <linux@...ck-us.net>,
	Jonathan Cameron <jic23@...nel.org>,
	Hartmut Knaack <knaack.h@....de>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Peter Meerwald <pmeerw@...erw.net>,
	Antti Palosaari <crope@....fi>,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	Rob Herring <robh+dt@...nel.org>,
	Frank Rowand <frowand.list@...il.com>,
	Grant Likely <grant.likely@...aro.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"David S. Miller" <davem@...emloft.net>,
	Kalle Valo <kvalo@...eaurora.org>,
	Joe Perches <joe@...ches.com>, Jiri Slaby <jslaby@...e.com>,
	Daniel Baluta <daniel.baluta@...el.com>,
	Adriana Reus <adriana.reus@...el.com>,
	Lucas De Marchi <lucas.demarchi@...el.com>,
	Matt Ranostay <matt.ranostay@...el.com>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Terry Heo <terryheo@...gle.com>,
	Hans Verkuil <hans.verkuil@...co.com>,
	Arnd Bergmann <arnd@...db.de>,
	Tommi Rantala <tt.rantala@...il.com>,
	linux-i2c@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-iio@...r.kernel.org, linux-media@...r.kernel.org,
	devicetree@...r.kernel.org
Subject: Re: [PATCH v6 01/24] i2c-mux: add common data for every i2c-mux
 instance

Hi Peter,

first high-level review:

> +int i2c_mux_reserve_adapters(struct i2c_mux_core *muxc, int adapters)

I'd suggest to rename 'adapters' into 'num_adapters' throughout this
patch. I think it makes the code a lot easier to understand.

> +{
> +	struct i2c_adapter **adapter;
> +
> +	if (adapters <= muxc->max_adapters)
> +		return 0;
> +
> +	adapter = devm_kmalloc_array(muxc->dev,
> +				     adapters, sizeof(*adapter),
> +				     GFP_KERNEL);
> +	if (!adapter)
> +		return -ENOMEM;
> +
> +	if (muxc->adapter) {
> +		memcpy(adapter, muxc->adapter,
> +		       muxc->max_adapters * sizeof(*adapter));
> +		devm_kfree(muxc->dev, muxc->adapter);
> +	}
> +
> +	muxc->adapter = adapter;
> +	muxc->max_adapters = adapters;
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(i2c_mux_reserve_adapters);

Despite that I wonder why not using some of the realloc functions, I
wonder even more if we couldn't supply num_adapters to i2c_mux_alloc()
and reserve the memory statically. i2c busses are not
dynamic/hot-pluggable so that should be good enough?

> -	WARN(sysfs_create_link(&priv->adap.dev.kobj, &mux_dev->kobj, "mux_device"),
> -			       "can't create symlink to mux device\n");
> +	WARN(sysfs_create_link(&priv->adap.dev.kobj, &muxc->dev->kobj,
> +			       "mux_device"),

Ignoring the 80 char limit here makes the code more readable.

> +	     "can't create symlink to mux device\n");
>  
>  	snprintf(symlink_name, sizeof(symlink_name), "channel-%u", chan_id);
> -	WARN(sysfs_create_link(&mux_dev->kobj, &priv->adap.dev.kobj, symlink_name),
> -			       "can't create symlink for channel %u\n", chan_id);
> +	WARN(sysfs_create_link(&muxc->dev->kobj, &priv->adap.dev.kobj,
> +			       symlink_name),

ditto.

> +	     "can't create symlink for channel %u\n", chan_id);
>  	dev_info(&parent->dev, "Added multiplexed i2c bus %d\n",
>  		 i2c_adapter_id(&priv->adap));
>  
> -	return &priv->adap;
> +	muxc->adapter[muxc->adapters++] = &priv->adap;
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(i2c_mux_add_adapter);
> +
> +struct i2c_mux_core *i2c_mux_one_adapter(struct i2c_adapter *parent,
> +					 struct device *dev, int sizeof_priv,
> +					 u32 flags, u32 force_nr,
> +					 u32 chan_id, unsigned int class,
> +					 int (*select)(struct i2c_mux_core *,
> +						       u32),

ditto

> +					 int (*deselect)(struct i2c_mux_core *,
> +							 u32))

ditto

> +{
> +	struct i2c_mux_core *muxc;
> +	int ret;
> +
> +	muxc = i2c_mux_alloc(parent, dev, sizeof_priv, flags, select, deselect);
> +	if (!muxc)
> +		return ERR_PTR(-ENOMEM);
> +
> +	ret = i2c_mux_add_adapter(muxc, force_nr, chan_id, class);
> +	if (ret) {
> +		devm_kfree(dev, muxc);
> +		return ERR_PTR(ret);
> +	}
> +
> +	return muxc;
> +}
> +EXPORT_SYMBOL_GPL(i2c_mux_one_adapter);

Are you sure the above function pays off? Its argument list is very
complex and it doesn't save a lot of code. Having seperate calls is
probably more understandable in drivers? Then again, I assume it makes
the conversion of existing drivers easier.

So much for now. Thanks!

   Wolfram


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