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

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Message-ID: <3ccce5b6-75a5-da94-08e3-985880382d00@ispras.ru>
Date:   Mon, 17 Dec 2018 10:24:00 +0300
From:   Alexey Khoroshilov <khoroshilov@...ras.ru>
To:     Oleksij Rempel <o.rempel@...gutronix.de>
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 Oleksij,

By chance I took a look at another implementations:

arch/arm/mach-ep93xx/clock.c#L266

int clk_enable(struct clk *clk)
{
	unsigned long flags;

	if (!clk)
		return -EINVAL;
...

arch/c6x/platforms/pll.c#L48

int clk_enable(struct clk *clk)
{
	unsigned long flags;

	if (clk == NULL || IS_ERR(clk))
		return -EINVAL;

So, I am not sure the NULL resistance is a part of the clk_enable()
contract?

--
Alexey


On 17.12.2018 9:01, Oleksij Rempel wrote:
> 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?
>