On Thu, 05 Nov 2020, Jiri Slaby wrote:

On 05. 11. 20, 9:36, Lee Jones wrote:

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On Thu, 05 Nov 2020, Jiri Slaby wrote:

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On 05. 11. 20, 8:04, Christophe Leroy wrote:

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Le 04/11/2020 à 20:35, Lee Jones a écrit :

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Fixes the following W=1 kernel build warning(s):

   drivers/tty/serial/pmac_zilog.h:365:58: warning: variable
‘garbage’ set but not used [-Wunused-but-set-variable]

Explain how you are fixing this warning.

Setting  __always_unused is usually not the good solution for fixing
this warning, but here I guess this is likely the good solution. But it
should be explained why.

There are normally 3 ways to fix this warning;

  - Start using/checking the variable/result
  - Remove the variable
  - Mark it as __{always,maybe}_unused

The later just tells the compiler that not checking the resultant
value is intentional.  There are some functions (as Jiri mentions
below) which are marked as '__must_check' which *require* a dummy
(garbage) variable to be used.

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Or, why is the "garbage =" needed in the first place? read_zsdata is not
defined with __warn_unused_result__.

I used '__always_used' here for fear of breaking something.

However, if it's safe to remove it, then all the better.

Yes please -- this "garbage" is one of the examples of volatile misuses. If
readb didn't work on volatile pointer, marking the return variable as
volatile wouldn't save it.

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And even if it was, would (void)!read_zsdata(port) fix it?

That's hideous. :D

Sure, marking reads as must_check would be insane.

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*Much* better to just use '__always_used' in that use-case.

Then using a dummy variable to fool must_check must mean must_check is used
incorrectly, no :)? But there are always exceptions…

Agreed on all points.

Will fix.

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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