linux-kernel - Re: [PATCH 1/3] i2c: append hardware lock with bus lock

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Message-ID: <20110428102212.2d8d607c@endymion.delvare>
Date:	Thu, 28 Apr 2011 10:22:12 +0200
From:	Jean Delvare <khali@...ux-fr.org>
To:	Haojian Zhuang <haojian.zhuang@...il.com>
Cc:	eric.y.miao@...il.com, linux@....linux.org.uk,
	linux-arm-kernel@...ts.infradead.org, ben-linux@...ff.org,
	linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] i2c: append hardware lock with bus lock

Hi Haojian,

On Thu, 28 Apr 2011 12:02:36 +0800, Haojian Zhuang wrote:
> Both AP and CP are contained in Marvell PXA910 silicon. These two ARM
> cores are sharing one pair of I2C pins.
> 
> In order to keep I2C transaction operated with atomic, hardware lock
> (RIPC) is required. Because of this, bus lock in AP side can't afford
> this requirement. Now hardware lock is appended.

I have no objection to the idea, but one question: when using the
hardware lock, isn't the software mutex redundant? I would expect that
you call the hardware_lock/unlock functions _instead_ of
rt_mutex_lock/unlock, rather than in addition to it. Or do you still
need the rt_mutex to prevent priority inversion?

> 
> Signed-off-by: Haojian Zhuang <haojian.zhuang@...vell.com>
> Cc: Ben Dooks <ben-linux@...ff.org>
> ---
>  drivers/i2c/i2c-core.c |   22 ++++++++++++++++++----
>  include/linux/i2c.h    |    3 +++
>  2 files changed, 21 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
> index 045ba6e..412c7a5 100644
> --- a/drivers/i2c/i2c-core.c
> +++ b/drivers/i2c/i2c-core.c
> @@ -448,8 +448,11 @@ void i2c_lock_adapter(struct i2c_adapter *adapter)
>  
>  	if (parent)
>  		i2c_lock_adapter(parent);
> -	else
> +	else {
>  		rt_mutex_lock(&adapter->bus_lock);
> +		if (adapter->hardware_lock)
> +			adapter->hardware_lock();
> +	}
>  }
>  EXPORT_SYMBOL_GPL(i2c_lock_adapter);
>  
> @@ -460,11 +463,19 @@ EXPORT_SYMBOL_GPL(i2c_lock_adapter);
>  static int i2c_trylock_adapter(struct i2c_adapter *adapter)
>  {
>  	struct i2c_adapter *parent = i2c_parent_is_i2c_adapter(adapter);
> +	int ret = 0;
>  
>  	if (parent)
>  		return i2c_trylock_adapter(parent);
> -	else
> -		return rt_mutex_trylock(&adapter->bus_lock);
> +	else {
> +		ret = rt_mutex_trylock(&adapter->bus_lock);
> +		if (ret && adapter->hardware_trylock) {
> +			ret = adapter->hardware_trylock();
> +			if (!ret)
> +				i2c_unlock_adapter(adapter);
> +		}
> +		return ret;
> +	}
>  }
>  
>  /**
> @@ -477,8 +488,11 @@ void i2c_unlock_adapter(struct i2c_adapter *adapter)
>  
>  	if (parent)
>  		i2c_unlock_adapter(parent);
> -	else
> +	else {
> +		if (adapter->hardware_unlock)
> +			adapter->hardware_unlock();
>  		rt_mutex_unlock(&adapter->bus_lock);
> +	}
>  }
>  EXPORT_SYMBOL_GPL(i2c_unlock_adapter);
>  
> diff --git a/include/linux/i2c.h b/include/linux/i2c.h
> index 06a8d9c..b283b4e 100644
> --- a/include/linux/i2c.h
> +++ b/include/linux/i2c.h
> @@ -361,6 +361,9 @@ struct i2c_adapter {
>  
>  	/* data fields that are valid for all devices	*/
>  	struct rt_mutex bus_lock;
> +	void (*hardware_lock)(void);
> +	void (*hardware_unlock)(void);
> +	int (*hardware_trylock)(void);
>  
>  	int timeout;			/* in jiffies */
>  	int retries;


-- 
Jean Delvare
--
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