On Mon, Mar 14, 2016 at 10:18:19AM +0100, Thierry Reding wrote:
> On Mon, Mar 07, 2016 at 05:19:17PM +0530, Sudip Mukherjee wrote:
> > The variable p is a data structure which is used by the driver core
> > internally and it is not expected that busses will be directly accessing
> > these driver core internal only data.
> > 
> > Signed-off-by: Sudip Mukherjee <sudip.mukherjee@codethink.co.uk>
> > ---
> > 
> > Reference of Greg's comment about it at:
> > https://lkml.org/lkml/2016/3/5/171
> > 
> >  drivers/i2c/i2c-core.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
> > index 2949ab3..2f31fb5 100644
> > --- a/drivers/i2c/i2c-core.c
> > +++ b/drivers/i2c/i2c-core.c
> > @@ -73,6 +73,7 @@ static struct device_type i2c_client_type;
> >  static int i2c_detect(struct i2c_adapter *adapter, struct i2c_driver *driver);
> >  
> >  static struct static_key i2c_trace_msg = STATIC_KEY_INIT_FALSE;
> > +static bool is_registered;
> >  
> >  void i2c_transfer_trace_reg(void)
> >  {
> > @@ -1529,7 +1530,7 @@ static int i2c_register_adapter(struct i2c_adapter *adap)
> >  	int res = 0;
> >  
> >  	/* Can't register until after driver model init */
> > -	if (unlikely(WARN_ON(!i2c_bus_type.p))) {
> > +	if (unlikely(WARN_ON(!is_registered))) {
> >  		res = -EAGAIN;
> >  		goto out_list;
> >  	}
> > @@ -1926,7 +1927,7 @@ int i2c_register_driver(struct module *owner, struct i2c_driver *driver)
> >  	int res;
> >  
> >  	/* Can't register until after driver model init */
> > -	if (unlikely(WARN_ON(!i2c_bus_type.p)))
> > +	if (unlikely(WARN_ON(!is_registered)))
> >  		return -EAGAIN;
> >  
> >  	/* add the driver to the list of i2c drivers in the driver core */
> > @@ -2118,6 +2119,7 @@ static int __init i2c_init(void)
> >  	if (IS_ENABLED(CONFIG_OF_DYNAMIC))
> >  		WARN_ON(of_reconfig_notifier_register(&i2c_of_notifier));
> >  
> > +	is_registered = true;
> >  	return 0;
> >  
> >  class_err:
> 
> This doesn't work. I see a number of these WARN_ON()s trigger and I
> think the reason is that i2c_init() always fails now. The cause seems to
> be that i2c_init() calls i2c_add_driver(&dummy_driver), which will now
> always fail, because is_register is set to true *after* that call. There
> is no way I see I2C working at all after this patch.

FWIW, the below on top of your patch seems to fix things for me.

Thierry

--- >8 ---
diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index f4726cdbb06a..f8723a474e28 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -2112,6 +2112,8 @@ static int __init i2c_init(void)
 		goto bus_err;
 	}
 #endif
+	is_registered = true;
+
 	retval = i2c_add_driver(&dummy_driver);
 	if (retval)
 		goto class_err;
@@ -2119,7 +2121,6 @@ static int __init i2c_init(void)
 	if (IS_ENABLED(CONFIG_OF_DYNAMIC))
 		WARN_ON(of_reconfig_notifier_register(&i2c_of_notifier));
 
-	is_registered = true;
 	return 0;
 
 class_err: