diff mbox

[PATCHv2,1/5] clk: samsung: exynos5410: Add NULL pointer checks in clock init

Message ID 1406805732-17372-2-git-send-email-hsnaves@gmail.com
State Superseded
Headers show

Commit Message

Humberto Naves July 31, 2014, 11:22 a.m. UTC
Added NULL pointer checks for device_node input parameter and
for the samsung_clk_provider context returned by samsung_clk_init.
Even though the *current* samsung_clk_init function never returns
a NULL pointer, it is good to keep this check in place to avoid
possible problems in the future due to changes in implementation.
That way, we also improve the consistency of the code that performs
clock initialization across the different SoCs.

Signed-off-by: Humberto Silva Naves <hsnaves@gmail.com>
---
 drivers/clk/samsung/clk-exynos5410.c |   12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

Comments

Tomasz Figa July 31, 2014, 12:34 p.m. UTC | #1
Hi Humberto,

Please see my comments inline.

On 31.07.2014 13:22, Humberto Silva Naves wrote:
> Added NULL pointer checks for device_node input parameter and
> for the samsung_clk_provider context returned by samsung_clk_init.
> Even though the *current* samsung_clk_init function never returns
> a NULL pointer, it is good to keep this check in place to avoid
> possible problems in the future due to changes in implementation.
> That way, we also improve the consistency of the code that performs
> clock initialization across the different SoCs.
> 
> Signed-off-by: Humberto Silva Naves <hsnaves@gmail.com>
> ---
>  drivers/clk/samsung/clk-exynos5410.c |   12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/clk/samsung/clk-exynos5410.c b/drivers/clk/samsung/clk-exynos5410.c
> index 231475b..bf57c80 100644
> --- a/drivers/clk/samsung/clk-exynos5410.c
> +++ b/drivers/clk/samsung/clk-exynos5410.c
> @@ -188,11 +188,17 @@ static void __init exynos5410_clk_init(struct device_node *np)
>  	struct samsung_clk_provider *ctx;
>  	void __iomem *reg_base;
>  
> -	reg_base = of_iomap(np, 0);
> -	if (!reg_base)
> -		panic("%s: failed to map registers\n", __func__);
> +	if (np) {

Since all Exynos-based boards are always booted using DT, this function
will never be called if there is no node for the clock controller and so
there is no way this pointer can end up being NULL. I don't see a point
in complicating this code with useless checks.

> +		reg_base = of_iomap(np, 0);
> +		if (!reg_base)
> +			panic("%s: failed to map registers\n", __func__);
> +	} else {
> +		panic("%s: unable to determine soc\n", __func__);
> +	}

As a side note, since panic() does not return, the code above could be
changed to follow rest of checks in this function:

	if (!np)
		panic("%s: unable to determine soc\n", __func__);

	reg_base = of_iomap(np, 0);
	...

leading to more readable code with less indentation and less changes to
existing code.

>  
>  	ctx = samsung_clk_init(np, reg_base, CLK_NR_CLKS);
> +	if (!ctx)
> +		panic("%s: unable to allocate context.\n", __func__);

samsung_clk_init() already panics on any error, although now as I think
of it, it probably should be changed with a patch to just error out and
let the caller handle the error. However callers don't need to be
changed before this is done.

Best regards,
Tomasz
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Humberto Naves July 31, 2014, 1:13 p.m. UTC | #2
Hi,

I am bit confused by your response: first you mentioned that I should
remove the NULL check for variable np, but later on you suggested that
I should rearrange the conditional statement to avoid adding more
indentation. My guess is that I should remove that if statement
altogether?

Regarding the ctx variable, should I still remove the NULL check? As
you said, in the near future samsung_clk_init() won't panic anymore,
and keeping the check in place won't hurt anybody.

