linux-kernel - Re: [PATCH v2] mfd: qcom_rpm: handle message RAM clock

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Message-ID: <20160818192241.GW26240@tuxbot>
Date:   Thu, 18 Aug 2016 12:22:41 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     lee.jones@...aro.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mfd: qcom_rpm: handle message RAM clock

On Thu 18 Aug 11:40 PDT 2016, Linus Walleij wrote:

> The MSM8660, APQ8060, IPQ806x and MSM8960 have a GCC clock
> to the message RAM used by the RPM. This needs to be enabled
> for messages to pass through. This is a crude solution that
> simply prepare/enable at probe() and disable/unprepare
> at remove(). More elaborate PM is probably possible to
> add later.
> 
> The construction uses IS_ERR() to gracefully handle the
> platforms that do not provide a message RAM clock. It will
> bail out of probe only if the clock is hitting a probe
> deferral situation.
> 
> Of course this requires the proper device tree set-up:
> 
> rpm: rpm@...000 {
>     compatible = "qcom,rpm-msm8660";
>     clocks = <&gcc RPM_MSG_RAM_H_CLK>;
>     clock-names = "ram";
>     ...
> };
> 
> I have provided this in the MSM8660 device tree, and will
> provide patches for the other targets.
> 
> Cc: Björn Andersson <bjorn.andersson@...aro.org>
> Signed-off-by: Linus Walleij <linus.walleij@...aro.org>

Acked-by: Bjorn Andersson <bjorn.andersson@...aro.org>

Regards,
Bjorn

> ---
> ChangeLog v1->v2:
> - Exploit that a clk can be NULL and handled transparently
>   by the clock framework, simplifying the code
> - Move clock disablement after the OF depopulation call
> ---
>  drivers/mfd/qcom_rpm.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/drivers/mfd/qcom_rpm.c b/drivers/mfd/qcom_rpm.c
> index 2e44323455dd..315da71bde49 100644
> --- a/drivers/mfd/qcom_rpm.c
> +++ b/drivers/mfd/qcom_rpm.c
> @@ -21,6 +21,7 @@
>  #include <linux/mfd/qcom_rpm.h>
>  #include <linux/mfd/syscon.h>
>  #include <linux/regmap.h>
> +#include <linux/clk.h>
>  
>  #include <dt-bindings/mfd/qcom-rpm.h>
>  
> @@ -48,6 +49,7 @@ struct qcom_rpm {
>  	struct regmap *ipc_regmap;
>  	unsigned ipc_offset;
>  	unsigned ipc_bit;
> +	struct clk *ramclk;
>  
>  	struct completion ack;
>  	struct mutex lock;
> @@ -501,6 +503,20 @@ static int qcom_rpm_probe(struct platform_device *pdev)
>  	mutex_init(&rpm->lock);
>  	init_completion(&rpm->ack);
>  
> +	/* Enable message RAM clock */
> +	rpm->ramclk = devm_clk_get(&pdev->dev, "ram");
> +	if (IS_ERR(rpm->ramclk)) {
> +		ret = PTR_ERR(rpm->ramclk);
> +		if (ret == -EPROBE_DEFER)
> +			return ret;
> +		/*
> +		 * Fall through in all other cases, as the clock is
> +		 * optional. (Does not exist on all platforms.)
> +		 */
> +		rpm->ramclk = NULL;
> +	}
> +	clk_prepare_enable(rpm->ramclk); /* Accepts NULL */
> +
>  	irq_ack = platform_get_irq_byname(pdev, "ack");
>  	if (irq_ack < 0) {
>  		dev_err(&pdev->dev, "required ack interrupt missing\n");
> @@ -620,7 +636,11 @@ static int qcom_rpm_probe(struct platform_device *pdev)
>  
>  static int qcom_rpm_remove(struct platform_device *pdev)
>  {
> +	struct qcom_rpm *rpm = dev_get_drvdata(&pdev->dev);
> +
>  	of_platform_depopulate(&pdev->dev);
> +	clk_disable_unprepare(rpm->ramclk);
> +
>  	return 0;
>  }
>  
> -- 
> 2.7.4
>