[PATCH 1/1 linux-next] ACPI / SBS: fix sparse warning

[PATCH 1/1 linux-next] ACPI / SBS: fix sparse warning

[Fabian Frederick]

Adding parentheses around expression to avoid:
drivers/acpi/sbs.c:444:28: warning: dubious: !x & y

Signed-off-by: Fabian Frederick <fabf@skynet.be>
---
 drivers/acpi/sbs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/acpi/sbs.c b/drivers/acpi/sbs.c
index 32aecea..a7a3edd 100644
--- a/drivers/acpi/sbs.c
+++ b/drivers/acpi/sbs.c
@@ -441,7 +441,7 @@ static int acpi_ac_get_present(struct acpi_sbs *sbs)
 	 * The spec requires that bit 4 always be 1. If it's not set, assume
 	 * that the implementation doesn't support an SBS charger
 	 */
-	if (!(status >> 4) & 0x1)
+	if (!((status >> 4) & 0x1))
 		return -ENODEV;
 
 	sbs->charger_present = (status >> 15) & 0x1;
-- 
1.9.1

Re: [PATCH 1/1 linux-next] ACPI / SBS: fix sparse warning

[Sudip Mukherjee]

On Sun, Sep 28, 2014 at 08:44:47PM +0200, Fabian Frederick wrote:
> Adding parentheses around expression to avoid:
> drivers/acpi/sbs.c:444:28: warning: dubious: !x & y
> 
> Signed-off-by: Fabian Frederick <fabf@skynet.be>
> ---
>  drivers/acpi/sbs.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/acpi/sbs.c b/drivers/acpi/sbs.c
> index 32aecea..a7a3edd 100644
> --- a/drivers/acpi/sbs.c
> +++ b/drivers/acpi/sbs.c
> @@ -441,7 +441,7 @@ static int acpi_ac_get_present(struct acpi_sbs *sbs)
>  	 * The spec requires that bit 4 always be 1. If it's not set, assume
>  	 * that the implementation doesn't support an SBS charger
>  	 */
> -	if (!(status >> 4) & 0x1)
> +	if (!((status >> 4) & 0x1))

i think the logic changed over here.
it was !x & y , but now it has become !(x & y)
! is having higher priority than & so !x & y will mean ((!x) & y)

thanks
sudip
>  		return -ENODEV;
>  
>  	sbs->charger_present = (status >> 15) & 0x1;
> -- 
> 1.9.1
> 
> --
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Re: [PATCH 1/1 linux-next] ACPI / SBS: fix sparse warning

[Fabian Frederick]

> On 29 September 2014 at 07:40 Sudip Mukherjee <sudipm.mukherjee@gmail.com>
> wrote:
>
>
> On Sun, Sep 28, 2014 at 08:44:47PM +0200, Fabian Frederick wrote:
> > Adding parentheses around expression to avoid:
> > drivers/acpi/sbs.c:444:28: warning: dubious: !x & y
> >
> > Signed-off-by: Fabian Frederick <fabf@skynet.be>
> > ---
> >  drivers/acpi/sbs.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/acpi/sbs.c b/drivers/acpi/sbs.c
> > index 32aecea..a7a3edd 100644
> > --- a/drivers/acpi/sbs.c
> > +++ b/drivers/acpi/sbs.c
> > @@ -441,7 +441,7 @@ static int acpi_ac_get_present(struct acpi_sbs *sbs)
> >      * The spec requires that bit 4 always be 1. If it's not set, assume
> >      * that the implementation doesn't support an SBS charger
> >      */
> > -   if (!(status >> 4) & 0x1)
> > +   if (!((status >> 4) & 0x1))
>
> i think the logic changed over here.
> it was !x & y , but now it has become !(x & y)
> ! is having higher priority than & so !x & y will mean ((!x) & y)
>
> thanks
> sudip
Hello Sudip,

You're right, logic has changed but IMHO expression was wrong.

Let's take value 100, decimal.
Binary: 0110>0<100

Spec states that bit 4 must be 1 so value is wrong.

We don't go in
if (!(status>>4) & 0x1)

but

if (!((status>>4) & 0x1))
        return -ENODEV;

is triggered.

Regards,
Fabian
> >             return -ENODEV;
> > 
> >     sbs->charger_present = (status >> 15) & 0x1;
> > --
> > 1.9.1
> >
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > Please read the FAQ at  http://www.tux.org/lkml/

Re: [PATCH 1/1 linux-next] ACPI / SBS: fix sparse warning

[Rafael J. Wysocki]

On Sunday, September 28, 2014 08:44:47 PM Fabian Frederick wrote:
> Adding parentheses around expression to avoid:
> drivers/acpi/sbs.c:444:28: warning: dubious: !x & y
> 
> Signed-off-by: Fabian Frederick <fabf@skynet.be>

I was faster: https://patchwork.kernel.org/patch/4990671/


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.