linux-kernel - Re: [PATCH 2/2] tick: SHUTDOWN event-dev if no events are required for KTIME

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Date:	Sat, 10 May 2014 13:01:15 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Viresh Kumar <viresh.kumar@...aro.org>
cc:	linaro-kernel@...ts.linaro.org, linux-kernel@...r.kernel.org,
	fweisbec@...il.com, arvind.chauhan@....com,
	preeti@...ux.vnet.ibm.com, khilman@...aro.org
Subject: Re: [PATCH 2/2] tick: SHUTDOWN event-dev if no events are required
 for KTIME_MAX

On Fri, 9 May 2014, Thomas Gleixner wrote:
> On Fri, 9 May 2014, Viresh Kumar wrote:
> So the right thing to do this is:
> 
> 1A) Change the prototype of the set_mode callback to return int and
>     fixup all users. Either add the missing default clause or remove
>     the existing BUG()/ pr_err()/whatever handling in the existing
>     default clause and return a UNIQUE error code.
> 
>     I know I should have done that from the very beginning, but in
>     hindsight one could have done everything better.
> 
>     coccinelle is your friend (if you need help ask me or Julia
>     Lawall). But it's going to be quite some manual work on top.

There is even a better way to do that:

1) Create a new callback set_state() which has an
   int return value.

2) Make the callsites do

   if (dev->set_state) {
      ret = dev->set_state();
      handle_return_value();
   } else
      dev->set_mode();

3) Convert implementations one by one to use the new callback

4) Remove the set_mode callback

5) Implement new features.

Thanks,

	tglx
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