Re: [PATCH] tty/serial: digicolor: Fix bad usage of IS_ERR_VALUE

[Arnd Bergmann]

On Tuesday 09 February 2016 18:37:46 Guenter Roeck wrote:
> On 02/09/2016 07:26 AM, Arnd Bergmann wrote:
> > On Tuesday 09 February 2016 07:08:59 Guenter Roeck wrote:
> >> IS_ERR_VALUE() assumes that its parameter is an unsigned long.
> >> It can not be used to check if an unsigned int reflects an error.
> >> Doing so can result in the following build warning.
> >>
> >> drivers/tty/serial/digicolor-usart.c: In function âdigicolor_uart_probeâ:
> >> include/linux/err.h:21:38: warning:
> >>          comparison is always false due to limited range of data type
> >> drivers/tty/serial/digicolor-usart.c:485:6: note:
> >>          in expansion of macro âIS_ERR_VALUEâ
> >>
> >> If that warning is seen, an error return from platform_get_irq() is missed.
> >>
> >>
> >
> > The patch looks correct to me, but what compiler version and which kernel
> > tree is it that triggered the warning?
> >
> > Andrzej Hajda just modified the definition of IS_ERR_VALUE(), and the
> > changes are still under discussion, but I don't see that warning with
> > any of the versions.
> >
> I see it with gcc 5.1 and 5.2 (and W=1). I did not see / notice Andrzej's patch.
> 
> I agree that fixing the problem in IS_ERR_VALUE() is preferrable.
> 
> 

Ah, W=1 explains it. We are still debating about the proper solution. Al Viro
pointed out that most users of IS_ERR_VALUE() shouldn't be using it at all,
so your patch is probably best here after all.

	Arnd