gpio: aspeed: fix compile testing warning

Message ID 20180709145612.4166409-1-arnd@arndb.de
State New
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Series
  • gpio: aspeed: fix compile testing warning
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Commit Message

Arnd Bergmann July 9, 2018, 2:56 p.m.
Gcc cannot always see that BUG_ON(1) is guaranteed to not
return, so we get a warning message in some configurations:

drivers/gpio/gpio-aspeed.c: In function 'bank_reg':
drivers/gpio/gpio-aspeed.c:244:1: error: control reaches end of non-void function [-Werror=return-type]

Using a plain BUG() is easier here and avoids the problem.

Fixes: 44ddf559d579 ("gpio: aspeed: Rework register type accessors")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/gpio/gpio-aspeed.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Alexander Stein July 9, 2018, 3:31 p.m. | #1
On Monday, July 9, 2018, 4:56:03 PM CEST Arnd Bergmann wrote:
> Gcc cannot always see that BUG_ON(1) is guaranteed to not
> return, so we get a warning message in some configurations:
> 
> drivers/gpio/gpio-aspeed.c: In function 'bank_reg':
> drivers/gpio/gpio-aspeed.c:244:1: error: control reaches end of non-void
> function [-Werror=return-type]
> 
> Using a plain BUG() is easier here and avoids the problem.
> 
> Fixes: 44ddf559d579 ("gpio: aspeed: Rework register type accessors")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/gpio/gpio-aspeed.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpio/gpio-aspeed.c b/drivers/gpio/gpio-aspeed.c
> index 1e00f4045f9d..2342e154029b 100644
> --- a/drivers/gpio/gpio-aspeed.c
> +++ b/drivers/gpio/gpio-aspeed.c
> @@ -240,7 +240,7 @@ static inline void __iomem *bank_reg(struct aspeed_gpio
> *gpio, case reg_cmdsrc1:
>  		return gpio->base + bank->cmdsrc_regs + GPIO_CMDSRC_1;
>  	}
> -	BUG_ON(1);
> +	BUG();
>  }
> 
>  #define GPIO_BANK(x)	((x) >> 5)

Is the semantic of BUG() (and BUG_ON as well) to never return? If so, then 
just an idea: Is it possible to add some macro magic in BUG_ON(x) to fail 
compiling if x is compile-constant? Giving a hint the passed condition always 
fails, which indicates a problem, at least to me.
From a short search I found this in drivers/gpu/vga/vgaarb.c L630-633:
>	if (vgadev_find(pdev) != NULL) {
>		BUG_ON(1);
>		goto fail;
>	}
You can't fail with a BUG_ON(1) and try to do some error handling after that.

Best regards,
Alexander



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Arnd Bergmann July 9, 2018, 7:52 p.m. | #2
On Mon, Jul 9, 2018 at 5:31 PM, Alexander Stein
<alexander.stein@systec-electronic.com> wrote:
> On Monday, July 9, 2018, 4:56:03 PM CEST Arnd Bergmann wrote:
>> Gcc cannot always see that BUG_ON(1) is guaranteed to not
>> return, so we get a warning message in some configurations:
>>
>> drivers/gpio/gpio-aspeed.c: In function 'bank_reg':
>> drivers/gpio/gpio-aspeed.c:244:1: error: control reaches end of non-void
>> function [-Werror=return-type]
>>
>> Using a plain BUG() is easier here and avoids the problem.
>>
>> Fixes: 44ddf559d579 ("gpio: aspeed: Rework register type accessors")
>> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
>> ---
>>  drivers/gpio/gpio-aspeed.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpio/gpio-aspeed.c b/drivers/gpio/gpio-aspeed.c
>> index 1e00f4045f9d..2342e154029b 100644
>> --- a/drivers/gpio/gpio-aspeed.c
>> +++ b/drivers/gpio/gpio-aspeed.c
>> @@ -240,7 +240,7 @@ static inline void __iomem *bank_reg(struct aspeed_gpio
>> *gpio, case reg_cmdsrc1:
>>               return gpio->base + bank->cmdsrc_regs + GPIO_CMDSRC_1;
>>       }
>> -     BUG_ON(1);
>> +     BUG();
>>  }
>>
>>  #define GPIO_BANK(x) ((x) >> 5)
>
> Is the semantic of BUG() (and BUG_ON as well) to never return?

On most architectures and configurations yes, but not on some of
the minor architectures if CONFIG_BUG is disabled.

> If so, then
> just an idea: Is it possible to add some macro magic in BUG_ON(x) to fail
> compiling if x is compile-constant? Giving a hint the passed condition always
> fails, which indicates a problem, at least to me.

