linux-kernel - Re: [PATCH v4 07/16] PM / devfreq: tegra: Properly disable interrupts

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Message-ID: <20190604110744.GG16519@ulmo>
Date:   Tue, 4 Jun 2019 13:07:44 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Jonathan Hunter <jonathanh@...dia.com>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        linux-pm@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 07/16] PM / devfreq: tegra: Properly disable interrupts

On Thu, May 02, 2019 at 02:38:06AM +0300, Dmitry Osipenko wrote:
> There is no guarantee that interrupt handling isn't running in parallel
> with tegra_actmon_disable_interrupts(), hence it is necessary to protect
> DEV_CTRL register accesses and clear IRQ status with ACTMON's IRQ being
> disabled in the Interrupt Controller in order to ensure that device
> interrupt is indeed being disabled.
> 
> Reviewed-by: Chanwoo Choi <cw00.choi@...sung.com>
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>  drivers/devfreq/tegra-devfreq.c | 21 +++++++++++++++------
>  1 file changed, 15 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/devfreq/tegra-devfreq.c b/drivers/devfreq/tegra-devfreq.c
> index b65313fe3c2e..ce1eb97a2090 100644
> --- a/drivers/devfreq/tegra-devfreq.c
> +++ b/drivers/devfreq/tegra-devfreq.c
> @@ -171,6 +171,8 @@ struct tegra_devfreq {
>  	struct notifier_block	rate_change_nb;
>  
>  	struct tegra_devfreq_device devices[ARRAY_SIZE(actmon_device_configs)];
> +
> +	int irq;

Interrupts are typically unsigned int.

>  };
>  
>  struct tegra_actmon_emc_ratio {
> @@ -417,6 +419,8 @@ static void tegra_actmon_disable_interrupts(struct tegra_devfreq *tegra)
>  	u32 val;
>  	unsigned int i;
>  
> +	disable_irq(tegra->irq);
> +
>  	for (i = 0; i < ARRAY_SIZE(tegra->devices); i++) {
>  		dev = &tegra->devices[i];
>  
> @@ -427,9 +431,14 @@ static void tegra_actmon_disable_interrupts(struct tegra_devfreq *tegra)
>  		val &= ~ACTMON_DEV_CTRL_CONSECUTIVE_ABOVE_WMARK_EN;
>  
>  		device_writel(dev, val, ACTMON_DEV_CTRL);
> +
> +		device_writel(dev, ACTMON_INTR_STATUS_CLEAR,
> +			      ACTMON_DEV_INTR_STATUS);
>  	}
>  
>  	actmon_write_barrier(tegra);
> +
> +	enable_irq(tegra->irq);

Why do we enable interrupts after this? Is there any use in having the
top-level interrupt enabled if nothing's going to generate an interrupt
anyway?

>  }
>  
>  static void tegra_actmon_configure_device(struct tegra_devfreq *tegra,
> @@ -604,7 +613,6 @@ static int tegra_devfreq_probe(struct platform_device *pdev)
>  	struct resource *res;
>  	unsigned int i;
>  	unsigned long rate;
> -	int irq;
>  	int err;
>  
>  	tegra = devm_kzalloc(&pdev->dev, sizeof(*tegra), GFP_KERNEL);
> @@ -673,15 +681,16 @@ static int tegra_devfreq_probe(struct platform_device *pdev)
>  		dev_pm_opp_add(&pdev->dev, rate, 0);
>  	}
>  
> -	irq = platform_get_irq(pdev, 0);
> -	if (irq < 0) {
> -		dev_err(&pdev->dev, "Failed to get IRQ: %d\n", irq);
> -		return irq;
> +	tegra->irq = platform_get_irq(pdev, 0);
> +	if (tegra->irq < 0) {
> +		err = tegra->irq;
> +		dev_err(&pdev->dev, "Failed to get IRQ: %d\n", err);
> +		return err;
>  	}

This is very oddly written. tegra->irq should really be an unsigned int
since that's the standard type for interrupt numbers. But since you need
to be able to detect errors from platform_get_irq() it now becomes
natural to write this as:

	err = platform_get_irq(pdev, 0);
	if (err < 0) {
		dev_err(...);
		return err;
	}

	tegra->irq = err;

Two birds with one stone. I suppose this could be done in a follow-up
patch since it isn't practically wrong in your version, so either way:

Acked-by: Thierry Reding <treding@...dia.com>

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