linux-kernel - Re: [PATCH] mfd: twl6040: Optional clk32k clock handling

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Message-ID: <20140428103629.GI21279@lee--X1>
Date:	Mon, 28 Apr 2014 11:36:29 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	Peter Ujfalusi <peter.ujfalusi@...com>
Cc:	sameo@...ux.intel.com, devicetree@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mfd: twl6040: Optional clk32k clock handling

> In certain boards the source for the clk32k clock can be gated. In these
> boards the clk32k clock can be provided to the driver and it is going to be
> enabled/disabled when it is needed.
> If the clk32k clock is not provided the driver will assume that it is always
> running.
> 
> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@...com>
> ---
>  Documentation/devicetree/bindings/mfd/twl6040.txt |  2 ++
>  drivers/mfd/twl6040.c                             | 10 ++++++++++
>  include/linux/mfd/twl6040.h                       |  2 ++
>  3 files changed, 14 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/mfd/twl6040.txt b/Documentation/devicetree/bindings/mfd/twl6040.txt
> index 0f5dd709d752..a41157b5d930 100644
> --- a/Documentation/devicetree/bindings/mfd/twl6040.txt
> +++ b/Documentation/devicetree/bindings/mfd/twl6040.txt
> @@ -19,6 +19,8 @@ Required properties:
>  
>  Optional properties, nodes:
>  - enable-active-high: To power on the twl6040 during boot.
> +- clocks: phandle to the clk32k clock provider
> +- clock-names: Must be "clk32k"
>  
>  Vibra functionality
>  Required properties:
> diff --git a/drivers/mfd/twl6040.c b/drivers/mfd/twl6040.c
> index 2e6504a8e1e3..12b314ea48dc 100644
> --- a/drivers/mfd/twl6040.c
> +++ b/drivers/mfd/twl6040.c
> @@ -291,6 +291,8 @@ int twl6040_power(struct twl6040 *twl6040, int on)
>  		if (twl6040->power_count++)
>  			goto out;
>  
> +		clk_prepare_enable(twl6040->clk32k);
> +
>  		/* Allow writes to the chip */
>  		regcache_cache_only(twl6040->regmap, false);
>  
> @@ -346,6 +348,8 @@ int twl6040_power(struct twl6040 *twl6040, int on)
>  
>  		twl6040->sysclk = 0;
>  		twl6040->mclk = 0;
> +
> +		clk_disable_unprepare(twl6040->clk32k);
>  	}
>  
>  out:
> @@ -644,6 +648,12 @@ static int twl6040_probe(struct i2c_client *client,
>  
>  	i2c_set_clientdata(client, twl6040);
>  
> +	twl6040->clk32k = devm_clk_get(&client->dev, "clk32k");
> +	if (IS_ERR(twl6040->clk32k)) {
> +		dev_info(&client->dev, "clk32k is not handled\n");
> +		twl6040->clk32k = NULL;

So what happens if you pass a NULL clk reference to clk_prepare_enable()?

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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