Not sure, that might not work well in cases where it's a compile-time
constant in some configurations but variable in others.

> From a short search I found this in drivers/gpu/vga/vgaarb.c L630-633:
>>       if (vgadev_find(pdev) != NULL) {
>>               BUG_ON(1);
>>               goto fail;
>>       }
> You can't fail with a BUG_ON(1) and try to do some error handling after that.

Right.

Traditionally when CONFIG_BUG was disabled, we would have continued
here, so that could have been intentional, but in any case a WARN_ON()
would have been more appropriate here.

      Arnd
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Benjamin Herrenschmidt July 9, 2018, 11:53 p.m. | #3
On Mon, 2018-07-09 at 16:56 +0200, Arnd Bergmann wrote:
> Gcc cannot always see that BUG_ON(1) is guaranteed to not
> return, so we get a warning message in some configurations:
> 
> drivers/gpio/gpio-aspeed.c: In function 'bank_reg':
> drivers/gpio/gpio-aspeed.c:244:1: error: control reaches end of non-void function [-Werror=return-type]
> 
> Using a plain BUG() is easier here and avoids the problem.
> 
> Fixes: 44ddf559d579 ("gpio: aspeed: Rework register type accessors")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

Linus, can you plonk that on top of the patches in that topic branch
you created ?

> ---
>  drivers/gpio/gpio-aspeed.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpio/gpio-aspeed.c b/drivers/gpio/gpio-aspeed.c
> index 1e00f4045f9d..2342e154029b 100644
> --- a/drivers/gpio/gpio-aspeed.c
> +++ b/drivers/gpio/gpio-aspeed.c
> @@ -240,7 +240,7 @@ static inline void __iomem *bank_reg(struct aspeed_gpio *gpio,
>  	case reg_cmdsrc1:
>  		return gpio->base + bank->cmdsrc_regs + GPIO_CMDSRC_1;
>  	}
> -	BUG_ON(1);
> +	BUG();
>  }
>  
>  #define GPIO_BANK(x)	((x) >> 5)


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Linus Walleij July 13, 2018, 7:05 a.m. | #4
On Mon, Jul 9, 2018 at 4:56 PM Arnd Bergmann <arnd@arndb.de> wrote:

> Gcc cannot always see that BUG_ON(1) is guaranteed to not
> return, so we get a warning message in some configurations:
>
> drivers/gpio/gpio-aspeed.c: In function 'bank_reg':
> drivers/gpio/gpio-aspeed.c:244:1: error: control reaches end of non-void function [-Werror=return-type]
>
> Using a plain BUG() is easier here and avoids the problem.
>
> Fixes: 44ddf559d579 ("gpio: aspeed: Rework register type accessors")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Patch applied with Benjamin's ACK.

Yours,
Linus Walleij
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Linus Walleij July 13, 2018, 7:06 a.m. | #5
On Tue, Jul 10, 2018 at 1:53 AM Benjamin Herrenschmidt
<benh@kernel.crashing.org> wrote:

> On Mon, 2018-07-09 at 16:56 +0200, Arnd Bergmann wrote:
> > Gcc cannot always see that BUG_ON(1) is guaranteed to not
> > return, so we get a warning message in some configurations:
> >
> > drivers/gpio/gpio-aspeed.c: In function 'bank_reg':
> > drivers/gpio/gpio-aspeed.c:244:1: error: control reaches end of non-void function [-Werror=return-type]
> >
> > Using a plain BUG() is easier here and avoids the problem.
> >
> > Fixes: 44ddf559d579 ("gpio: aspeed: Rework register type accessors")
> > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
>
> Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
>
> Linus, can you plonk that on top of the patches in that topic branch
> you created ?

I put it on top of my devel branch where I merged in the topic
branch.

As it's a fringe thing anyways I don't think we need to recreate the
topic branch for this.

Yours,
Linus Walleij
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Patch

diff --git a/drivers/gpio/gpio-aspeed.c b/drivers/gpio/gpio-aspeed.c
index 1e00f4045f9d..2342e154029b 100644
--- a/drivers/gpio/gpio-aspeed.c
+++ b/drivers/gpio/gpio-aspeed.c
@@ -240,7 +240,7 @@  static inline void __iomem *bank_reg(struct aspeed_gpio *gpio,
 	case reg_cmdsrc1:
 		return gpio->base + bank->cmdsrc_regs + GPIO_CMDSRC_1;
 	}
-	BUG_ON(1);
+	BUG();
 }
 
 #define GPIO_BANK(x)	((x) >> 5)