linux-kernel - Re: [PATCH v2 5/8] i2c: mux: add support for 'i2c-mux', 'i2c-arb' and 'i2c-gate' DT subnodes

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Date:	Mon, 15 Aug 2016 16:33:51 +0200
From:	Peter Rosin <peda@...ntia.se>
To:	Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>,
	<linux-kernel@...r.kernel.org>
CC:	Wolfram Sang <wsa@...-dreams.de>, Rob Herring <robh+dt@...nel.org>,
	"Mark Rutland" <mark.rutland@....com>,
	Guenter Roeck <linux@...ck-us.net>,
	"David S. Miller" <davem@...emloft.net>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	<linux-i2c@...r.kernel.org>, <devicetree@...r.kernel.org>,
	"Crestez Dan Leonard" <leonard.crestez@...el.com>
Subject: Re: [PATCH v2 5/8] i2c: mux: add support for 'i2c-mux', 'i2c-arb' and
 'i2c-gate' DT subnodes

Hi Vladimir,

On 2016-08-15 15:55, Vladimir Zapolskiy wrote:
> Hi Peter,
> 
> On 08/15/2016 04:40 PM, Peter Rosin wrote:
>> Backwards compatibility is preserved; the subnodes are in practice
>> optional.
>>
>> However, the mux core needs to know what subnode it should examine, so add
>> a couple of new flags for i2c_mux_alloc for this purpose.
>>
>> The rule is that if the mux core finds a 'reg' property in the appropriate
>> subnode, e.g. if 'reg' exists in the 'i2c-mux' subnode, then the mux core
>> will assume that this is an old style entry and not an i2c-mux subnode
>> (correspondingly for arbitrators and gates with 'i2c-arb' and 'i2c-gate').
>>
>> Signed-off-by: Peter Rosin <peda@...ntia.se>
>> ---
>>  drivers/i2c/i2c-mux.c   | 44 ++++++++++++++++++++++++++++++++++++--------
>>  include/linux/i2c-mux.h |  8 ++++++--
>>  2 files changed, 42 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/i2c/i2c-mux.c b/drivers/i2c/i2c-mux.c
>> index 8eee98634cda..c1ae719d1a7a 100644
>> --- a/drivers/i2c/i2c-mux.c
>> +++ b/drivers/i2c/i2c-mux.c
>> @@ -255,6 +255,10 @@ struct i2c_mux_core *i2c_mux_alloc(struct i2c_adapter *parent,
>>  	muxc->dev = dev;
>>  	if (flags & I2C_MUX_LOCKED)
>>  		muxc->mux_locked = true;
>> +	if (flags & I2C_MUX_ARBITRATOR)
>> +		muxc->arbitrator = true;
>> +	if (flags & I2C_MUX_GATE)
>> +		muxc->gate = true;
>>  	muxc->select = select;
>>  	muxc->deselect = deselect;
>>  	muxc->max_adapters = max_adapters;
>> @@ -335,18 +339,42 @@ int i2c_mux_add_adapter(struct i2c_mux_core *muxc,
>>  	 * nothing if !CONFIG_OF.
>>  	 */
>>  	if (muxc->dev->of_node) {
>> -		struct device_node *child;
>> +		struct device_node *dev_node = muxc->dev->of_node;
>> +		struct device_node *mux_node, *child = NULL;
>>  		u32 reg;
>>
>> -		for_each_child_of_node(muxc->dev->of_node, child) {
>> -			ret = of_property_read_u32(child, "reg", &reg);
>> -			if (ret)
>> -				continue;
>> -			if (chan_id == reg) {
>> -				priv->adap.dev.of_node = child;
>> -				break;
> 
> missing of_node_put(child);

Note, you are commenting on the old code that is removed, but I don't think
there was any bug. A reference is stored away for later use, so better not
of_node_put(child) or it might disappear from under us. Or do I have a
fundamental misunderstanding?

> Also adding an empty line would be perfect.

Strange comment for the split between removing and adding lines. What do you
mean? I certainly don't miss any empty lines here...

>> +		if (muxc->arbitrator)
>> +			mux_node = of_get_child_by_name(dev_node, "i2c-arb");
>> +		else if (muxc->gate)
>> +			mux_node = of_get_child_by_name(dev_node, "i2c-gate");
>> +		else
>> +			mux_node = of_get_child_by_name(dev_node, "i2c-mux");
>> +
>> +		if (mux_node) {
>> +			/* A "reg" property indicates an old-style DT entry */
>> +			if (!of_property_read_u32(mux_node, "reg", &reg)) {
>> +				of_node_put(mux_node);
>> +				mux_node = NULL;
>> +			}
>> +		}
>> +
>> +		if (!mux_node)
>> +			mux_node = of_node_get(dev_node);
>> +		else if (muxc->arbitrator || muxc->gate)
>> +			child = of_node_get(mux_node);
>> +
>> +		if (!child) {
>> +			for_each_child_of_node(mux_node, child) {
>> +				ret = of_property_read_u32(child, "reg", &reg);
>> +				if (ret)
>> +					continue;
>> +				if (chan_id == reg)
>> +					break;
> 
> missing of_node_put(child);

Here you are commenting on the new code, but I think the same argument
holds here as well. The reference to the child node is stored away...

>>  			}
>>  		}
>> +
>> +		priv->adap.dev.of_node = child;

...here, for later use (by i2c_add_adapter).

Anyway, IF the of node really should be put, this is orthogonal to what
I'm doing here, and the problem exists in other places as well (just grep
for "dev.of_node = of_node_get". So, that would be fodder for future
patches.

Cheers,
Peter

>> +		of_node_put(mux_node);
>>  	}
>>
>>  	/*
>> diff --git a/include/linux/i2c-mux.h b/include/linux/i2c-mux.h
>> index d4c1d12f900d..bd74d5706f3b 100644
>> --- a/include/linux/i2c-mux.h
>> +++ b/include/linux/i2c-mux.h
>> @@ -32,7 +32,9 @@
>>  struct i2c_mux_core {
>>  	struct i2c_adapter *parent;
>>  	struct device *dev;
>> -	bool mux_locked;
>> +	unsigned int mux_locked:1;
>> +	unsigned int arbitrator:1;
>> +	unsigned int gate:1;
>>
>>  	void *priv;
>>
>> @@ -51,7 +53,9 @@ struct i2c_mux_core *i2c_mux_alloc(struct i2c_adapter *parent,
>>  				   int (*deselect)(struct i2c_mux_core *, u32));
>>
>>  /* flags for i2c_mux_alloc */
>> -#define I2C_MUX_LOCKED BIT(0)
>> +#define I2C_MUX_LOCKED     BIT(0)
>> +#define I2C_MUX_ARBITRATOR BIT(1)
>> +#define I2C_MUX_GATE       BIT(2)
>>
>>  static inline void *i2c_mux_priv(struct i2c_mux_core *muxc)
>>  {
>>