linux-kernel - Re: [PATCH v3 2/2] i2c: designware: Add support for a bus clock

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Date:   Wed, 20 Feb 2019 20:55:48 +0100
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Gareth Williams <gareth.williams.jx@...esas.com>
Cc:     Jarkko Nikula <jarkko.nikula@...ux.intel.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        linux-i2c@...r.kernel.org,
        Phil Edworthy <phil.edworthy@...esas.com>,
        linux-kernel@...r.kernel.org, linux-renesas-soc@...r.kernel.org
Subject: Re: [PATCH v3 2/2] i2c: designware: Add support for a bus clock

On Wed, Feb 20, 2019 at 03:50:03PM +0000, Gareth Williams wrote:
> From: Phil Edworthy <phil.edworthy@...esas.com>
> 
> The Synopsys I2C Controller has a bus clock, but most SoCs hide this away.
> However, on some SoCs you need to explicity enable the bus clock in order
> to access the registers. Therefore, add support for an optional bus clock.
> 
> Signed-off-by: Phil Edworthy <phil.edworthy@...esas.com>
> Signed-off-by: Gareth Williams <gareth.williams.jx@...esas.com>

Code looks good to me. For clarity, though, s/bus clock/peripheral
clock/ in the commit message and code comments.

After that:

Acked-by: Wolfram Sang <wsa+renesas@...g-engineering.com>

> ---
> v3:
>  - busclk renamed to pclk.
>  - Added comment with dw_i2c_dev struct definition describing pclk.
>  - Added enable rollback of first clock if second fails to enable.
> v2:
>  - Use new devm_clk_get_optional() function as it simplifies handling when
>    the optional clock is not present.
> ---
>  drivers/i2c/busses/i2c-designware-common.c  | 18 ++++++++++++++++--
>  drivers/i2c/busses/i2c-designware-core.h    |  2 ++
>  drivers/i2c/busses/i2c-designware-platdrv.c |  5 +++++
>  3 files changed, 23 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-designware-common.c b/drivers/i2c/busses/i2c-designware-common.c
> index a473011..5f70078 100644
> --- a/drivers/i2c/busses/i2c-designware-common.c
> +++ b/drivers/i2c/busses/i2c-designware-common.c
> @@ -251,13 +251,27 @@ unsigned long i2c_dw_clk_rate(struct dw_i2c_dev *dev)
>  
>  int i2c_dw_prepare_clk(struct dw_i2c_dev *dev, bool prepare)
>  {
> +	int ret;
> +
>  	if (IS_ERR(dev->clk))
>  		return PTR_ERR(dev->clk);
>  
> -	if (prepare)
> -		return clk_prepare_enable(dev->clk);
> +	if (prepare) {
> +		/* Optional bus clock */
> +		ret = clk_prepare_enable(dev->pclk);
> +		if (ret)
> +			return ret;
> +
> +		ret = clk_prepare_enable(dev->clk);
> +		if (ret)
> +			clk_disable_unprepare(dev->pclk);
> +
> +		return ret;
> +	}
>  
>  	clk_disable_unprepare(dev->clk);
> +	clk_disable_unprepare(dev->pclk);
> +
>  	return 0;
>  }
>  EXPORT_SYMBOL_GPL(i2c_dw_prepare_clk);
> diff --git a/drivers/i2c/busses/i2c-designware-core.h b/drivers/i2c/busses/i2c-designware-core.h
> index b4a0b2b..e88c711 100644
> --- a/drivers/i2c/busses/i2c-designware-core.h
> +++ b/drivers/i2c/busses/i2c-designware-core.h
> @@ -177,6 +177,7 @@
>   * @base: IO registers pointer
>   * @cmd_complete: tx completion indicator
>   * @clk: input reference clock
> + * @pclk: clock required to access the registers
>   * @slave: represent an I2C slave device
>   * @cmd_err: run time hadware error code
>   * @msgs: points to an array of messages currently being transferred
> @@ -226,6 +227,7 @@ struct dw_i2c_dev {
>  	void __iomem		*ext;
>  	struct completion	cmd_complete;
>  	struct clk		*clk;
> +	struct clk		*pclk;
>  	struct reset_control	*rst;
>  	struct i2c_client		*slave;
>  	u32			(*get_clk_rate_khz) (struct dw_i2c_dev *dev);
> diff --git a/drivers/i2c/busses/i2c-designware-platdrv.c b/drivers/i2c/busses/i2c-designware-platdrv.c
> index 9eaac3b..c550fb2 100644
> --- a/drivers/i2c/busses/i2c-designware-platdrv.c
> +++ b/drivers/i2c/busses/i2c-designware-platdrv.c
> @@ -346,6 +346,11 @@ static int dw_i2c_plat_probe(struct platform_device *pdev)
>  	else
>  		i2c_dw_configure_master(dev);
>  
> +	/* Optional bus clock */
> +	dev->pclk = devm_clk_get_optional(&pdev->dev, "pclk");
> +	if (IS_ERR(dev->pclk))
> +		return PTR_ERR(dev->pclk);
> +
>  	dev->clk = devm_clk_get(&pdev->dev, NULL);
>  	if (!i2c_dw_prepare_clk(dev, true)) {
>  		u64 clk_khz;
> -- 
> 2.7.4
> 

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