Best,
Humberto

On Thu, Jul 31, 2014 at 2:34 PM, Tomasz Figa <tomasz.figa@gmail.com> wrote:
> Hi Humberto,
>
> Please see my comments inline.
>
> On 31.07.2014 13:22, Humberto Silva Naves wrote:
>> Added NULL pointer checks for device_node input parameter and
>> for the samsung_clk_provider context returned by samsung_clk_init.
>> Even though the *current* samsung_clk_init function never returns
>> a NULL pointer, it is good to keep this check in place to avoid
>> possible problems in the future due to changes in implementation.
>> That way, we also improve the consistency of the code that performs
>> clock initialization across the different SoCs.
>>
>> Signed-off-by: Humberto Silva Naves <hsnaves@gmail.com>
>> ---
>>  drivers/clk/samsung/clk-exynos5410.c |   12 +++++++++---
>>  1 file changed, 9 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/clk/samsung/clk-exynos5410.c b/drivers/clk/samsung/clk-exynos5410.c
>> index 231475b..bf57c80 100644
>> --- a/drivers/clk/samsung/clk-exynos5410.c
>> +++ b/drivers/clk/samsung/clk-exynos5410.c
>> @@ -188,11 +188,17 @@ static void __init exynos5410_clk_init(struct device_node *np)
>>       struct samsung_clk_provider *ctx;
>>       void __iomem *reg_base;
>>
>> -     reg_base = of_iomap(np, 0);
>> -     if (!reg_base)
>> -             panic("%s: failed to map registers\n", __func__);
>> +     if (np) {
>
> Since all Exynos-based boards are always booted using DT, this function
> will never be called if there is no node for the clock controller and so
> there is no way this pointer can end up being NULL. I don't see a point
> in complicating this code with useless checks.
>
>> +             reg_base = of_iomap(np, 0);
>> +             if (!reg_base)
>> +                     panic("%s: failed to map registers\n", __func__);
>> +     } else {
>> +             panic("%s: unable to determine soc\n", __func__);
>> +     }
>
> As a side note, since panic() does not return, the code above could be
> changed to follow rest of checks in this function:
>
>         if (!np)
>                 panic("%s: unable to determine soc\n", __func__);
>
>         reg_base = of_iomap(np, 0);
>         ...
>
> leading to more readable code with less indentation and less changes to
> existing code.
>
>>
>>       ctx = samsung_clk_init(np, reg_base, CLK_NR_CLKS);
>> +     if (!ctx)
>> +             panic("%s: unable to allocate context.\n", __func__);
>
> samsung_clk_init() already panics on any error, although now as I think
> of it, it probably should be changed with a patch to just error out and
> let the caller handle the error. However callers don't need to be
> changed before this is done.
>
> Best regards,
> Tomasz
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Tomasz Figa July 31, 2014, 1:20 p.m. UTC | #3
On 31.07.2014 15:13, Humberto Naves wrote:
> Hi,
> 
> I am bit confused by your response: first you mentioned that I should
> remove the NULL check for variable np, but later on you suggested that
> I should rearrange the conditional statement to avoid adding more
> indentation.

That was just a side note.

> My guess is that I should remove that if statement
> altogether?

Yes, that was my intention.

> 
> Regarding the ctx variable, should I still remove the NULL check? As
> you said, in the near future samsung_clk_init() won't panic anymore,
> and keeping the check in place won't hurt anybody.

The rule of thumb for kernel patches is that we want a patch if we know
that it is something we need. We don't know yet when and how (which
error returning convention, NULL or ERR_PTR() or maybe something else?)
samsung_clk_init() gets changed, so right now we shouldn't change its
callers.

Of course a patch changing samsung_clk_init() and all its callers in one
go will be welcome.

By the way, please avoid top posting. Here's a good read on Linux
mailing lists netiquette: http://www.tux.org/lkml/#s3 .

