linux-kernel - Re: [PATCH] i2c: i2c-core: do not use bus internal data

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Message-ID: <20160314091819.GA27975@ulmo>
Date:	Mon, 14 Mar 2016 10:18:19 +0100
From:	Thierry Reding <thierry.reding@...il.com>
To:	Sudip Mukherjee <sudipm.mukherjee@...il.com>
Cc:	Wolfram Sang <wsa@...-dreams.de>, linux-kernel@...r.kernel.org,
	linux-i2c@...r.kernel.org, gregkh@...uxfoundation.org
Subject: Re: [PATCH] i2c: i2c-core: do not use bus internal data

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@...ethink.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.

Thierry

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