linux-kernel - Re: [PATCH] mailbox: imx: Fix clk handling in imx_mu

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Date:   Mon, 17 Dec 2018 07:01:11 +0100
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Alexey Khoroshilov <khoroshilov@...ras.ru>
Cc:     Jassi Brar <jassisinghbrar@...il.com>,
        linux-kernel@...r.kernel.org, ldv-project@...uxtesting.org
Subject: Re: [PATCH] mailbox: imx: Fix clk handling in imx_mu_probe()

Hi Alexey,

On Sun, Dec 16, 2018 at 02:01:44AM +0300, Alexey Khoroshilov wrote:
> Handling of devm_clk_get() suggests that the driver should support
> lack of priv->clk. But imx_mu_probe() fails on clk_prepare_enable(NULL)
> in that case.
> 
> The patch removes the try to enable absent clk and adds error handling
> for mbox_controller_register().
> 
> Found by Linux Driver Verification project (linuxtesting.org).
> 
> Signed-off-by: Alexey Khoroshilov <khoroshilov@...ras.ru>
> ---
>  drivers/mailbox/imx-mailbox.c | 18 +++++++++++++-----
>  1 file changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/mailbox/imx-mailbox.c b/drivers/mailbox/imx-mailbox.c
> index 363d35d5e49d..ddde398f576e 100644
> --- a/drivers/mailbox/imx-mailbox.c
> +++ b/drivers/mailbox/imx-mailbox.c
> @@ -292,10 +292,12 @@ static int imx_mu_probe(struct platform_device *pdev)
>  		priv->clk = NULL;
>  	}
>  
> -	ret = clk_prepare_enable(priv->clk);
> -	if (ret) {
> -		dev_err(dev, "Failed to enable clock\n");
> -		return ret;
> +	if (priv->clk) {
> +		ret = clk_prepare_enable(priv->clk);
> +		if (ret) {
> +			dev_err(dev, "Failed to enable clock\n");
> +			return ret;
> +		}
>  	}
>  
>  	for (i = 0; i < IMX_MU_CHANS; i++) {
> @@ -324,7 +326,13 @@ static int imx_mu_probe(struct platform_device *pdev)
>  
>  	imx_mu_init_generic(priv);
>  
> -	return mbox_controller_register(&priv->mbox);
> +	ret = mbox_controller_register(&priv->mbox);
> +	if (ret) {
> +		clk_disable_unprepare(priv->clk);
> +		return ret;
> +	}
> +
> +	return 0;
>  }
>  
>  static int imx_mu_remove(struct platform_device *pdev)
> -- 
> 2.7.4
> 
> 

NACK for this patch.

Here are code snippets from clk framework:
============================================================================
/* clk_prepare_enable helps cases using clk_enable in non-atomic context. */
static inline int clk_prepare_enable(struct clk *clk)
{
	int ret;

	ret = clk_prepare(clk);
	if (ret)
		return ret;
	ret = clk_enable(clk);
	if (ret)
		clk_unprepare(clk);

	return ret;
}

int clk_prepare(struct clk *clk)
{
	if (!clk)
		return 0;

	return clk_core_prepare_lock(clk->core);
}

int clk_enable(struct clk *clk)
{
	if (!clk)
		return 0;

	return clk_core_enable_lock(clk->core);
}
============================================================================

As you can see, complete code path is NULL resistant. Are you trying to
fix some real issue, or it is a theoretical work?

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