Best regards,
Tomasz

> 
> Best,
> Humberto
> 
> On Thu, Jul 31, 2014 at 2:34 PM, Tomasz Figa <tomasz.figa@gmail.com> wrote:
>> Hi Humberto,
>>
>> Please see my comments inline.
>>
>> On 31.07.2014 13:22, Humberto Silva Naves wrote:
>>> Added NULL pointer checks for device_node input parameter and
>>> for the samsung_clk_provider context returned by samsung_clk_init.
>>> Even though the *current* samsung_clk_init function never returns
>>> a NULL pointer, it is good to keep this check in place to avoid
>>> possible problems in the future due to changes in implementation.
>>> That way, we also improve the consistency of the code that performs
>>> clock initialization across the different SoCs.
>>>
>>> Signed-off-by: Humberto Silva Naves <hsnaves@gmail.com>
>>> ---
>>>  drivers/clk/samsung/clk-exynos5410.c |   12 +++++++++---
>>>  1 file changed, 9 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/clk/samsung/clk-exynos5410.c b/drivers/clk/samsung/clk-exynos5410.c
>>> index 231475b..bf57c80 100644
>>> --- a/drivers/clk/samsung/clk-exynos5410.c
>>> +++ b/drivers/clk/samsung/clk-exynos5410.c
>>> @@ -188,11 +188,17 @@ static void __init exynos5410_clk_init(struct device_node *np)
>>>       struct samsung_clk_provider *ctx;
>>>       void __iomem *reg_base;
>>>
>>> -     reg_base = of_iomap(np, 0);
>>> -     if (!reg_base)
>>> -             panic("%s: failed to map registers\n", __func__);
>>> +     if (np) {
>>
>> Since all Exynos-based boards are always booted using DT, this function
>> will never be called if there is no node for the clock controller and so
>> there is no way this pointer can end up being NULL. I don't see a point
>> in complicating this code with useless checks.
>>
>>> +             reg_base = of_iomap(np, 0);
>>> +             if (!reg_base)
>>> +                     panic("%s: failed to map registers\n", __func__);
>>> +     } else {
>>> +             panic("%s: unable to determine soc\n", __func__);
>>> +     }
>>
>> As a side note, since panic() does not return, the code above could be
>> changed to follow rest of checks in this function:
>>
>>         if (!np)
>>                 panic("%s: unable to determine soc\n", __func__);
>>
>>         reg_base = of_iomap(np, 0);
>>         ...
>>
>> leading to more readable code with less indentation and less changes to
>> existing code.
>>
>>>
>>>       ctx = samsung_clk_init(np, reg_base, CLK_NR_CLKS);
>>> +     if (!ctx)
>>> +             panic("%s: unable to allocate context.\n", __func__);
>>
>> samsung_clk_init() already panics on any error, although now as I think
>> of it, it probably should be changed with a patch to just error out and
>> let the caller handle the error. However callers don't need to be
>> changed before this is done.
>>
>> Best regards,
>> Tomasz
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diff mbox

Patch

diff --git a/drivers/clk/samsung/clk-exynos5410.c b/drivers/clk/samsung/clk-exynos5410.c
index 231475b..bf57c80 100644
--- a/drivers/clk/samsung/clk-exynos5410.c
+++ b/drivers/clk/samsung/clk-exynos5410.c
@@ -188,11 +188,17 @@  static void __init exynos5410_clk_init(struct device_node *np)
 	struct samsung_clk_provider *ctx;
 	void __iomem *reg_base;
 
-	reg_base = of_iomap(np, 0);
-	if (!reg_base)
-		panic("%s: failed to map registers\n", __func__);
+	if (np) {
+		reg_base = of_iomap(np, 0);
+		if (!reg_base)
+			panic("%s: failed to map registers\n", __func__);
+	} else {
+		panic("%s: unable to determine soc\n", __func__);
+	}
 
 	ctx = samsung_clk_init(np, reg_base, CLK_NR_CLKS);
+	if (!ctx)
+		panic("%s: unable to allocate context.\n", __func__);
 
 	samsung_clk_register_pll(ctx, exynos5410_plls,
 			ARRAY_SIZE(exynos5410_plls), reg_base);