linux-kernel - Re: [PATCH 1/4] i2c: designware: No need to disable already disabled controller

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Date:	Mon, 2 Jun 2014 18:12:34 +0200
From:	Wolfram Sang <wsa@...-dreams.de>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	Yao Jin <yao.jin@...el.com>, Aubrey Li <aubrey.li@...el.com>,
	linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] i2c: designware: No need to disable already disabled
 controller

On Thu, May 15, 2014 at 05:37:21PM +0300, Mika Westerberg wrote:
> If the controller is already in desired state (enabled/disabled) there is
> no point in setting its state again.
> 
> Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> ---

Does it have a side-effect when setting then enable bit again? Otherwise
it will exit the loop immediately on the first try. Not too bad IMO
given the additional code saved.

>  drivers/i2c/busses/i2c-designware-core.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/i2c/busses/i2c-designware-core.c b/drivers/i2c/busses/i2c-designware-core.c
> index b58ecf19e767..b0792675b970 100644
> --- a/drivers/i2c/busses/i2c-designware-core.c
> +++ b/drivers/i2c/busses/i2c-designware-core.c
> @@ -258,6 +258,10 @@ static void __i2c_dw_enable(struct dw_i2c_dev *dev, bool enable)
>  {
>  	int timeout = 100;
>  
> +	/* In case the controller is already in desired state */
> +	if ((dw_readl(dev, DW_IC_ENABLE_STATUS) & 1) == enable)
> +		return;
> +
>  	do {
>  		dw_writel(dev, enable, DW_IC_ENABLE);
>  		if ((dw_readl(dev, DW_IC_ENABLE_STATUS) & 1) == enable)
> -- 
> 2.0.0.rc2
> 

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