linux-kernel - Re: [PATCH v3] i2c: ocores: use devm

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Date:   Wed, 24 May 2023 21:21:56 +0200
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Wang Zhang <silver_code@...t.edu.cn>,
        Peter Korsgaard <peter@...sgaard.com>,
        Andrew Lunn <andrew@...n.ch>
Cc:     hust-os-kernel-patches@...glegroups.com, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Dan Carpenter <dan.carpenter@...aro.org>
Subject: Re: [PATCH v3] i2c: ocores: use devm_ managed clks

Le 24/05/2023 à 17:43, Wang Zhang a écrit :
> While it is not entirely clear why the original author implemented this
> behavior, there may have been certain circumstances or issues that were not
> apparent to us. It's possible that they were trying to work around a bug by
> employing an unconventional solution.Using `devm_clk_get_enabled()` rather
> than devm_clk_get() can automatically track the usage of clocks and free
> them when they are no longer needed or an error occurs.
> 
> fixing it by changing `ocores_i2c_of_probe` to use
> `devm_clk_get_optional_enabled()` rather than `devm_clk_get()`, changing
> `goto err_clk' to direct return and removing `err_clk`.
> 
> Signed-off-by: Wang Zhang <silver_code@...t.edu.cn>
> Reviewed-by: Andrew Lunn <andrew@...n.ch>
> ---
> v2->v3: use `devm_clk_get_optional_enabled()` to manage clks
> v1->v2: change `ocores_i2c_of_probe` to use `devm_clk_get_enabled()`
> ---
>   drivers/i2c/busses/i2c-ocores.c | 57 +++++++++++++--------------------
>   1 file changed, 22 insertions(+), 35 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-ocores.c b/drivers/i2c/busses/i2c-ocores.c
> index 2e575856c5cd..316d72cde3b9 100644
> --- a/drivers/i2c/busses/i2c-ocores.c
> +++ b/drivers/i2c/busses/i2c-ocores.c
> @@ -552,16 +552,14 @@ static int ocores_i2c_of_probe(struct platform_device *pdev,
>   							&clock_frequency);
>   	i2c->bus_clock_khz = 100;
>   
> -	i2c->clk = devm_clk_get(&pdev->dev, NULL);
> +	i2c->clk = devm_clk_get_optional_enabled(&pdev->dev, NULL);
>   
> -	if (!IS_ERR(i2c->clk)) {
> -		int ret = clk_prepare_enable(i2c->clk);
> -
> -		if (ret) {
> -			dev_err(&pdev->dev,
> -				"clk_prepare_enable failed: %d\n", ret);
> -			return ret;
> -		}
> +	if (IS_ERR(i2c->clk)) {
> +		dev_err(&pdev->dev,
> +			"devm_clk_get_optional_enabled failed\n");

Maybe dev_err_probe() would be nice here. This would log the error code, 
and filter -EPROBE_DEFER, should it happen.

> +		return PTR_ERR(i2c->clk);
> +	}
> +	if (i2c->clk) {
>   		i2c->ip_clock_khz = clk_get_rate(i2c->clk) / 1000;
>   		if (clock_frequency_present)
>   			i2c->bus_clock_khz = clock_frequency / 1000;
> @@ -573,7 +571,6 @@ static int ocores_i2c_of_probe(struct platform_device *pdev,
>   			if (!clock_frequency_present) {
>   				dev_err(&pdev->dev,
>   					"Missing required parameter 'opencores,ip-clock-frequency'\n");
> -				clk_disable_unprepare(i2c->clk);
>   				return -ENODEV;
>   			}
>   			i2c->ip_clock_khz = clock_frequency / 1000;
> @@ -678,8 +675,7 @@ static int ocores_i2c_probe(struct platform_device *pdev)
>   		default:
>   			dev_err(&pdev->dev, "Unsupported I/O width (%d)\n",
>   				i2c->reg_io_width);
> -			ret = -EINVAL;
> -			goto err_clk;
> +			return -EINVAL;
>   		}
>   	}
>   
> @@ -710,13 +706,13 @@ static int ocores_i2c_probe(struct platform_device *pdev)
>   						   pdev->name, i2c);
>   		if (ret) {
>   			dev_err(&pdev->dev, "Cannot claim IRQ\n");
> -			goto err_clk;
> +			return ret;
>   		}
>   	}
>   
>   	ret = ocores_init(&pdev->dev, i2c);
>   	if (ret)
> -		goto err_clk;
> +		return ret;
>   
>   	/* hook up driver to tree */
>   	platform_set_drvdata(pdev, i2c);
> @@ -728,7 +724,7 @@ static int ocores_i2c_probe(struct platform_device *pdev)
>   	/* add i2c adapter to i2c tree */
>   	ret = i2c_add_adapter(&i2c->adap);
>   	if (ret)
> -		goto err_clk;
> +		return ret;
>   
>   	/* add in known devices to the bus */
>   	if (pdata) {
> @@ -737,10 +733,6 @@ static int ocores_i2c_probe(struct platform_device *pdev)
>   	}
>   
>   	return 0;
> -
> -err_clk:
> -	clk_disable_unprepare(i2c->clk);
> -	return ret;
>   }
>   
>   static int ocores_i2c_remove(struct platform_device *pdev)
> @@ -755,9 +747,6 @@ static int ocores_i2c_remove(struct platform_device *pdev)
>   	/* remove adapter & data */
>   	i2c_del_adapter(&i2c->adap);
>   
> -	if (!IS_ERR(i2c->clk))
> -		clk_disable_unprepare(i2c->clk);
> -
>   	return 0;
>   }
>   
> @@ -771,8 +760,7 @@ static int ocores_i2c_suspend(struct device *dev)
>   	ctrl &= ~(OCI2C_CTRL_EN | OCI2C_CTRL_IEN);
>   	oc_setreg(i2c, OCI2C_CONTROL, ctrl);
>   
> -	if (!IS_ERR(i2c->clk))
> -		clk_disable_unprepare(i2c->clk);
> +	clk_disable_unprepare(i2c->clk);
>   	return 0;
>   }
>   
> @@ -780,19 +768,18 @@ static int ocores_i2c_resume(struct device *dev)
>   {
>   	struct ocores_i2c *i2c = dev_get_drvdata(dev);
>   
> -	if (!IS_ERR(i2c->clk)) {
> -		unsigned long rate;
> -		int ret = clk_prepare_enable(i2c->clk);
> +	unsigned long rate;
> +	int ret = clk_prepare_enable(i2c->clk);
>   
> -		if (ret) {
> -			dev_err(dev,
> -				"clk_prepare_enable failed: %d\n", ret);
> -			return ret;
> -		}
> -		rate = clk_get_rate(i2c->clk) / 1000;
> -		if (rate)
> -			i2c->ip_clock_khz = rate;
> +	if (ret) {
> +		dev_err(dev,
> +			"clk_prepare_enable failed: %d\n", ret);
> +		return ret;
>   	}
> +	rate = clk_get_rate(i2c->clk) / 1000;

Now (because of the devm_clk_get_optional_enabled()), i2c->clk can be 
NULL, so this would deference a NULL pointer.

CJ


> +	if (rate)
> +		i2c->ip_clock_khz = rate;
> +
>   	return ocores_init(dev, i2c);
>   }
>