linux-kernel - Re: [PATCH 1/6] drivers/i2c: Update i2c_trace

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Date:   Tue, 3 Apr 2018 15:20:32 +0200
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Davidlohr Bueso <dave@...olabs.net>,
        David Howells <dhowells@...hat.com>
Cc:     peterz@...radead.org, mingo@...nel.org, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
        Davidlohr Bueso <dbueso@...e.de>
Subject: Re: [PATCH 1/6] drivers/i2c: Update i2c_trace_msg static key to
 modern api

On Mon, Mar 26, 2018 at 02:09:24PM -0700, Davidlohr Bueso wrote:
> No changes in refcount semantics -- key init is false; replace
> 
> static_key_slow_inc|dec   with   static_branch_inc|dec
> static_key_false          with   static_branch_unlikely
> 
> Added a '_key' suffix to i2c_trace_msg, for better self
> documentation.
> 

CCing David who wrote the original code

> Cc: Wolfram Sang <wsa@...-dreams.de>
> Cc: linux-i2c@...r.kernel.org
> Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
> ---
>  drivers/i2c/i2c-core-base.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
> index 16a3b73375a6..bfcff2a6f0a3 100644
> --- a/drivers/i2c/i2c-core-base.c
> +++ b/drivers/i2c/i2c-core-base.c
> @@ -69,18 +69,18 @@ static DEFINE_IDR(i2c_adapter_idr);
>  
>  static int i2c_detect(struct i2c_adapter *adapter, struct i2c_driver *driver);
>  
> -static struct static_key i2c_trace_msg = STATIC_KEY_INIT_FALSE;
> +static DEFINE_STATIC_KEY_FALSE(i2c_trace_msg_key);
>  static bool is_registered;
>  
>  int i2c_transfer_trace_reg(void)
>  {
> -	static_key_slow_inc(&i2c_trace_msg);
> +	static_branch_inc(&i2c_trace_msg_key);
>  	return 0;
>  }
>  
>  void i2c_transfer_trace_unreg(void)
>  {
> -	static_key_slow_dec(&i2c_trace_msg);
> +	static_branch_dec(&i2c_trace_msg_key);
>  }
>  
>  const struct i2c_device_id *i2c_match_id(const struct i2c_device_id *id,
> @@ -1848,11 +1848,12 @@ int __i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
>  	if (adap->quirks && i2c_check_for_quirks(adap, msgs, num))
>  		return -EOPNOTSUPP;
>  
> -	/* i2c_trace_msg gets enabled when tracepoint i2c_transfer gets
> +	/*
> +	 * i2c_trace_msg_key gets enabled when tracepoint i2c_transfer gets
>  	 * enabled.  This is an efficient way of keeping the for-loop from
>  	 * being executed when not needed.
>  	 */
> -	if (static_key_false(&i2c_trace_msg)) {
> +	if (static_branch_unlikely(&i2c_trace_msg_key)) {
>  		int i;
>  		for (i = 0; i < num; i++)
>  			if (msgs[i].flags & I2C_M_RD)
> @@ -1871,7 +1872,7 @@ int __i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
>  			break;
>  	}
>  
> -	if (static_key_false(&i2c_trace_msg)) {
> +	if (static_branch_unlikely(&i2c_trace_msg_key)) {
>  		int i;
>  		for (i = 0; i < ret; i++)
>  			if (msgs[i].flags & I2C_M_RD)
> -- 
> 2.13.6
> 

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